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  3. [PATCH v3 0/7] kbuild: various cleanups
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[PATCH v3 6/7] kbuild: use obj-y instead extra-y for objects placed at the head

Masahiro Yamada posted 7 patches 3 years, 6 months ago
[PATCH v3 6/7] kbuild: use obj-y instead extra-y for objects placed at the head
Posted by Masahiro Yamada 3 years, 6 months ago 
The objects placed at the head of vmlinux need special treatments:

 - arch/$(SRCARCH)/Makefile adds them to head-y in order to place
   them before other archives in the linker command line.

 - arch/$(SRCARCH)/kernel/Makefile adds them to extra-y instead of
   obj-y to avoid them going into built-in.a.

This commit gets rid of the latter.

Create vmlinux.a to collect all the objects that are unconditionally
linked to vmlinux. The objects listed in head-y are moved to the head
of vmlinux.a by using 'ar m'.

With this, arch/$(SRCARCH)/kernel/Makefile can consistently use obj-y
for builtin objects.

There is no *.o that is directly linked to vmlinux. Drop unneeded code
in scripts/clang-tools/gen_compile_commands.py.

$(AR) mPi needs 'T' to workaround the llvm-ar bug. The fix was suggested
by Nathan Chancellor [1].

[1]: https://lore.kernel.org/llvm/YyjjT5gQ2hGMH0ni@dev-arch.thelio-3990X/

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

Changes in v3:
  - Fix build error for m68k
  - Fix the bug for llvm-ar <= 14

 Documentation/kbuild/makefiles.rst          | 18 +---------------
 Makefile                                    | 23 ++++++++++++++++-----
 arch/alpha/kernel/Makefile                  |  4 ++--
 arch/arc/kernel/Makefile                    |  4 ++--
 arch/arm/kernel/Makefile                    |  4 ++--
 arch/arm64/kernel/Makefile                  |  4 ++--
 arch/csky/kernel/Makefile                   |  4 ++--
 arch/hexagon/kernel/Makefile                |  3 ++-
 arch/ia64/kernel/Makefile                   |  4 ++--
 arch/loongarch/kernel/Makefile              |  4 ++--
 arch/m68k/68000/Makefile                    |  2 +-
 arch/m68k/coldfire/Makefile                 |  2 +-
 arch/m68k/kernel/Makefile                   | 23 +++++++++++----------
 arch/microblaze/kernel/Makefile             |  4 ++--
 arch/mips/kernel/Makefile                   |  4 ++--
 arch/nios2/kernel/Makefile                  |  2 +-
 arch/openrisc/kernel/Makefile               |  4 ++--
 arch/parisc/kernel/Makefile                 |  4 ++--
 arch/powerpc/kernel/Makefile                | 20 +++++++++---------
 arch/riscv/kernel/Makefile                  |  2 +-
 arch/s390/kernel/Makefile                   |  4 ++--
 arch/sh/kernel/Makefile                     |  4 ++--
 arch/sparc/kernel/Makefile                  |  3 +--
 arch/x86/kernel/Makefile                    | 10 ++++-----
 arch/xtensa/kernel/Makefile                 |  4 ++--
 scripts/Makefile.modpost                    |  5 ++---
 scripts/Makefile.vmlinux_o                  |  6 +++---
 scripts/clang-tools/gen_compile_commands.py | 19 +----------------
 scripts/link-vmlinux.sh                     | 10 ++++-----
 29 files changed, 91 insertions(+), 113 deletions(-)

diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
index ee7e3ea1fbe1..5a6a8426cc97 100644
--- a/Documentation/kbuild/makefiles.rst
+++ b/Documentation/kbuild/makefiles.rst
@@ -340,19 +340,7 @@ more details, with real examples.
 
 	Examples are:
 
-	1) head objects
-
-	    Some objects must be placed at the head of vmlinux. They are
-	    directly linked to vmlinux without going through built-in.a
-	    A typical use-case is an object that contains the entry point.
-
-	    arch/$(SRCARCH)/Makefile should specify such objects as head-y.
-
-	    Discussion:
-	      Given that we can control the section order in the linker script,
-	      why do we need head-y?
-
-	2) vmlinux linker script
+	1) vmlinux linker script
 
 	    The linker script for vmlinux is located at
 	    arch/$(SRCARCH)/kernel/vmlinux.lds
@@ -360,10 +348,6 @@ more details, with real examples.
 	Example::
 
 		# arch/x86/kernel/Makefile
-		extra-y	:= head_$(BITS).o
-		extra-y	+= head$(BITS).o
-		extra-y	+= ebda.o
-		extra-y	+= platform-quirks.o
 		extra-y	+= vmlinux.lds
 
 	$(extra-y) should only contain targets needed for vmlinux.
diff --git a/Makefile b/Makefile
index cf9d7b1d8c14..a8c19f92ac9e 100644
--- a/Makefile
+++ b/Makefile
@@ -645,6 +645,8 @@ else
 __all: modules
 endif
 
+targets :=
+
 # Decide whether to build built-in, modular, or both.
 # Normally, just do built-in.
 
@@ -1107,7 +1109,7 @@ export ARCH_LIB		:= $(filter %/, $(libs-y))
 export ARCH_DRIVERS	:= $(drivers-y) $(drivers-m)
 # Externally visible symbols (used by link-vmlinux.sh)
 
-KBUILD_VMLINUX_OBJS := $(head-y) ./built-in.a
+KBUILD_VMLINUX_OBJS := ./built-in.a
 ifdef CONFIG_MODULES
 KBUILD_VMLINUX_OBJS += $(patsubst %/, %/lib.a, $(filter %/, $(libs-y)))
 KBUILD_VMLINUX_LIBS := $(filter-out %/, $(libs-y))
@@ -1115,7 +1117,7 @@ else
 KBUILD_VMLINUX_LIBS := $(patsubst %/,%/lib.a, $(libs-y))
 endif
 
-export KBUILD_VMLINUX_OBJS KBUILD_VMLINUX_LIBS
+export KBUILD_VMLINUX_LIBS
 export KBUILD_LDS          := arch/$(SRCARCH)/kernel/vmlinux.lds
 
 vmlinux-deps := $(KBUILD_LDS) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS)
@@ -1142,7 +1144,18 @@ quiet_cmd_autoksyms_h = GEN     $@
 $(autoksyms_h):
 	$(call cmd,autoksyms_h)
 
-vmlinux.o: autoksyms_recursive $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
+# '$(AR) mPi' needs 'T' to workaround the bug of llvm-ar <= 14
+quiet_cmd_ar_vmlinux.a = AR      $@
+      cmd_ar_vmlinux.a = \
+	rm -f $@; \
+	$(AR) cDPrST $@ $(KBUILD_VMLINUX_OBJS); \
+	$(AR) mPiT $$($(AR) t $@ | head -n1) $@ $(head-y)
+
+targets += vmlinux.a
+vmlinux.a: $(KBUILD_VMLINUX_OBJS) FORCE
+	$(call if_changed,ar_vmlinux.a)
+
+vmlinux.o: autoksyms_recursive vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux_o
 
 ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
@@ -1155,7 +1168,7 @@ cmd_link-vmlinux =                                                 \
 vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) modpost FORCE
 	+$(call if_changed_dep,link-vmlinux)
 
-targets := vmlinux
+targets += vmlinux
 
 # The actual objects are generated when descending,
 # make sure no implicit rule kicks in
@@ -1880,7 +1893,7 @@ quiet_cmd_gen_compile_commands = GEN     $@
       cmd_gen_compile_commands = $(PYTHON3) $< -a $(AR) -o $@ $(filter-out $<, $(real-prereqs))
 
 $(extmod_prefix)compile_commands.json: scripts/clang-tools/gen_compile_commands.py \
-	$(if $(KBUILD_EXTMOD),,$(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS)) \
+	$(if $(KBUILD_EXTMOD),, vmlinux.a $(KBUILD_VMLINUX_LIBS)) \
 	$(if $(CONFIG_MODULES), $(MODORDER)) FORCE
 	$(call if_changed,gen_compile_commands)
 
diff --git a/arch/alpha/kernel/Makefile b/arch/alpha/kernel/Makefile
index 5a74581bf0ee..5a5b0a8b7c6a 100644
--- a/arch/alpha/kernel/Makefile
+++ b/arch/alpha/kernel/Makefile
@@ -3,11 +3,11 @@
 # Makefile for the linux kernel.
 #
 
-extra-y		:= head.o vmlinux.lds
+extra-y		:= vmlinux.lds
 asflags-y	:= $(KBUILD_CFLAGS)
 ccflags-y	:= -Wno-sign-compare
 
-obj-y    := entry.o traps.o process.o osf_sys.o irq.o \
+obj-y    := head.o entry.o traps.o process.o osf_sys.o irq.o \
 	    irq_alpha.o signal.o setup.o ptrace.o time.o \
 	    systbls.o err_common.o io.o bugs.o
 
diff --git a/arch/arc/kernel/Makefile b/arch/arc/kernel/Makefile
index 8c4fc4b54c14..0723d888ac44 100644
--- a/arch/arc/kernel/Makefile
+++ b/arch/arc/kernel/Makefile
@@ -3,7 +3,7 @@
 # Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 #
 
-obj-y	:= arcksyms.o setup.o irq.o reset.o ptrace.o process.o devtree.o
+obj-y	:= head.o arcksyms.o setup.o irq.o reset.o ptrace.o process.o devtree.o
 obj-y	+= signal.o traps.o sys.o troubleshoot.o stacktrace.o disasm.o
 obj-$(CONFIG_ISA_ARCOMPACT)		+= entry-compact.o intc-compact.o
 obj-$(CONFIG_ISA_ARCV2)			+= entry-arcv2.o intc-arcv2.o
@@ -31,4 +31,4 @@ else
 obj-y += ctx_sw_asm.o
 endif
 
-extra-y := vmlinux.lds head.o
+extra-y := vmlinux.lds
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 553866751e1a..8feaa3217ec5 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -89,7 +89,7 @@ obj-$(CONFIG_VDSO)		+= vdso.o
 obj-$(CONFIG_EFI)		+= efi.o
 obj-$(CONFIG_PARAVIRT)	+= paravirt.o
 
