If explicit relocation hints is used by the toolchain, -Wa,-mla-*
options will be useless for C code. Only use them for
!CONFIG_AS_HAS_EXPLICIT_RELOCS.
Replace "la" with "la.pcrel" in head.S to keep the semantic consistent
with new and old toolchains for the low level startup code.
Remove -fplt because it's the default for all known LoongArch C
compilers.
The behavior with different assemblers and compilers are summarized in
the following table:
AS has CC has
explicit reloc explicit reloc Behavior
==============================================================
No No Use la.* macros.
No change from Linux 6.0.
--------------------------------------------------------------
No Yes Disable explicit reloc.
No change from Linux 6.0.
--------------------------------------------------------------
Yes No Not supported.
--------------------------------------------------------------
Yes Yes Use explicit relocs.
No -Wa,-mla* options.
==============================================================
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
---
arch/loongarch/Makefile | 19 ++++++++++++++++++-
arch/loongarch/kernel/head.S | 10 +++++-----
2 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index 7051a95f7f31..1563747c4fa8 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -40,10 +40,27 @@ endif
cflags-y += -G0 -pipe -msoft-float
LDFLAGS_vmlinux += -G0 -static -n -nostdlib
+
+# When the assembler supports explicit relocation hint, we must use it.
+# GCC may have -mexplicit-relocs off by default if it was built with an old
+# assembler, so we force it via an option.
+#
+# When the assembler does not supports explicit relocation hint, we can't use
+# it. Disable it if the compiler supports it.
+#
+# If you've seen "unknown reloc hint" message building the kernel and you are
+# now wondering why "-mexplicit-relocs" is not wrapped with cc-option: the
+# combination of a "new" assembler and "old" compiler is not supported. Either
+# upgrade the compiler or downgrade the assembler.
+ifdef CONFIG_AS_HAS_EXPLICIT_RELOCS
+cflags-y += -mexplicit-relocs
+else
+cflags-y += $(call cc-option,-mno-explicit-relocs)
KBUILD_AFLAGS_KERNEL += -Wa,-mla-global-with-pcrel
KBUILD_CFLAGS_KERNEL += -Wa,-mla-global-with-pcrel
KBUILD_AFLAGS_MODULE += -Wa,-mla-global-with-abs
-KBUILD_CFLAGS_MODULE += -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs
+KBUILD_CFLAGS_MODULE += -Wa,-mla-global-with-abs,-mla-local-with-abs
+endif
cflags-y += -ffreestanding
cflags-y += $(call cc-option, -mno-check-zero-division)
diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
index 01bac62a6442..eb3f641d5915 100644
--- a/arch/loongarch/kernel/head.S
+++ b/arch/loongarch/kernel/head.S
@@ -55,17 +55,17 @@ SYM_CODE_START(kernel_entry) # kernel entry point
li.w t0, 0x00 # FPE=0, SXE=0, ASXE=0, BTE=0
csrwr t0, LOONGARCH_CSR_EUEN
- la t0, __bss_start # clear .bss
+ la.pcrel t0, __bss_start # clear .bss
st.d zero, t0, 0
- la t1, __bss_stop - LONGSIZE
+ la.pcrel t1, __bss_stop - LONGSIZE
1:
addi.d t0, t0, LONGSIZE
st.d zero, t0, 0
bne t0, t1, 1b
- la t0, fw_arg0
+ la.pcrel t0, fw_arg0
st.d a0, t0, 0 # firmware arguments
- la t0, fw_arg1
+ la.pcrel t0, fw_arg1
st.d a1, t0, 0
/* KSave3 used for percpu base, initialized as 0 */
@@ -73,7 +73,7 @@ SYM_CODE_START(kernel_entry) # kernel entry point
/* GPR21 used for percpu base (runtime), initialized as 0 */
move u0, zero
- la tp, init_thread_union
+ la.pcrel tp, init_thread_union
/* Set the SP after an empty pt_regs. */
PTR_LI sp, (_THREAD_SIZE - 32 - PT_SIZE)
PTR_ADD sp, sp, tp
--