-head-y			:= head$(MMUEXT).o
+obj-y			+= head$(MMUEXT).o
 obj-$(CONFIG_DEBUG_LL)	+= debug.o
 obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
 obj-$(CONFIG_ARM_PATCH_PHYS_VIRT)	+= phys2virt.o
@@ -109,4 +109,4 @@ obj-$(CONFIG_HAVE_ARM_SMCCC)	+= smccc-call.o
 
 obj-$(CONFIG_GENERIC_CPU_VULNERABILITIES) += spectre.o
 
-extra-y := $(head-y) vmlinux.lds
+extra-y := vmlinux.lds
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 1add7b01efa7..b619ff207a57 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -85,8 +85,8 @@ $(obj)/vdso-wrap.o: $(obj)/vdso/vdso.so
 $(obj)/vdso32-wrap.o: $(obj)/vdso32/vdso.so
 
 obj-y					+= probes/
-head-y					:= head.o
-extra-y					+= $(head-y) vmlinux.lds
+obj-y					+= head.o
+extra-y					+= vmlinux.lds
 
 ifeq ($(CONFIG_DEBUG_EFI),y)
 AFLAGS_head.o += -DVMLINUX_PATH="\"$(realpath $(objtree)/vmlinux)\""
diff --git a/arch/csky/kernel/Makefile b/arch/csky/kernel/Makefile
index 6f14c924b20d..8a868316b912 100644
--- a/arch/csky/kernel/Makefile
+++ b/arch/csky/kernel/Makefile
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
-extra-y := head.o vmlinux.lds
+extra-y := vmlinux.lds
 
-obj-y += entry.o atomic.o signal.o traps.o irq.o time.o vdso.o vdso/
+obj-y += head.o entry.o atomic.o signal.o traps.o irq.o time.o vdso.o vdso/
 obj-y += power.o syscall.o syscall_table.o setup.o io.o
 obj-y += process.o cpu-probe.o ptrace.o stacktrace.o
 obj-y += probes/
diff --git a/arch/hexagon/kernel/Makefile b/arch/hexagon/kernel/Makefile
index fae3dce32fde..e73cb321630e 100644
--- a/arch/hexagon/kernel/Makefile
+++ b/arch/hexagon/kernel/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
-extra-y := head.o vmlinux.lds
+extra-y := vmlinux.lds
 
+obj-y += head.o
 obj-$(CONFIG_SMP) += smp.o
 
 obj-y += setup.o irq_cpu.o traps.o syscalltab.o signal.o time.o
diff --git a/arch/ia64/kernel/Makefile b/arch/ia64/kernel/Makefile
index 08d4a2ba0652..4a1fcb121dda 100644
--- a/arch/ia64/kernel/Makefile
+++ b/arch/ia64/kernel/Makefile
@@ -7,9 +7,9 @@ ifdef CONFIG_DYNAMIC_FTRACE
 CFLAGS_REMOVE_ftrace.o = -pg
 endif
 
-extra-y	:= head.o vmlinux.lds
+extra-y	:= vmlinux.lds
 
-obj-y := entry.o efi.o efi_stub.o gate-data.o fsys.o irq.o irq_ia64.o	\
+obj-y := head.o entry.o efi.o efi_stub.o gate-data.o fsys.o irq.o irq_ia64.o	\
 	 irq_lsapic.o ivt.o pal.o patch.o process.o ptrace.o sal.o		\
 	 salinfo.o setup.o signal.o sys_ia64.o time.o traps.o unaligned.o \
 	 unwind.o mca.o mca_asm.o topology.o dma-mapping.o iosapic.o acpi.o \
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index e5be17009fe8..6c33b5c45573 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -3,9 +3,9 @@
 # Makefile for the Linux/LoongArch kernel.
 #
 
-extra-y		:= head.o vmlinux.lds
+extra-y		:= vmlinux.lds
 
-obj-y		+= cpu-probe.o cacheinfo.o env.o setup.o entry.o genex.o \
+obj-y		+= head.o cpu-probe.o cacheinfo.o env.o setup.o entry.o genex.o \
 		   traps.o irq.o idle.o process.o dma.o mem.o io.o reset.o switch.o \
 		   elf.o syscall.o signal.o time.o topology.o inst.o ptrace.o vdso.o
 
diff --git a/arch/m68k/68000/Makefile b/arch/m68k/68000/Makefile
index 674541fdf5b8..279560add577 100644
--- a/arch/m68k/68000/Makefile
+++ b/arch/m68k/68000/Makefile
@@ -17,4 +17,4 @@ obj-$(CONFIG_DRAGEN2)	+= dragen2.o
 obj-$(CONFIG_UCSIMM)	+= ucsimm.o
 obj-$(CONFIG_UCDIMM)	+= ucsimm.o
 
-extra-y 		:= head.o
+obj-y			+= head.o
diff --git a/arch/m68k/coldfire/Makefile b/arch/m68k/coldfire/Makefile
index 9419a6c1f036..c56bc0dc7f2e 100644
--- a/arch/m68k/coldfire/Makefile
+++ b/arch/m68k/coldfire/Makefile
@@ -45,4 +45,4 @@ obj-$(CONFIG_STMARK2)	+= stmark2.o
 obj-$(CONFIG_PCI)	+= pci.o
 
 obj-y			+= gpio.o
-extra-y := head.o
+obj-y			+= head.o
diff --git a/arch/m68k/kernel/Makefile b/arch/m68k/kernel/Makefile
index c0833da6a2ca..af015447dfb4 100644
--- a/arch/m68k/kernel/Makefile
+++ b/arch/m68k/kernel/Makefile
@@ -3,19 +3,20 @@
 # Makefile for the linux kernel.
 #
 
-extra-$(CONFIG_AMIGA)	:= head.o
-extra-$(CONFIG_ATARI)	:= head.o
-extra-$(CONFIG_MAC)	:= head.o
-extra-$(CONFIG_APOLLO)	:= head.o
-extra-$(CONFIG_VME)	:= head.o
-extra-$(CONFIG_HP300)	:= head.o
-extra-$(CONFIG_Q40)	:= head.o
-extra-$(CONFIG_SUN3X)	:= head.o
-extra-$(CONFIG_VIRT)	:= head.o
-extra-$(CONFIG_SUN3)	:= sun3-head.o
 extra-y			+= vmlinux.lds
 
-obj-y	:= entry.o irq.o module.o process.o ptrace.o
+obj-$(CONFIG_AMIGA)	:= head.o
+obj-$(CONFIG_ATARI)	:= head.o
+obj-$(CONFIG_MAC)	:= head.o
+obj-$(CONFIG_APOLLO)	:= head.o
+obj-$(CONFIG_VME)	:= head.o
+obj-$(CONFIG_HP300)	:= head.o
+obj-$(CONFIG_Q40)	:= head.o
+obj-$(CONFIG_SUN3X)	:= head.o
+obj-$(CONFIG_VIRT)	:= head.o
+obj-$(CONFIG_SUN3)	:= sun3-head.o
+
+obj-y	+= entry.o irq.o module.o process.o ptrace.o
 obj-y	+= setup.o signal.o sys_m68k.o syscalltable.o time.o traps.o
 
 obj-$(CONFIG_MMU_MOTOROLA) += ints.o vectors.o
diff --git a/arch/microblaze/kernel/Makefile b/arch/microblaze/kernel/Makefile
index 15a20eb814ce..4393bee64eaf 100644
--- a/arch/microblaze/kernel/Makefile
+++ b/arch/microblaze/kernel/Makefile
@@ -12,9 +12,9 @@ CFLAGS_REMOVE_ftrace.o = -pg
 CFLAGS_REMOVE_process.o = -pg
 endif
 
-extra-y := head.o vmlinux.lds
+extra-y := vmlinux.lds
 
-obj-y += dma.o exceptions.o \
+obj-y += head.o dma.o exceptions.o \
 	hw_exception_handler.o irq.o \
 	process.o prom.o ptrace.o \
 	reset.o setup.o signal.o sys_microblaze.o timer.o traps.o unwind.o
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 7c96282bff2e..5d1addac5e28 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -3,9 +3,9 @@
 # Makefile for the Linux/MIPS kernel.
 #
 
-extra-y		:= head.o vmlinux.lds
+extra-y		:= vmlinux.lds
 
-obj-y		+= branch.o cmpxchg.o elf.o entry.o genex.o idle.o irq.o \
+obj-y		+= head.o branch.o cmpxchg.o elf.o entry.o genex.o idle.o irq.o \
 		   process.o prom.o ptrace.o reset.o setup.o signal.o \
 		   syscall.o time.o topology.o traps.o unaligned.o watch.o \
 		   vdso.o cacheinfo.o
diff --git a/arch/nios2/kernel/Makefile b/arch/nios2/kernel/Makefile
index 0b645e1e3158..78a913181fa1 100644
--- a/arch/nios2/kernel/Makefile
+++ b/arch/nios2/kernel/Makefile
@@ -3,9 +3,9 @@
 # Makefile for the nios2 linux kernel.
 #
 
-extra-y	+= head.o
 extra-y	+= vmlinux.lds
 
+obj-y	+= head.o
 obj-y	+= cpuinfo.o
 obj-y	+= entry.o
 obj-y	+= insnemu.o
diff --git a/arch/openrisc/kernel/Makefile b/arch/openrisc/kernel/Makefile
index 2d172e79f58d..79129161f3e0 100644
--- a/arch/openrisc/kernel/Makefile
+++ b/arch/openrisc/kernel/Makefile
@@ -3,9 +3,9 @@
 # Makefile for the linux kernel.
 #
 
-extra-y	:= head.o vmlinux.lds
+extra-y	:= vmlinux.lds
 
-obj-y	:= setup.o or32_ksyms.o process.o dma.o \
+obj-y	:= head.o setup.o or32_ksyms.o process.o dma.o \
 	   traps.o time.o irq.o entry.o ptrace.o signal.o \
 	   sys_call_table.o unwinder.o
 
diff --git a/arch/parisc/kernel/Makefile b/arch/parisc/kernel/Makefile
index d0bfac89a842..3d138c9cf9ce 100644
--- a/arch/parisc/kernel/Makefile
+++ b/arch/parisc/kernel/Makefile
@@ -3,9 +3,9 @@
 # Makefile for arch/parisc/kernel
 #
 
-extra-y			:= head.o vmlinux.lds
+extra-y		:= vmlinux.lds
 
-obj-y	     	:= cache.o pacache.o setup.o pdt.o traps.o time.o irq.o \
+obj-y		:= head.o cache.o pacache.o setup.o pdt.o traps.o time.o irq.o \
 		   pa7300lc.o syscall.o entry.o sys_parisc.o firmware.o \
 		   ptrace.o hardware.o inventory.o drivers.o alternative.o \
 		   signal.o hpmc.o real2.o parisc_ksyms.o unaligned.o \
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 06d2d1f78f71..ad3decb9f20b 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -118,12 +118,12 @@ obj-$(CONFIG_PPC_FSL_BOOK3E)	+= cpu_setup_fsl_booke.o
 obj-$(CONFIG_PPC_DOORBELL)	+= dbell.o
 obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
 
-extra-$(CONFIG_PPC64)		:= head_64.o
-extra-$(CONFIG_PPC_BOOK3S_32)	:= head_book3s_32.o
-extra-$(CONFIG_40x)		:= head_40x.o
-extra-$(CONFIG_44x)		:= head_44x.o
-extra-$(CONFIG_FSL_BOOKE)	:= head_fsl_booke.o
-extra-$(CONFIG_PPC_8xx)		:= head_8xx.o
+obj-$(CONFIG_PPC64)		+= head_64.o
+obj-$(CONFIG_PPC_BOOK3S_32)	+= head_book3s_32.o
+obj-$(CONFIG_40x)		+= head_40x.o
+obj-$(CONFIG_44x)		+= head_44x.o
+obj-$(CONFIG_FSL_BOOKE)		+= head_fsl_booke.o
+obj-$(CONFIG_PPC_8xx)		+= head_8xx.o
 extra-y				+= vmlinux.lds
 
 obj-$(CONFIG_RELOCATABLE)	+= reloc_$(BITS).o
@@ -198,10 +198,10 @@ KCOV_INSTRUMENT_paca.o := n
 CFLAGS_setup_64.o		+= -fno-stack-protector
 CFLAGS_paca.o			+= -fno-stack-protector
 
-extra-$(CONFIG_PPC_FPU)		+= fpu.o
-extra-$(CONFIG_ALTIVEC)		+= vector.o
-extra-$(CONFIG_PPC64)		+= entry_64.o
-extra-$(CONFIG_PPC_OF_BOOT_TRAMPOLINE)	+= prom_init.o
+obj-$(CONFIG_PPC_FPU)		+= fpu.o
+obj-$(CONFIG_ALTIVEC)		+= vector.o
+obj-$(CONFIG_PPC64)		+= entry_64.o
+obj-$(CONFIG_PPC_OF_BOOT_TRAMPOLINE)	+= prom_init.o
 
 extra-$(CONFIG_PPC_OF_BOOT_TRAMPOLINE)	+= prom_init_check
 
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 33bb60a354cd..db6e4b1294ba 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -28,9 +28,9 @@ KASAN_SANITIZE_cpufeature.o := n
 endif
 endif
 
-extra-y += head.o
 extra-y += vmlinux.lds
 
+obj-y	+= head.o
 obj-y	+= soc.o
 obj-$(CONFIG_RISCV_ALTERNATIVE) += alternative.o
 obj-y	+= cpu.o
diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
index 3cbfa9fddd9a..7ce00816b8df 100644
--- a/arch/s390/kernel/Makefile
+++ b/arch/s390/kernel/Makefile
@@ -33,7 +33,7 @@ CFLAGS_stacktrace.o	+= -fno-optimize-sibling-calls
 CFLAGS_dumpstack.o	+= -fno-optimize-sibling-calls
 CFLAGS_unwind_bc.o	+= -fno-optimize-sibling-calls
 
-obj-y	:= traps.o time.o process.o earlypgm.o early.o setup.o idle.o vtime.o
+obj-y	:= head64.o traps.o time.o process.o earlypgm.o early.o setup.o idle.o vtime.o
 obj-y	+= processor.o syscall.o ptrace.o signal.o cpcmd.o ebcdic.o nmi.o
 obj-y	+= debug.o irq.o ipl.o dis.o diag.o vdso.o cpufeature.o
 obj-y	+= sysinfo.o lgr.o os_info.o machine_kexec.o
@@ -42,7 +42,7 @@ obj-y	+= entry.o reipl.o relocate_kernel.o kdebugfs.o alternative.o
 obj-y	+= nospec-branch.o ipl_vmparm.o machine_kexec_reloc.o unwind_bc.o
 obj-y	+= smp.o text_amode31.o stacktrace.o
 
-extra-y				+= head64.o vmlinux.lds
+extra-y				+= vmlinux.lds
 
 obj-$(CONFIG_SYSFS)		+= nospec-sysfs.o
 CFLAGS_REMOVE_nospec-branch.o	+= $(CC_FLAGS_EXPOLINE)
diff --git a/arch/sh/kernel/Makefile b/arch/sh/kernel/Makefile
index aa0fbc9202b1..69cd9ac4b2ab 100644
--- a/arch/sh/kernel/Makefile
+++ b/arch/sh/kernel/Makefile
@@ -3,7 +3,7 @@
 # Makefile for the Linux/SuperH kernel.
 #
 
-extra-y	:= head_32.o vmlinux.lds
+extra-y	:= vmlinux.lds
 
 ifdef CONFIG_FUNCTION_TRACER
 # Do not profile debug and lowlevel utilities
@@ -12,7 +12,7 @@ endif
 
 CFLAGS_REMOVE_return_address.o = -pg
 
-obj-y	:= debugtraps.o dumpstack.o 		\
+obj-y	:= head_32.o debugtraps.o dumpstack.o				\
 	   idle.o io.o irq.o irq_32.o kdebugfs.o			\
 	   machvec.o nmi_debug.o process.o				\
 	   process_32.o ptrace.o ptrace_32.o				\
diff --git a/arch/sparc/kernel/Makefile b/arch/sparc/kernel/Makefile
index d3a0e072ebe8..b328e4a0bd57 100644
--- a/arch/sparc/kernel/Makefile
+++ b/arch/sparc/kernel/Makefile
@@ -7,8 +7,6 @@
 asflags-y := -ansi
 ccflags-y := -Werror
 
-extra-y     := head_$(BITS).o
-
 # Undefine sparc when processing vmlinux.lds - it is used
 # And teach CPP we are doing $(BITS) builds (for this case)
 CPPFLAGS_vmlinux.lds := -Usparc -m$(BITS)
@@ -22,6 +20,7 @@ CFLAGS_REMOVE_perf_event.o := -pg
 CFLAGS_REMOVE_pcr.o := -pg
 endif
 
+obj-y                   := head_$(BITS).o
 obj-$(CONFIG_SPARC64)   += urtt_fill.o
 obj-$(CONFIG_SPARC32)   += entry.o wof.o wuf.o
 obj-$(CONFIG_SPARC32)   += etrap_32.o
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index a20a5ebfacd7..956e50ca06e0 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -3,10 +3,6 @@
 # Makefile for the linux kernel.
 #
 
-extra-y	:= head_$(BITS).o
-extra-y	+= head$(BITS).o
-extra-y	+= ebda.o
-extra-y	+= platform-quirks.o
 extra-y	+= vmlinux.lds
 
 CPPFLAGS_vmlinux.lds += -U$(UTS_MACHINE)
@@ -42,7 +38,11 @@ KCOV_INSTRUMENT		:= n
 
 CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace
 
-obj-y			:= process_$(BITS).o signal.o
+obj-y			+= head_$(BITS).o
+obj-y			+= head$(BITS).o
+obj-y			+= ebda.o
+obj-y			+= platform-quirks.o
+obj-y			+= process_$(BITS).o signal.o
 obj-$(CONFIG_COMPAT)	+= signal_compat.o
 obj-y			+= traps.o idt.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
 obj-y			+= time.o ioport.o dumpstack.o nmi.o
diff --git a/arch/xtensa/kernel/Makefile b/arch/xtensa/kernel/Makefile
index 897c1c741058..f28b8e3d717e 100644
--- a/arch/xtensa/kernel/Makefile
+++ b/arch/xtensa/kernel/Makefile
@@ -3,9 +3,9 @@
 # Makefile for the Linux/Xtensa kernel.
 #
 
-extra-y := head.o vmlinux.lds
+extra-y := vmlinux.lds
 
-obj-y := align.o coprocessor.o entry.o irq.o platform.o process.o \
+obj-y := head.o align.o coprocessor.o entry.o irq.o platform.o process.o \
 	 ptrace.o setup.o signal.o stacktrace.o syscall.o time.o traps.o \
 	 vectors.o
 
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 2daf760eeb25..ceb1d78140e7 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -70,13 +70,12 @@ quiet_cmd_vmlinux_objs = GEN     $@
 	for f in $(real-prereqs); do	\
 		case $${f} in		\
 		*libgcc.a) ;;		\
-		*.a) $(AR) t $${f} ;;	\
-		*) echo $${f} ;;	\
+		*) $(AR) t $${f} ;;	\
 		esac			\
 	done > $@
 
 targets += .vmlinux.objs
-.vmlinux.objs: $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
+.vmlinux.objs: vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
 	$(call if_changed,vmlinux_objs)
 
 vmlinux.o-if-present := $(wildcard vmlinux.o)
diff --git a/scripts/Makefile.vmlinux_o b/scripts/Makefile.vmlinux_o
index 84019814f33f..81a4e0484457 100644
--- a/scripts/Makefile.vmlinux_o
+++ b/scripts/Makefile.vmlinux_o
@@ -18,7 +18,7 @@ quiet_cmd_gen_initcalls_lds = GEN     $@
 	$(PERL) $(real-prereqs) > $@
 
 .tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \
-		$(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
+		vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
 	$(call if_changed,gen_initcalls_lds)
 
 targets := .tmp_initcalls.lds
@@ -55,7 +55,7 @@ quiet_cmd_ld_vmlinux.o = LD      $@
       cmd_ld_vmlinux.o = \
 	$(LD) ${KBUILD_LDFLAGS} -r -o $@ \
 	$(addprefix -T , $(initcalls-lds)) \
-	--whole-archive $(KBUILD_VMLINUX_OBJS) --no-whole-archive \
+	--whole-archive vmlinux.a --no-whole-archive \
 	--start-group $(KBUILD_VMLINUX_LIBS) --end-group \
 	$(cmd_objtool)
 
@@ -64,7 +64,7 @@ define rule_ld_vmlinux.o
 	$(call cmd,gen_objtooldep)
 endef
 
-vmlinux.o: $(initcalls-lds) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
+vmlinux.o: $(initcalls-lds) vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
 	$(call if_changed_rule,ld_vmlinux.o)
 
 targets += vmlinux.o
diff --git a/scripts/clang-tools/gen_compile_commands.py b/scripts/clang-tools/gen_compile_commands.py
index 47da25b3ba7d..d800b2c0af97 100755
--- a/scripts/clang-tools/gen_compile_commands.py
+++ b/scripts/clang-tools/gen_compile_commands.py
@@ -109,20 +109,6 @@ def to_cmdfile(path):
     return os.path.join(dir, '.' + base + '.cmd')
 
 
-def cmdfiles_for_o(obj):
-    """Generate the iterator of .cmd files associated with the object
-
-    Yield the .cmd file used to build the given object
-
-    Args:
-        obj: The object path
-
-    Yields:
-        The path to .cmd file
-    """
-    yield to_cmdfile(obj)
-
-
 def cmdfiles_for_a(archive, ar):
     """Generate the iterator of .cmd files associated with the archive.
 