2.37.0Hi, Ruoyao, On Mon, Aug 29, 2022 at 9:35 PM Xi Ruoyao <xry111@xry111.site> wrote: > > If explicit relocation hints is used by the toolchain, -Wa,-mla-* > options will be useless for C code. Only use them for > !CONFIG_AS_HAS_EXPLICIT_RELOCS. > > Replace "la" with "la.pcrel" in head.S to keep the semantic consistent > with new and old toolchains for the low level startup code. > > Remove -fplt because it's the default for all known LoongArch C > compilers. > > The behavior with different assemblers and compilers are summarized in > the following table: > > AS has CC has > explicit reloc explicit reloc Behavior > ============================================================== > No No Use la.* macros. > No change from Linux 6.0. > -------------------------------------------------------------- > No Yes Disable explicit reloc. > No change from Linux 6.0. > -------------------------------------------------------------- > Yes No Not supported. > -------------------------------------------------------------- > Yes Yes Use explicit relocs. > No -Wa,-mla* options. > ============================================================== > > Signed-off-by: Xi Ruoyao <xry111@xry111.site> > --- > arch/loongarch/Makefile | 19 ++++++++++++++++++- > arch/loongarch/kernel/head.S | 10 +++++----- > 2 files changed, 23 insertions(+), 6 deletions(-) > > diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile > index 7051a95f7f31..1563747c4fa8 100644 > --- a/arch/loongarch/Makefile > +++ b/arch/loongarch/Makefile > @@ -40,10 +40,27 @@ endif > > cflags-y += -G0 -pipe -msoft-float > LDFLAGS_vmlinux += -G0 -static -n -nostdlib > + > +# When the assembler supports explicit relocation hint, we must use it. > +# GCC may have -mexplicit-relocs off by default if it was built with an old > +# assembler, so we force it via an option. > +# > +# When the assembler does not supports explicit relocation hint, we can't use > +# it. Disable it if the compiler supports it. > +# > +# If you've seen "unknown reloc hint" message building the kernel and you are > +# now wondering why "-mexplicit-relocs" is not wrapped with cc-option: the > +# combination of a "new" assembler and "old" compiler is not supported. Either > +# upgrade the compiler or downgrade the assembler. > +ifdef CONFIG_AS_HAS_EXPLICIT_RELOCS > +cflags-y += -mexplicit-relocs > +else > +cflags-y += $(call cc-option,-mno-explicit-relocs) > KBUILD_AFLAGS_KERNEL += -Wa,-mla-global-with-pcrel > KBUILD_CFLAGS_KERNEL += -Wa,-mla-global-with-pcrel > KBUILD_AFLAGS_MODULE += -Wa,-mla-global-with-abs > -KBUILD_CFLAGS_MODULE += -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs > +KBUILD_CFLAGS_MODULE += -Wa,-mla-global-with-abs,-mla-local-with-abs Though -fplt is the default, keep it can make code clearer. Huacai > +endif > > cflags-y += -ffreestanding > cflags-y += $(call cc-option, -mno-check-zero-division) > diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S > index 01bac62a6442..eb3f641d5915 100644 > --- a/arch/loongarch/kernel/head.S > +++ b/arch/loongarch/kernel/head.S > @@ -55,17 +55,17 @@ SYM_CODE_START(kernel_entry) # kernel entry point > li.w t0, 0x00 # FPE=0, SXE=0, ASXE=0, BTE=0 > csrwr t0, LOONGARCH_CSR_EUEN > > - la t0, __bss_start # clear .bss > + la.pcrel t0, __bss_start # clear .bss > st.d zero, t0, 0 > - la t1, __bss_stop - LONGSIZE > + la.pcrel t1, __bss_stop - LONGSIZE > 1: > addi.d t0, t0, LONGSIZE > st.d zero, t0, 0 > bne t0, t1, 1b > > - la t0, fw_arg0 > + la.pcrel t0, fw_arg0 > st.d a0, t0, 0 # firmware arguments > - la t0, fw_arg1 > + la.pcrel t0, fw_arg1 > st.d a1, t0, 0 > > /* KSave3 used for percpu base, initialized as 0 */ > @@ -73,7 +73,7 @@ SYM_CODE_START(kernel_entry) # kernel entry point > /* GPR21 used for percpu base (runtime), initialized as 0 */ > move u0, zero > > - la tp, init_thread_union > + la.pcrel tp, init_thread_union > /* Set the SP after an empty pt_regs. */ > PTR_LI sp, (_THREAD_SIZE - 32 - PT_SIZE) > PTR_ADD sp, sp, tp > -- > 2.37.0 > >
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