@@ -211,13 +197,10 @@ def main():
     for path in paths:
         # If 'path' is a directory, handle all .cmd files under it.
         # Otherwise, handle .cmd files associated with the file.
-        # Most of built-in objects are linked via archives (built-in.a or lib.a)
-        # but some objects are linked to vmlinux directly.
+        # built-in objects are linked via vmlinux.a
         # Modules are listed in modules.order.
         if os.path.isdir(path):
             cmdfiles = cmdfiles_in_dir(path)
-        elif path.endswith('.o'):
-            cmdfiles = cmdfiles_for_o(path)
         elif path.endswith('.a'):
             cmdfiles = cmdfiles_for_a(path, ar)
         elif path.endswith('modules.order'):
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 6a197d8a88ac..23ac13fd9d89 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -3,17 +3,15 @@
 #
 # link vmlinux
 #
-# vmlinux is linked from the objects selected by $(KBUILD_VMLINUX_OBJS) and
-# $(KBUILD_VMLINUX_LIBS). Most are built-in.a files from top-level directories
-# in the kernel tree, others are specified in arch/$(ARCH)/Makefile.
+# vmlinux is linked from the objects in vmlinux.a and $(KBUILD_VMLINUX_LIBS).
+# vmlinux.a contains objects that are linked unconditionally.
 # $(KBUILD_VMLINUX_LIBS) are archives which are linked conditionally
 # (not within --whole-archive), and do not require symbol indexes added.
 #
 # vmlinux
 #   ^
 #   |
-#   +--< $(KBUILD_VMLINUX_OBJS)
-#   |    +--< init/built-in.a drivers/built-in.a mm/built-in.a + more
+#   +--< vmlinux.a
 #   |
 #   +--< $(KBUILD_VMLINUX_LIBS)
 #   |    +--< lib/lib.a + more
@@ -67,7 +65,7 @@ vmlinux_link()
 		objs=vmlinux.o
 		libs=
 	else
-		objs="${KBUILD_VMLINUX_OBJS}"
+		objs=vmlinux.a
 		libs="${KBUILD_VMLINUX_LIBS}"
 	fi
 
-- 
2.34.1
Re: [PATCH v3 6/7] kbuild: use obj-y instead extra-y for objects placed at the head
Posted by Jiri Slaby 3 years, 5 months ago 
Hi,

following an IRC discussion with many parties...

On 24. 09. 22, 20:19, Masahiro Yamada wrote:
> The objects placed at the head of vmlinux need special treatments:
> 
>   - arch/$(SRCARCH)/Makefile adds them to head-y in order to place
>     them before other archives in the linker command line.
> 
>   - arch/$(SRCARCH)/kernel/Makefile adds them to extra-y instead of
>     obj-y to avoid them going into built-in.a.
> 
> This commit gets rid of the latter.
> 
> Create vmlinux.a to collect all the objects that are unconditionally
> linked to vmlinux. The objects listed in head-y are moved to the head
> of vmlinux.a by using 'ar m'.
> 
> With this, arch/$(SRCARCH)/kernel/Makefile can consistently use obj-y
> for builtin objects.
> 
> There is no *.o that is directly linked to vmlinux. Drop unneeded code
> in scripts/clang-tools/gen_compile_commands.py.
> 
> $(AR) mPi needs 'T' to workaround the llvm-ar bug. The fix was suggested
> by Nathan Chancellor [1].
> 
> [1]: https://lore.kernel.org/llvm/YyjjT5gQ2hGMH0ni@dev-arch.thelio-3990X/
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
...
> --- a/scripts/Makefile.vmlinux_o
> +++ b/scripts/Makefile.vmlinux_o
> @@ -18,7 +18,7 @@ quiet_cmd_gen_initcalls_lds = GEN     $@
>   	$(PERL) $(real-prereqs) > $@
>   
>   .tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \
> -		$(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
> +		vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE

There is a slight problem with this. The kernel built with gcc-LTO does 
not boot. But as I understand it, it's not limited to gcc-LTO only.

On x86, startup_64() is supposed to be at offset >zero< of the image 
(see .Lrelocated()). It was ensured by putting head64.o to the beginning 
of vmlinux (by KBUILD_VMLINUX_OBJS on the LD command-line above). The 
patch above instead packs head64.o into vmlinux.a and then moves it 
using "ar -m" to the beginning (it's in 7/7 of the series IIRC).

The problem is that .o files listed on the LD command line explicitly 
are taken as spelled. But unpacking .a inside LD gives no guarantees on 
the order of packed objects. To quote: "that it happens to work 
sometimes is pure luck." (Correct me guys, if I misunderstood you.)

For x86, the most ideal fix seems to be to fix it in the linker script. 
By putting startup_64() to a different section and handle it in the ld 
script specially -- see the attachment. It should always have been put 
this way, the command line order is only a workaround. But this might 
need more fixes on other archs too -- I haven't take a look.

Ideas, comments? I'll send the attachment as a PATCH later (if there are 
no better suggestions).

thanks,
-- 
js
suse labs
Re: [PATCH v3 6/7] kbuild: use obj-y instead extra-y for objects placed at the head
Posted by Michael Matz 3 years, 5 months ago 
Hello,

On Mon, 24 Oct 2022, Jiri Slaby wrote:

> > Create vmlinux.a to collect all the objects that are unconditionally
> > linked to vmlinux. The objects listed in head-y are moved to the head
> > of vmlinux.a by using 'ar m'.
... 
> > --- a/scripts/Makefile.vmlinux_o
> > +++ b/scripts/Makefile.vmlinux_o
> > @@ -18,7 +18,7 @@ quiet_cmd_gen_initcalls_lds = GEN     $@
> >   	$(PERL) $(real-prereqs) > $@
> >     .tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \
> > -		$(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
> > +		vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
> 
> There is a slight problem with this. The kernel built with gcc-LTO does not
> boot. But as I understand it, it's not limited to gcc-LTO only.
> 
> On x86, startup_64() is supposed to be at offset >zero< of the image (see
> .Lrelocated()). It was ensured by putting head64.o to the beginning of vmlinux
> (by KBUILD_VMLINUX_OBJS on the LD command-line above). The patch above instead
> packs head64.o into vmlinux.a and then moves it using "ar -m" to the beginning
> (it's in 7/7 of the series IIRC).
> 
> The problem is that .o files listed on the LD command line explicitly are
> taken as spelled. But unpacking .a inside LD gives no guarantees on the order
> of packed objects. To quote: "that it happens to work sometimes is pure luck."
> (Correct me guys, if I misunderstood you.)

To be precise: I know of no linker (outside LTO-like modes) that processes 
archives in a different order than first-to-last-member (under 
whole-archive), but that's not guaranteed anywhere.  So relying on 
member-order within archives is always brittle.

It will completely break down with LTO modes: the granularity for that is 
functions, and they are placed in some unknown (from the outside, but 
usually related to call-graph locality) order into several partitions, 
with non-LTO-able parts (like asm code) being placed randomly between 
them.  The order of these blobs can not be defined in relation to the 
input order of object files: with cross-file dependencies such order might 
not even exist.  Those whole sequence of blobs then takes the place of the 
input archive (which, as there was only one, has no particular order from 
the linker command lines perspective).

There are only two ways of guaranteeing an ordering: put non-LTO-.o files 
at certain places of the link command, or, better, use a linker script to 
specify an order.

> For x86, the most ideal fix seems to be to fix it in the linker script. By
> putting startup_64() to a different section and handle it in the ld script
> specially -- see the attachment. It should always have been put this way, the
> command line order is only a workaround. But this might need more fixes on
> other archs too -- I haven't take a look.
> 
> Ideas, comments? I'll send the attachment as a PATCH later (if there are 
> no better suggestions).

This will work.  An alternative way would be to explicitely name the input 
file in the section commands, without renaming the section:

@@ -126,6 +126,7 @@ SECTIONS
                _text = .;
                _stext = .;
                /* bootstrapping code */
+               KEEP(vmlinux.a:head64.o(.head.text))
                HEAD_TEXT
                TEXT_TEXT

But I guess not all arch's name their must-be-first file head64.o (or even 
have such requirement), so that's probably still arch-dependend and hence 
not inherently better than your way.

(syntax for the section selector in linkerscripts is:

  {archive-glob:}filename-glob (sectionname-glob)


Ciao,
Michael.
Re: [PATCH v3 6/7] kbuild: use obj-y instead extra-y for objects placed at the head
Posted by Masahiro Yamada 3 years, 5 months ago 
On Tue, Oct 25, 2022 at 2:26 PM Michael Matz <matz@suse.de> wrote:
>
> Hello,
>
> On Mon, 24 Oct 2022, Jiri Slaby wrote:
>
> > > Create vmlinux.a to collect all the objects that are unconditionally
> > > linked to vmlinux. The objects listed in head-y are moved to the head
> > > of vmlinux.a by using 'ar m'.
> ...
> > > --- a/scripts/Makefile.vmlinux_o
> > > +++ b/scripts/Makefile.vmlinux_o
> > > @@ -18,7 +18,7 @@ quiet_cmd_gen_initcalls_lds = GEN     $@
> > >     $(PERL) $(real-prereqs) > $@
> > >     .tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \
> > > -           $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
> > > +           vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
> >
> > There is a slight problem with this. The kernel built with gcc-LTO does not
> > boot. But as I understand it, it's not limited to gcc-LTO only.
> >
> > On x86, startup_64() is supposed to be at offset >zero< of the image (see
> > .Lrelocated()). It was ensured by putting head64.o to the beginning of vmlinux
> > (by KBUILD_VMLINUX_OBJS on the LD command-line above). The patch above instead
> > packs head64.o into vmlinux.a and then moves it using "ar -m" to the beginning
> > (it's in 7/7 of the series IIRC).
> >
> > The problem is that .o files listed on the LD command line explicitly are
> > taken as spelled. But unpacking .a inside LD gives no guarantees on the order
> > of packed objects. To quote: "that it happens to work sometimes is pure luck."
> > (Correct me guys, if I misunderstood you.)
>
> To be precise: I know of no linker (outside LTO-like modes) that processes
> archives in a different order than first-to-last-member (under
> whole-archive), but that's not guaranteed anywhere.  So relying on
> member-order within archives is always brittle.


The objects in an archive are linked first-to-last-member for a long time.
This is the assumption which we have relied on for a long time.


We assume the initcall order is preserved.
The call order within each of core_initcall, arch_initcall,
device_initcall, etc.
is the order of objects in built-in.a, in other words,
the order they appear in Makefiles.


If this assumption were broken, the initcall order would be randomised.
(Somebody would have screamed earlier, if so.)



Clang LTO came up with its own workaround.
See commit a8cccdd954732a558d481407ab7c3106b89c34ae


So, this is happening on (not-upstreamed-yet) GCC LTO only?





> It will completely break down with LTO modes: the granularity for that is
> functions, and they are placed in some unknown (from the outside, but
> usually related to call-graph locality) order into several partitions,
> with non-LTO-able parts (like asm code) being placed randomly between
> them.  The order of these blobs can not be defined in relation to the
> input order of object files: with cross-file dependencies such order might
> not even exist.  Those whole sequence of blobs then takes the place of the
> input archive (which, as there was only one, has no particular order from
> the linker command lines perspective).
>
> There are only two ways of guaranteeing an ordering: put non-LTO-.o files
> at certain places of the link command, or, better, use a linker script to
> specify an order.


The objects directly given in the command line are linked in the same order,
even under LTO mode. Is this what you mean?

Any documentation about that?





> > For x86, the most ideal fix seems to be to fix it in the linker script. By
> > putting startup_64() to a different section and handle it in the ld script
> > specially -- see the attachment. It should always have been put this way, the
> > command line order is only a workaround. But this might need more fixes on
> > other archs too -- I haven't take a look.
> >
> > Ideas, comments? I'll send the attachment as a PATCH later (if there are
> > no better suggestions).
>
> This will work.  An alternative way would be to explicitely name the input
> file in the section commands, without renaming the section:
>
> @@ -126,6 +126,7 @@ SECTIONS
>                 _text = .;
>                 _stext = .;
>                 /* bootstrapping code */
> +               KEEP(vmlinux.a:head64.o(.head.text))
>                 HEAD_TEXT
>                 TEXT_TEXT
>
> But I guess not all arch's name their must-be-first file head64.o (or even
> have such requirement), so that's probably still arch-dependend and hence
> not inherently better than your way.
>
> (syntax for the section selector in linkerscripts is:
>
>   {archive-glob:}filename-glob (sectionname-glob)
>
>
> Ciao,
> Michael.



--
Best Regards

Masahiro Yamada
Re: [PATCH v3 6/7] kbuild: use obj-y instead extra-y for objects placed at the head
Posted by Michael Matz 3 years, 5 months ago 
Hello,

On Thu, 27 Oct 2022, Masahiro Yamada wrote:

> > To be precise: I know of no linker (outside LTO-like modes) that processes
> > archives in a different order than first-to-last-member (under
> > whole-archive), but that's not guaranteed anywhere.  So relying on
> > member-order within archives is always brittle.
> 
> The objects in an archive are linked first-to-last-member for a long time.
> This is the assumption which we have relied on for a long time.

Sure, that doesn't mean it's guaranteed, for this I'm just devils 
advocate.  As I said, it's the mode of operation of all currently existing 
linkers I know, so for the forseeable future you can continue to rely on 
it.  But as soon as LTO enters the picture that all breaks down, as you 
see here.

Consider how LTO works, the granularity of shuffling stuff around is the 
functions of all inputs, not the object files.  So, even if you say
  obj1.o obj2.o
on the link command line, and supposed there are two functions in each of 
obj1 and obj2, then it may just so happen that LTO partitions the program 
such that it ends up with partitions
  part1 : obj1:foo obj2:bar
  part2 : obj1:bar obj2:foo
now, suddenly there is no order between part1 and part2 anymore that 
would faithfully represent the original order between obj1 and obj2 
functions.  Of course the partitioning algorithm could be changed, but 
that would limit the effectiveness of LTO.

> We assume the initcall order is preserved.
> The call order within each of core_initcall, arch_initcall,
> device_initcall, etc.
> is the order of objects in built-in.a, in other words,
> the order they appear in Makefiles.

If you rely on relative order of these, then you will probably see 
interesting effects in LTO mode eventually.

> So, this is happening on (not-upstreamed-yet) GCC LTO only?

I don't know.  As any kind of whole-program transformations is in 
principle cross-file on per-function basis (that's the whole purpose) I 
would imagine that you can see these effects in all compilers, if you try 
hard enough.

> > There are only two ways of guaranteeing an ordering: put non-LTO-.o files
> > at certain places of the link command, or, better, use a linker script to
> > specify an order.
> 
> The objects directly given in the command line are linked in the same order,
> even under LTO mode. Is this what you mean?

If they don't contain LTO code then yes, they are linked 
in exactly the given order.  If they do, they become part of the LTO blob 
whose ordering isn't precisely influenced by cmdline order.

> Any documentation about that?

I think so, but I can't point my finger to anything.  Several parts of the 
toolchain rely on that (so the kernel is not alone), but those are either 
carefully avoiding LTO or using other ordering means like linker script to 
achieve what they need.


Ciao,
Michael.
Re: [PATCH v3 6/7] kbuild: use obj-y instead extra-y for objects placed at the head
Posted by Jiri Slaby 3 years, 5 months ago 
On 25. 10. 22, 14:26, Michael Matz wrote:
>> Ideas, comments? I'll send the attachment as a PATCH later (if there are
>> no better suggestions).
> 
> This will work.  An alternative way would be to explicitly name the input
> file in the section commands, without renaming the section:
> 
> @@ -126,6 +126,7 @@ SECTIONS
>                  _text = .;
>                  _stext = .;
>                  /* bootstrapping code */
> +               KEEP(vmlinux.a:head64.o(.head.text))
>                  HEAD_TEXT
>                  TEXT_TEXT
> 
> But I guess not all arch's name their must-be-first file head64.o (or even
> have such requirement), so that's probably still arch-dependend and hence
> not inherently better than your way.

The downside of this is that it doesn't make sure the function 
(startup_64()) is the first one. When someone sticks something before 
it, it breaks again. But leaving the decision up to the x86 maintainers ;).

Re. other archs, I have absolutely no idea (haven't looked into that at 
all).

thanks,
-- 
js
Re: [PATCH v3 6/7] kbuild: use obj-y instead extra-y for objects placed at the head
Posted by Ard Biesheuvel 3 years, 5 months ago 
On Wed, 26 Oct 2022 at 10:35, Jiri Slaby <jirislaby@kernel.org> wrote:
>
> On 25. 10. 22, 14:26, Michael Matz wrote:
> >> Ideas, comments? I'll send the attachment as a PATCH later (if there are
> >> no better suggestions).
> >
> > This will work.  An alternative way would be to explicitly name the input
> > file in the section commands, without renaming the section:
> >
> > @@ -126,6 +126,7 @@ SECTIONS
> >                  _text = .;
> >                  _stext = .;
> >                  /* bootstrapping code */
> > +               KEEP(vmlinux.a:head64.o(.head.text))
> >                  HEAD_TEXT
> >                  TEXT_TEXT
> >
> > But I guess not all arch's name their must-be-first file head64.o (or even
> > have such requirement), so that's probably still arch-dependend and hence
> > not inherently better than your way.
>
> The downside of this is that it doesn't make sure the function
> (startup_64()) is the first one. When someone sticks something before
> it, it breaks again. But leaving the decision up to the x86 maintainers ;).
>
> Re. other archs, I have absolutely no idea (haven't looked into that at
> all).
>

I seriously doubt that those __head routines need to be in .head.text.
At the time, there seems to have been some regression related to
5-level paging, but whether and how that change actually fixed
anything at all is undocumented.

So the fix here is to move those __head routines into __init, so that
only startup_64 remains in .head.text, and the existing linker script
will put it where it belongs.





commit 26179670a68b7b365fbfe38afb043dcd2e1a4678
Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Date:   Fri Jun 16 14:30:24 2017 +0300

    x86/boot/64: Put __startup_64() into .head.text

    Put __startup_64() and fixup_pointer() into .head.text section to make
    sure it's always near startup_64() and always callable.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: kernel test robot <fengguang.wu@intel.com>
    Cc: wfg@linux.intel.com
    Link: http://lkml.kernel.org/r/20170616113024.ajmif63cmcszry5a@black.fi.intel.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
Re: [PATCH v3 6/7] kbuild: use obj-y instead extra-y for objects placed at the head
Posted by Nicolas Schier 3 years, 6 months ago 
On Sun, 25 Sep 2022 03:19:14 +0900 Masahiro Yamada wrote:
> The objects placed at the head of vmlinux need special treatments:
> 
>  - arch/$(SRCARCH)/Makefile adds them to head-y in order to place
>    them before other archives in the linker command line.
> 
>  - arch/$(SRCARCH)/kernel/Makefile adds them to extra-y instead of
>    obj-y to avoid them going into built-in.a.
> 
> This commit gets rid of the latter.
> 
> Create vmlinux.a to collect all the objects that are unconditionally
> linked to vmlinux. The objects listed in head-y are moved to the head
> of vmlinux.a by using 'ar m'.
> 
> With this, arch/$(SRCARCH)/kernel/Makefile can consistently use obj-y
> for builtin objects.
> 
> There is no *.o that is directly linked to vmlinux. Drop unneeded code
> in scripts/clang-tools/gen_compile_commands.py.
> 
> $(AR) mPi needs 'T' to workaround the llvm-ar bug. The fix was suggested
> by Nathan Chancellor [1].
> 
> [1]: https://lore.kernel.org/llvm/YyjjT5gQ2hGMH0ni@dev-arch.thelio-3990X/
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---

Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>


> Changes in v3:
>   - Fix build error for m68k
>   - Fix the bug for llvm-ar <= 14
> 
>  Documentation/kbuild/makefiles.rst          | 18 +---------------
>  Makefile                                    | 23 ++++++++++++++++-----
>  arch/alpha/kernel/Makefile                  |  4 ++--
>  arch/arc/kernel/Makefile                    |  4 ++--
>  arch/arm/kernel/Makefile                    |  4 ++--
>  arch/arm64/kernel/Makefile                  |  4 ++--
>  arch/csky/kernel/Makefile                   |  4 ++--
>  arch/hexagon/kernel/Makefile                |  3 ++-
>  arch/ia64/kernel/Makefile                   |  4 ++--
>  arch/loongarch/kernel/Makefile              |  4 ++--
>  arch/m68k/68000/Makefile                    |  2 +-
>  arch/m68k/coldfire/Makefile                 |  2 +-
>  arch/m68k/kernel/Makefile                   | 23 +++++++++++----------
>  arch/microblaze/kernel/Makefile             |  4 ++--
>  arch/mips/kernel/Makefile                   |  4 ++--
>  arch/nios2/kernel/Makefile                  |  2 +-
>  arch/openrisc/kernel/Makefile               |  4 ++--
>  arch/parisc/kernel/Makefile                 |  4 ++--
>  arch/powerpc/kernel/Makefile                | 20 +++++++++---------
>  arch/riscv/kernel/Makefile                  |  2 +-
>  arch/s390/kernel/Makefile                   |  4 ++--
>  arch/sh/kernel/Makefile                     |  4 ++--
>  arch/sparc/kernel/Makefile                  |  3 +--
>  arch/x86/kernel/Makefile                    | 10 ++++-----
>  arch/xtensa/kernel/Makefile                 |  4 ++--
>  scripts/Makefile.modpost                    |  5 ++---
>  scripts/Makefile.vmlinux_o                  |  6 +++---
>  scripts/clang-tools/gen_compile_commands.py | 19 +----------------
>  scripts/link-vmlinux.sh                     | 10 ++++-----
>  29 files changed, 91 insertions(+), 113 deletions(-)
> 
> diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
> index ee7e3ea1fbe1..5a6a8426cc97 100644
> --- a/Documentation/kbuild/makefiles.rst
> +++ b/Documentation/kbuild/makefiles.rst
> @@ -340,19 +340,7 @@ more details, with real examples.
>  
>  	Examples are:
>  
> -	1) head objects
> -
> -	    Some objects must be placed at the head of vmlinux. They are
> -	    directly linked to vmlinux without going through built-in.a
> -	    A typical use-case is an object that contains the entry point.
> -
> -	    arch/$(SRCARCH)/Makefile should specify such objects as head-y.
> -
> -	    Discussion:
> -	      Given that we can control the section order in the linker script,
> -	      why do we need head-y?
> -
> -	2) vmlinux linker script
> +	1) vmlinux linker script
>  
>  	    The linker script for vmlinux is located at
>  	    arch/$(SRCARCH)/kernel/vmlinux.lds
> @@ -360,10 +348,6 @@ more details, with real examples.
>  	Example::
>  
>  		# arch/x86/kernel/Makefile
> -		extra-y	:= head_$(BITS).o
> -		extra-y	+= head$(BITS).o
> -		extra-y	+= ebda.o
> -		extra-y	+= platform-quirks.o
>  		extra-y	+= vmlinux.lds
>  
>  	$(extra-y) should only contain targets needed for vmlinux.
> diff --git a/Makefile b/Makefile
> index cf9d7b1d8c14..a8c19f92ac9e 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -645,6 +645,8 @@ else
>  __all: modules
>  endif
>  
> +targets :=
> +
>  # Decide whether to build built-in, modular, or both.
>  # Normally, just do built-in.
>  
> @@ -1107,7 +1109,7 @@ export ARCH_LIB		:= $(filter %/, $(libs-y))
>  export ARCH_DRIVERS	:= $(drivers-y) $(drivers-m)
>  # Externally visible symbols (used by link-vmlinux.sh)
>  
> -KBUILD_VMLINUX_OBJS := $(head-y) ./built-in.a
> +KBUILD_VMLINUX_OBJS := ./built-in.a
>  ifdef CONFIG_MODULES
>  KBUILD_VMLINUX_OBJS += $(patsubst %/, %/lib.a, $(filter %/, $(libs-y)))
>  KBUILD_VMLINUX_LIBS := $(filter-out %/, $(libs-y))
> @@ -1115,7 +1117,7 @@ else
>  KBUILD_VMLINUX_LIBS := $(patsubst %/,%/lib.a, $(libs-y))
>  endif
>  
> -export KBUILD_VMLINUX_OBJS KBUILD_VMLINUX_LIBS
> +export KBUILD_VMLINUX_LIBS
>  export KBUILD_LDS          := arch/$(SRCARCH)/kernel/vmlinux.lds
>  
>  vmlinux-deps := $(KBUILD_LDS) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS)
> @@ -1142,7 +1144,18 @@ quiet_cmd_autoksyms_h = GEN     $@
>  $(autoksyms_h):
>  	$(call cmd,autoksyms_h)
>  
> -vmlinux.o: autoksyms_recursive $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
> +# '$(AR) mPi' needs 'T' to workaround the bug of llvm-ar <= 14
> +quiet_cmd_ar_vmlinux.a = AR      $@
> +      cmd_ar_vmlinux.a = \
> +	rm -f $@; \
> +	$(AR) cDPrST $@ $(KBUILD_VMLINUX_OBJS); \
> +	$(AR) mPiT $$($(AR) t $@ | head -n1) $@ $(head-y)
> +
> +targets += vmlinux.a
> +vmlinux.a: $(KBUILD_VMLINUX_OBJS) FORCE
> +	$(call if_changed,ar_vmlinux.a)
> +
> +vmlinux.o: autoksyms_recursive vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
>  	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux_o
>  
>  ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
> @@ -1155,7 +1168,7 @@ cmd_link-vmlinux =                                                 \
>  vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) modpost FORCE
>  	+$(call if_changed_dep,link-vmlinux)
>  
> -targets := vmlinux
> +targets += vmlinux
>  
>  # The actual objects are generated when descending,
>  # make sure no implicit rule kicks in
> @@ -1880,7 +1893,7 @@ quiet_cmd_gen_compile_commands = GEN     $@
>        cmd_gen_compile_commands = $(PYTHON3) $< -a $(AR) -o $@ $(filter-out $<, $(real-prereqs))
>  
>  $(extmod_prefix)compile_commands.json: scripts/clang-tools/gen_compile_commands.py \
> -	$(if $(KBUILD_EXTMOD),,$(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS)) \
> +	$(if $(KBUILD_EXTMOD),, vmlinux.a $(KBUILD_VMLINUX_LIBS)) \
>  	$(if $(CONFIG_MODULES), $(MODORDER)) FORCE
>  	$(call if_changed,gen_compile_commands)
>  
> diff --git a/arch/alpha/kernel/Makefile b/arch/alpha/kernel/Makefile
> index 5a74581bf0ee..5a5b0a8b7c6a 100644
> --- a/arch/alpha/kernel/Makefile
> +++ b/arch/alpha/kernel/Makefile
> @@ -3,11 +3,11 @@
>  # Makefile for the linux kernel.
>  #
>  
> -extra-y		:= head.o vmlinux.lds
> +extra-y		:= vmlinux.lds
>  asflags-y	:= $(KBUILD_CFLAGS)
>  ccflags-y	:= -Wno-sign-compare
>  
> -obj-y    := entry.o traps.o process.o osf_sys.o irq.o \
> +obj-y    := head.o entry.o traps.o process.o osf_sys.o irq.o \
>  	    irq_alpha.o signal.o setup.o ptrace.o time.o \
>  	    systbls.o err_common.o io.o bugs.o
>  
> diff --git a/arch/arc/kernel/Makefile b/arch/arc/kernel/Makefile
> index 8c4fc4b54c14..0723d888ac44 100644
> --- a/arch/arc/kernel/Makefile
> +++ b/arch/arc/kernel/Makefile
> @@ -3,7 +3,7 @@
>  # Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
>  #
>  
> -obj-y	:= arcksyms.o setup.o irq.o reset.o ptrace.o process.o devtree.o
> +obj-y	:= head.o arcksyms.o setup.o irq.o reset.o ptrace.o process.o devtree.o
>  obj-y	+= signal.o traps.o sys.o troubleshoot.o stacktrace.o disasm.o
>  obj-$(CONFIG_ISA_ARCOMPACT)		+= entry-compact.o intc-compact.o
>  obj-$(CONFIG_ISA_ARCV2)			+= entry-arcv2.o intc-arcv2.o
> @@ -31,4 +31,4 @@ else
>  obj-y += ctx_sw_asm.o
>  endif
>  
> -extra-y := vmlinux.lds head.o
> +extra-y := vmlinux.lds
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index 553866751e1a..8feaa3217ec5 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -89,7 +89,7 @@ obj-$(CONFIG_VDSO)		+= vdso.o
>  obj-$(CONFIG_EFI)		+= efi.o
>  obj-$(CONFIG_PARAVIRT)	+= paravirt.o
>  
> -head-y			:= head$(MMUEXT).o
> +obj-y			+= head$(MMUEXT).o
>  obj-$(CONFIG_DEBUG_LL)	+= debug.o
>  obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
>  obj-$(CONFIG_ARM_PATCH_PHYS_VIRT)	+= phys2virt.o
> @@ -109,4 +109,4 @@ obj-$(CONFIG_HAVE_ARM_SMCCC)	+= smccc-call.o
>  
>  obj-$(CONFIG_GENERIC_CPU_VULNERABILITIES) += spectre.o
>  
> -extra-y := $(head-y) vmlinux.lds
> +extra-y := vmlinux.lds
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 1add7b01efa7..b619ff207a57 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -85,8 +85,8 @@ $(obj)/vdso-wrap.o: $(obj)/vdso/vdso.so
>  $(obj)/vdso32-wrap.o: $(obj)/vdso32/vdso.so
>  
>  obj-y					+= probes/
> -head-y					:= head.o
> -extra-y					+= $(head-y) vmlinux.lds
> +obj-y					+= head.o
> +extra-y					+= vmlinux.lds
>  
>  ifeq ($(CONFIG_DEBUG_EFI),y)
>  AFLAGS_head.o += -DVMLINUX_PATH="\"$(realpath $(objtree)/vmlinux)\""
> diff --git a/arch/csky/kernel/Makefile b/arch/csky/kernel/Makefile
> index 6f14c924b20d..8a868316b912 100644
> --- a/arch/csky/kernel/Makefile
> +++ b/arch/csky/kernel/Makefile
> @@ -1,7 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> -extra-y := head.o vmlinux.lds
> +extra-y := vmlinux.lds
>  
> -obj-y += entry.o atomic.o signal.o traps.o irq.o time.o vdso.o vdso/
> +obj-y += head.o entry.o atomic.o signal.o traps.o irq.o time.o vdso.o vdso/
>  obj-y += power.o syscall.o syscall_table.o setup.o io.o
>  obj-y += process.o cpu-probe.o ptrace.o stacktrace.o
>  obj-y += probes/
> diff --git a/arch/hexagon/kernel/Makefile b/arch/hexagon/kernel/Makefile
> index fae3dce32fde..e73cb321630e 100644
> --- a/arch/hexagon/kernel/Makefile
> +++ b/arch/hexagon/kernel/Makefile
> @@ -1,6 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0
> -extra-y := head.o vmlinux.lds
> +extra-y := vmlinux.lds
>  
> +obj-y += head.o
>  obj-$(CONFIG_SMP) += smp.o
>  
>  obj-y += setup.o irq_cpu.o traps.o syscalltab.o signal.o time.o
> diff --git a/arch/ia64/kernel/Makefile b/arch/ia64/kernel/Makefile
> index 08d4a2ba0652..4a1fcb121dda 100644
> --- a/arch/ia64/kernel/Makefile
> +++ b/arch/ia64/kernel/Makefile
> @@ -7,9 +7,9 @@ ifdef CONFIG_DYNAMIC_FTRACE
>  CFLAGS_REMOVE_ftrace.o = -pg
>  endif
>  
> -extra-y	:= head.o vmlinux.lds
> +extra-y	:= vmlinux.lds
>  
> -obj-y := entry.o efi.o efi_stub.o gate-data.o fsys.o irq.o irq_ia64.o	\
> +obj-y := head.o entry.o efi.o efi_stub.o gate-data.o fsys.o irq.o irq_ia64.o	\
>  	 irq_lsapic.o ivt.o pal.o patch.o process.o ptrace.o sal.o		\
>  	 salinfo.o setup.o signal.o sys_ia64.o time.o traps.o unaligned.o \
>  	 unwind.o mca.o mca_asm.o topology.o dma-mapping.o iosapic.o acpi.o \
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index e5be17009fe8..6c33b5c45573 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -3,9 +3,9 @@
>  # Makefile for the Linux/LoongArch kernel.
>  #
>  
> -extra-y		:= head.o vmlinux.lds
> +extra-y		:= vmlinux.lds
>  
> -obj-y		+= cpu-probe.o cacheinfo.o env.o setup.o entry.o genex.o \
> +obj-y		+= head.o cpu-probe.o cacheinfo.o env.o setup.o entry.o genex.o \
>  		   traps.o irq.o idle.o process.o dma.o mem.o io.o reset.o switch.o \
>  		   elf.o syscall.o signal.o time.o topology.o inst.o ptrace.o vdso.o
>  
> diff --git a/arch/m68k/68000/Makefile b/arch/m68k/68000/Makefile
> index 674541fdf5b8..279560add577 100644
> --- a/arch/m68k/68000/Makefile
> +++ b/arch/m68k/68000/Makefile
> @@ -17,4 +17,4 @@ obj-$(CONFIG_DRAGEN2)	+= dragen2.o
>  obj-$(CONFIG_UCSIMM)	+= ucsimm.o
>  obj-$(CONFIG_UCDIMM)	+= ucsimm.o
>  
> -extra-y 		:= head.o
> +obj-y			+= head.o
> diff --git a/arch/m68k/coldfire/Makefile b/arch/m68k/coldfire/Makefile
> index 9419a6c1f036..c56bc0dc7f2e 100644
> --- a/arch/m68k/coldfire/Makefile
> +++ b/arch/m68k/coldfire/Makefile
> @@ -45,4 +45,4 @@ obj-$(CONFIG_STMARK2)	+= stmark2.o
>  obj-$(CONFIG_PCI)	+= pci.o
>  
>  obj-y			+= gpio.o
> -extra-y := head.o
> +obj-y			+= head.o
> diff --git a/arch/m68k/kernel/Makefile b/arch/m68k/kernel/Makefile
> index c0833da6a2ca..af015447dfb4 100644
> --- a/arch/m68k/kernel/Makefile
> +++ b/arch/m68k/kernel/Makefile
> @@ -3,19 +3,20 @@
>  # Makefile for the linux kernel.
>  #
>  
> -extra-$(CONFIG_AMIGA)	:= head.o
> -extra-$(CONFIG_ATARI)	:= head.o
> -extra-$(CONFIG_MAC)	:= head.o
> -extra-$(CONFIG_APOLLO)	:= head.o
> -extra-$(CONFIG_VME)	:= head.o
> -extra-$(CONFIG_HP300)	:= head.o
> -extra-$(CONFIG_Q40)	:= head.o
> -extra-$(CONFIG_SUN3X)	:= head.o
> -extra-$(CONFIG_VIRT)	:= head.o
> -extra-$(CONFIG_SUN3)	:= sun3-head.o
>  extra-y			+= vmlinux.lds
>  
> -obj-y	:= entry.o irq.o module.o process.o ptrace.o
> +obj-$(CONFIG_AMIGA)	:= head.o
> +obj-$(CONFIG_ATARI)	:= head.o
> +obj-$(CONFIG_MAC)	:= head.o
> +obj-$(CONFIG_APOLLO)	:= head.o
> +obj-$(CONFIG_VME)	:= head.o
> +obj-$(CONFIG_HP300)	:= head.o
> +obj-$(CONFIG_Q40)	:= head.o
> +obj-$(CONFIG_SUN3X)	:= head.o
> +obj-$(CONFIG_VIRT)	:= head.o
> +obj-$(CONFIG_SUN3)	:= sun3-head.o
> +
> +obj-y	+= entry.o irq.o module.o process.o ptrace.o
>  obj-y	+= setup.o signal.o sys_m68k.o syscalltable.o time.o traps.o
>  
>  obj-$(CONFIG_MMU_MOTOROLA) += ints.o vectors.o
> diff --git a/arch/microblaze/kernel/Makefile b/arch/microblaze/kernel/Makefile
> index 15a20eb814ce..4393bee64eaf 100644
> --- a/arch/microblaze/kernel/Makefile
> +++ b/arch/microblaze/kernel/Makefile
> @@ -12,9 +12,9 @@ CFLAGS_REMOVE_ftrace.o = -pg
>  CFLAGS_REMOVE_process.o = -pg
>  endif
>  
> -extra-y := head.o vmlinux.lds
> +extra-y := vmlinux.lds
>  
> -obj-y += dma.o exceptions.o \
> +obj-y += head.o dma.o exceptions.o \
>  	hw_exception_handler.o irq.o \
>  	process.o prom.o ptrace.o \
>  	reset.o setup.o signal.o sys_microblaze.o timer.o traps.o unwind.o
> diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
> index 7c96282bff2e..5d1addac5e28 100644
> --- a/arch/mips/kernel/Makefile
> +++ b/arch/mips/kernel/Makefile
> @@ -3,9 +3,9 @@
>  # Makefile for the Linux/MIPS kernel.
>  #
>  
> -extra-y		:= head.o vmlinux.lds
> +extra-y		:= vmlinux.lds
>  
> -obj-y		+= branch.o cmpxchg.o elf.o entry.o genex.o idle.o irq.o \
> +obj-y		+= head.o branch.o cmpxchg.o elf.o entry.o genex.o idle.o irq.o \
>  		   process.o prom.o ptrace.o reset.o setup.o signal.o \
>  		   syscall.o time.o topology.o traps.o unaligned.o watch.o \
>  		   vdso.o cacheinfo.o
> diff --git a/arch/nios2/kernel/Makefile b/arch/nios2/kernel/Makefile
> index 0b645e1e3158..78a913181fa1 100644
> --- a/arch/nios2/kernel/Makefile
> +++ b/arch/nios2/kernel/Makefile
> @@ -3,9 +3,9 @@
>  # Makefile for the nios2 linux kernel.
>  #
>  
> -extra-y	+= head.o
>  extra-y	+= vmlinux.lds
>  
> +obj-y	+= head.o
>  obj-y	+= cpuinfo.o
>  obj-y	+= entry.o
>  obj-y	+= insnemu.o
> diff --git a/arch/openrisc/kernel/Makefile b/arch/openrisc/kernel/Makefile
> index 2d172e79f58d..79129161f3e0 100644
> --- a/arch/openrisc/kernel/Makefile
> +++ b/arch/openrisc/kernel/Makefile
> @@ -3,9 +3,9 @@
>  # Makefile for the linux kernel.
>  #
>  
> -extra-y	:= head.o vmlinux.lds
> +extra-y	:= vmlinux.lds
>  
> -obj-y	:= setup.o or32_ksyms.o process.o dma.o \
> +obj-y	:= head.o setup.o or32_ksyms.o process.o dma.o \
>  	   traps.o time.o irq.o entry.o ptrace.o signal.o \
>  	   sys_call_table.o unwinder.o
>  
> diff --git a/arch/parisc/kernel/Makefile b/arch/parisc/kernel/Makefile
> index d0bfac89a842..3d138c9cf9ce 100644
> --- a/arch/parisc/kernel/Makefile
> +++ b/arch/parisc/kernel/Makefile
> @@ -3,9 +3,9 @@
>  # Makefile for arch/parisc/kernel
>  #
>  
> -extra-y			:= head.o vmlinux.lds
> +extra-y		:= vmlinux.lds
>  
> -obj-y	     	:= cache.o pacache.o setup.o pdt.o traps.o time.o irq.o \
> +obj-y		:= head.o cache.o pacache.o setup.o pdt.o traps.o time.o irq.o \
>  		   pa7300lc.o syscall.o entry.o sys_parisc.o firmware.o \
>  		   ptrace.o hardware.o inventory.o drivers.o alternative.o \
>  		   signal.o hpmc.o real2.o parisc_ksyms.o unaligned.o \
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 06d2d1f78f71..ad3decb9f20b 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -118,12 +118,12 @@ obj-$(CONFIG_PPC_FSL_BOOK3E)	+= cpu_setup_fsl_booke.o
>  obj-$(CONFIG_PPC_DOORBELL)	+= dbell.o
>  obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
>  
> -extra-$(CONFIG_PPC64)		:= head_64.o
> -extra-$(CONFIG_PPC_BOOK3S_32)	:= head_book3s_32.o
> -extra-$(CONFIG_40x)		:= head_40x.o
> -extra-$(CONFIG_44x)		:= head_44x.o
> -extra-$(CONFIG_FSL_BOOKE)	:= head_fsl_booke.o
> -extra-$(CONFIG_PPC_8xx)		:= head_8xx.o
> +obj-$(CONFIG_PPC64)		+= head_64.o
> +obj-$(CONFIG_PPC_BOOK3S_32)	+= head_book3s_32.o
> +obj-$(CONFIG_40x)		+= head_40x.o
> +obj-$(CONFIG_44x)		+= head_44x.o
> +obj-$(CONFIG_FSL_BOOKE)		+= head_fsl_booke.o
> +obj-$(CONFIG_PPC_8xx)		+= head_8xx.o
>  extra-y				+= vmlinux.lds
>  
>  obj-$(CONFIG_RELOCATABLE)	+= reloc_$(BITS).o
> @@ -198,10 +198,10 @@ KCOV_INSTRUMENT_paca.o := n
>  CFLAGS_setup_64.o		+= -fno-stack-protector
>  CFLAGS_paca.o			+= -fno-stack-protector
>  
> -extra-$(CONFIG_PPC_FPU)		+= fpu.o
> -extra-$(CONFIG_ALTIVEC)		+= vector.o
> -extra-$(CONFIG_PPC64)		+= entry_64.o
> -extra-$(CONFIG_PPC_OF_BOOT_TRAMPOLINE)	+= prom_init.o
> +obj-$(CONFIG_PPC_FPU)		+= fpu.o
> +obj-$(CONFIG_ALTIVEC)		+= vector.o
> +obj-$(CONFIG_PPC64)		+= entry_64.o
> +obj-$(CONFIG_PPC_OF_BOOT_TRAMPOLINE)	+= prom_init.o
>  
>  extra-$(CONFIG_PPC_OF_BOOT_TRAMPOLINE)	+= prom_init_check
>  
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index 33bb60a354cd..db6e4b1294ba 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -28,9 +28,9 @@ KASAN_SANITIZE_cpufeature.o := n
>  endif
>  endif
>  
> -extra-y += head.o
>  extra-y += vmlinux.lds
>  
> +obj-y	+= head.o
>  obj-y	+= soc.o
>  obj-$(CONFIG_RISCV_ALTERNATIVE) += alternative.o
>  obj-y	+= cpu.o
> diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
> index 3cbfa9fddd9a..7ce00816b8df 100644
> --- a/arch/s390/kernel/Makefile
> +++ b/arch/s390/kernel/Makefile
> @@ -33,7 +33,7 @@ CFLAGS_stacktrace.o	+= -fno-optimize-sibling-calls
>  CFLAGS_dumpstack.o	+= -fno-optimize-sibling-calls
>  CFLAGS_unwind_bc.o	+= -fno-optimize-sibling-calls
>  
> -obj-y	:= traps.o time.o process.o earlypgm.o early.o setup.o idle.o vtime.o
> +obj-y	:= head64.o traps.o time.o process.o earlypgm.o early.o setup.o idle.o vtime.o
>  obj-y	+= processor.o syscall.o ptrace.o signal.o cpcmd.o ebcdic.o nmi.o
>  obj-y	+= debug.o irq.o ipl.o dis.o diag.o vdso.o cpufeature.o
>  obj-y	+= sysinfo.o lgr.o os_info.o machine_kexec.o
> @@ -42,7 +42,7 @@ obj-y	+= entry.o reipl.o relocate_kernel.o kdebugfs.o alternative.o
>  obj-y	+= nospec-branch.o ipl_vmparm.o machine_kexec_reloc.o unwind_bc.o
>  obj-y	+= smp.o text_amode31.o stacktrace.o
>  
> -extra-y				+= head64.o vmlinux.lds
> +extra-y				+= vmlinux.lds
>  
>  obj-$(CONFIG_SYSFS)		+= nospec-sysfs.o
>  CFLAGS_REMOVE_nospec-branch.o	+= $(CC_FLAGS_EXPOLINE)
> diff --git a/arch/sh/kernel/Makefile b/arch/sh/kernel/Makefile
> index aa0fbc9202b1..69cd9ac4b2ab 100644
> --- a/arch/sh/kernel/Makefile
> +++ b/arch/sh/kernel/Makefile
> @@ -3,7 +3,7 @@
>  # Makefile for the Linux/SuperH kernel.
>  #
>  
> -extra-y	:= head_32.o vmlinux.lds
> +extra-y	:= vmlinux.lds
>  
>  ifdef CONFIG_FUNCTION_TRACER
>  # Do not profile debug and lowlevel utilities
> @@ -12,7 +12,7 @@ endif
>  
>  CFLAGS_REMOVE_return_address.o = -pg
>  
> -obj-y	:= debugtraps.o dumpstack.o 		\
> +obj-y	:= head_32.o debugtraps.o dumpstack.o				\
>  	   idle.o io.o irq.o irq_32.o kdebugfs.o			\
>  	   machvec.o nmi_debug.o process.o				\
>  	   process_32.o ptrace.o ptrace_32.o				\
> diff --git a/arch/sparc/kernel/Makefile b/arch/sparc/kernel/Makefile
> index d3a0e072ebe8..b328e4a0bd57 100644
> --- a/arch/sparc/kernel/Makefile
> +++ b/arch/sparc/kernel/Makefile
> @@ -7,8 +7,6 @@
>  asflags-y := -ansi
>  ccflags-y := -Werror
>  
> -extra-y     := head_$(BITS).o
> -
>  # Undefine sparc when processing vmlinux.lds - it is used
>  # And teach CPP we are doing $(BITS) builds (for this case)
>  CPPFLAGS_vmlinux.lds := -Usparc -m$(BITS)
> @@ -22,6 +20,7 @@ CFLAGS_REMOVE_perf_event.o := -pg
>  CFLAGS_REMOVE_pcr.o := -pg
>  endif
>  
> +obj-y                   := head_$(BITS).o
>  obj-$(CONFIG_SPARC64)   += urtt_fill.o
>  obj-$(CONFIG_SPARC32)   += entry.o wof.o wuf.o
>  obj-$(CONFIG_SPARC32)   += etrap_32.o
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index a20a5ebfacd7..956e50ca06e0 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -3,10 +3,6 @@
>  # Makefile for the linux kernel.
>  #
>  
> -extra-y	:= head_$(BITS).o
> -extra-y	+= head$(BITS).o
> -extra-y	+= ebda.o
> -extra-y	+= platform-quirks.o
>  extra-y	+= vmlinux.lds
>  
>  CPPFLAGS_vmlinux.lds += -U$(UTS_MACHINE)
> @@ -42,7 +38,11 @@ KCOV_INSTRUMENT		:= n
>  
>  CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace
>  
> -obj-y			:= process_$(BITS).o signal.o
> +obj-y			+= head_$(BITS).o
> +obj-y			+= head$(BITS).o
> +obj-y			+= ebda.o
> +obj-y			+= platform-quirks.o
> +obj-y			+= process_$(BITS).o signal.o
>  obj-$(CONFIG_COMPAT)	+= signal_compat.o
>  obj-y			+= traps.o idt.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
>  obj-y			+= time.o ioport.o dumpstack.o nmi.o
> diff --git a/arch/xtensa/kernel/Makefile b/arch/xtensa/kernel/Makefile
> index 897c1c741058..f28b8e3d717e 100644
> --- a/arch/xtensa/kernel/Makefile
> +++ b/arch/xtensa/kernel/Makefile
> @@ -3,9 +3,9 @@
>  # Makefile for the Linux/Xtensa kernel.
>  #
>  
> -extra-y := head.o vmlinux.lds
> +extra-y := vmlinux.lds
>  
> -obj-y := align.o coprocessor.o entry.o irq.o platform.o process.o \
> +obj-y := head.o align.o coprocessor.o entry.o irq.o platform.o process.o \
>  	 ptrace.o setup.o signal.o stacktrace.o syscall.o time.o traps.o \
>  	 vectors.o
>  
> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> index 2daf760eeb25..ceb1d78140e7 100644
> --- a/scripts/Makefile.modpost
> +++ b/scripts/Makefile.modpost
> @@ -70,13 +70,12 @@ quiet_cmd_vmlinux_objs = GEN     $@
>  	for f in $(real-prereqs); do	\
>  		case $${f} in		\
>  		*libgcc.a) ;;		\
> -		*.a) $(AR) t $${f} ;;	\
> -		*) echo $${f} ;;	\
> +		*) $(AR) t $${f} ;;	\
>  		esac			\
>  	done > $@
>  
>  targets += .vmlinux.objs
> -.vmlinux.objs: $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
> +.vmlinux.objs: vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
>  	$(call if_changed,vmlinux_objs)
>  
>  vmlinux.o-if-present := $(wildcard vmlinux.o)
> diff --git a/scripts/Makefile.vmlinux_o b/scripts/Makefile.vmlinux_o
> index 84019814f33f..81a4e0484457 100644
> --- a/scripts/Makefile.vmlinux_o
> +++ b/scripts/Makefile.vmlinux_o
> @@ -18,7 +18,7 @@ quiet_cmd_gen_initcalls_lds = GEN     $@
>  	$(PERL) $(real-prereqs) > $@
>  
>  .tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \
> -		$(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
> +		vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
>  	$(call if_changed,gen_initcalls_lds)
>  
>  targets := .tmp_initcalls.lds
> @@ -55,7 +55,7 @@ quiet_cmd_ld_vmlinux.o = LD      $@
>        cmd_ld_vmlinux.o = \
>  	$(LD) ${KBUILD_LDFLAGS} -r -o $@ \
>  	$(addprefix -T , $(initcalls-lds)) \
> -	--whole-archive $(KBUILD_VMLINUX_OBJS) --no-whole-archive \
> +	--whole-archive vmlinux.a --no-whole-archive \
>  	--start-group $(KBUILD_VMLINUX_LIBS) --end-group \
>  	$(cmd_objtool)
>  
> @@ -64,7 +64,7 @@ define rule_ld_vmlinux.o
>  	$(call cmd,gen_objtooldep)
>  endef
>  
> -vmlinux.o: $(initcalls-lds) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
> +vmlinux.o: $(initcalls-lds) vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
>  	$(call if_changed_rule,ld_vmlinux.o)
>  
>  targets += vmlinux.o
> diff --git a/scripts/clang-tools/gen_compile_commands.py b/scripts/clang-tools/gen_compile_commands.py
> index 47da25b3ba7d..d800b2c0af97 100755
> --- a/scripts/clang-tools/gen_compile_commands.py
> +++ b/scripts/clang-tools/gen_compile_commands.py
> @@ -109,20 +109,6 @@ def to_cmdfile(path):
>      return os.path.join(dir, '.' + base + '.cmd')
>  
>  
> -def cmdfiles_for_o(obj):
> -    """Generate the iterator of .cmd files associated with the object
> -
> -    Yield the .cmd file used to build the given object
> -
> -    Args:
> -        obj: The object path
> -
> -    Yields:
> -        The path to .cmd file
> -    """
> -    yield to_cmdfile(obj)
> -
> -
>  def cmdfiles_for_a(archive, ar):
>      """Generate the iterator of .cmd files associated with the archive.
>  
> @@ -211,13 +197,10 @@ def main():
>      for path in paths:
>          # If 'path' is a directory, handle all .cmd files under it.
>          # Otherwise, handle .cmd files associated with the file.
> -        # Most of built-in objects are linked via archives (built-in.a or lib.a)
> -        # but some objects are linked to vmlinux directly.
> +        # built-in objects are linked via vmlinux.a
>          # Modules are listed in modules.order.
>          if os.path.isdir(path):
>              cmdfiles = cmdfiles_in_dir(path)
> -        elif path.endswith('.o'):
> -            cmdfiles = cmdfiles_for_o(path)
>          elif path.endswith('.a'):
>              cmdfiles = cmdfiles_for_a(path, ar)
>          elif path.endswith('modules.order'):
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 6a197d8a88ac..23ac13fd9d89 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -3,17 +3,15 @@
>  #
>  # link vmlinux
>  #
> -# vmlinux is linked from the objects selected by $(KBUILD_VMLINUX_OBJS) and
> -# $(KBUILD_VMLINUX_LIBS). Most are built-in.a files from top-level directories
> -# in the kernel tree, others are specified in arch/$(ARCH)/Makefile.
> +# vmlinux is linked from the objects in vmlinux.a and $(KBUILD_VMLINUX_LIBS).
> +# vmlinux.a contains objects that are linked unconditionally.
>  # $(KBUILD_VMLINUX_LIBS) are archives which are linked conditionally
>  # (not within --whole-archive), and do not require symbol indexes added.
>  #
>  # vmlinux
>  #   ^
>  #   |
> -#   +--< $(KBUILD_VMLINUX_OBJS)
> -#   |    +--< init/built-in.a drivers/built-in.a mm/built-in.a + more
> +#   +--< vmlinux.a
>  #   |
>  #   +--< $(KBUILD_VMLINUX_LIBS)
>  #   |    +--< lib/lib.a + more
> @@ -67,7 +65,7 @@ vmlinux_link()
>  		objs=vmlinux.o
>  		libs=
>  	else
> -		objs="${KBUILD_VMLINUX_OBJS}"
> +		objs=vmlinux.a
>  		libs="${KBUILD_VMLINUX_LIBS}"
>  	fi
>  
> -- 
> 2.34.1

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Patchew 2.1-devel-ea86937

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