[v1] Start porting UML to nolibc

[PATCH 7/9] um: add infrastructure to build files using nolibc

Posted by Benjamin Berg 2 weeks, 3 days ago

From: Benjamin Berg <benjamin.berg@intel.com>

Add NOLIBC_CFLAGS and NOLIBC_OBJS to build files against nolibc rather
than libc. With this it is possible to move to nolibc in smaller steps.

Set NOLIBC_IGNORE_ERRNO, as the nolibc errno implementation is overly
simple and cannot handle threading. nolibc provides sys_* functions that
do not emulate the libc errno behaviour and can be used instead.

Guard the syscall definition as it is a macro in nolibc.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
---
 arch/um/Makefile               | 21 ++++++++++++++++++++-
 arch/um/include/shared/os.h    |  2 ++
 arch/um/scripts/Makefile.rules |  8 +++++++-
 3 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/arch/um/Makefile b/arch/um/Makefile
index a3f27d791cc0..54aa26fcc32b 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -78,6 +78,25 @@ USER_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \
 		-include $(srctree)/include/linux/kern_levels.h \
 		-include $(srctree)/$(ARCH_DIR)/include/shared/user.h
 
+NOLIBC_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \
+		$(ARCH_INCLUDE) $(MODE_INCLUDE) $(filter -I%,$(CFLAGS)) \
+		-I $(srctree)/tools/include \
+		-D__EXPORTED_HEADERS__ \
+		-D__UM_HOST__ -D__UM_NOLIBC__ \
+		-DNOLIBC_NO_STARTCODE \
+		-DNOLIBC_IGNORE_ERRNO \
+		-nostdlib -nostdinc -static \
+		-I$(srctree)/include/uapi \
+		-I$(srctree)/$(HOST_DIR)/include/uapi \
+		-I$(objtree)/$(HOST_DIR)/include/generated/uapi \
+		-I $(srctree)/tools/include/nolibc \
+		-I $(srctree)/usr/include \
+		-include $(srctree)/include/generated/autoconf.h \
+		-include $(srctree)/tools/include/linux/kconfig.h \
+		-include $(srctree)/include/linux/kern_levels.h \
+		-include $(srctree)/tools/include/nolibc/nolibc.h \
+		-include $(srctree)/$(ARCH_DIR)/include/shared/user.h
+
 #This will adjust *FLAGS accordingly to the platform.
 include $(srctree)/$(ARCH_DIR)/Makefile-os-Linux
 
@@ -157,4 +176,4 @@ archclean:
 		-o -name '*.gcov' \) -type f -print | xargs rm -f
 	$(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(HEADER_ARCH) clean
 
-export HEADER_ARCH SUBARCH USER_CFLAGS CFLAGS_NO_HARDENING DEV_NULL_PATH
+export HEADER_ARCH SUBARCH USER_CFLAGS NOLIBC_CFLAGS CFLAGS_NO_HARDENING DEV_NULL_PATH
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index b35cc8ce333b..3e9f3ae61658 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -327,7 +327,9 @@ extern int __ignore_sigio_fd(int fd);
 /* tty.c */
 extern int get_pty(void);
 
+#ifndef syscall
 long syscall(long number, ...);
+#endif
 
 /* irqflags tracing */
 extern void block_signals_trace(void);
diff --git a/arch/um/scripts/Makefile.rules b/arch/um/scripts/Makefile.rules
index b4a2e0058503..5f07551935c3 100644
--- a/arch/um/scripts/Makefile.rules
+++ b/arch/um/scripts/Makefile.rules
@@ -11,6 +11,12 @@ USER_OBJS := $(foreach file,$(USER_OBJS),$(obj)/$(file))
 $(USER_OBJS:.o=.%): \
 	c_flags = -Wp,-MD,$(depfile) $(USER_CFLAGS) $(CFLAGS_$(basetarget).o)
 
+# Similar USER_OBJS but compiled against nolibc (may include kernel headers?)
+NOLIBC_OBJS := $(foreach file,$(NOLIBC_OBJS),$(obj)/$(file))
+
+$(NOLIBC_OBJS:.o=.%): \
+	c_flags = -Wp,-MD,$(depfile) $(NOLIBC_CFLAGS) $(CFLAGS_$(basetarget).o)
+
 # These are like USER_OBJS but filter USER_CFLAGS through unprofile instead of
 # using it directly.
 UNPROFILE_OBJS := $(foreach file,$(UNPROFILE_OBJS),$(obj)/$(file))
@@ -18,7 +24,7 @@ UNPROFILE_OBJS := $(foreach file,$(UNPROFILE_OBJS),$(obj)/$(file))
 $(UNPROFILE_OBJS:.o=.%): \
 	c_flags = -Wp,-MD,$(depfile) $(call unprofile,$(USER_CFLAGS)) $(CFLAGS_$(basetarget).o)
 
-$(USER_OBJS) $(UNPROFILE_OBJS): \
+$(USER_OBJS) $(NOLIBC_OBJS) $(UNPROFILE_OBJS): \
 	CHECKFLAGS := $(patsubst $(NOSTDINC_FLAGS),,$(CHECKFLAGS))
 
 # The stubs can't try to call mcount or update basic block data
-- 
2.51.0

Re: [PATCH 7/9] um: add infrastructure to build files using nolibc

Posted by Thomas Weißschuh 2 weeks, 3 days ago

On 2025-09-15 09:11:13+0200, Benjamin Berg wrote:
> From: Benjamin Berg <benjamin.berg@intel.com>
> 
> Add NOLIBC_CFLAGS and NOLIBC_OBJS to build files against nolibc rather
> than libc. With this it is possible to move to nolibc in smaller steps.
> 
> Set NOLIBC_IGNORE_ERRNO, as the nolibc errno implementation is overly
> simple and cannot handle threading. nolibc provides sys_* functions that
> do not emulate the libc errno behaviour and can be used instead.
> 
> Guard the syscall definition as it is a macro in nolibc.
> 
> Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
> ---
>  arch/um/Makefile               | 21 ++++++++++++++++++++-
>  arch/um/include/shared/os.h    |  2 ++
>  arch/um/scripts/Makefile.rules |  8 +++++++-
>  3 files changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/um/Makefile b/arch/um/Makefile
> index a3f27d791cc0..54aa26fcc32b 100644
> --- a/arch/um/Makefile
> +++ b/arch/um/Makefile
> @@ -78,6 +78,25 @@ USER_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \
>  		-include $(srctree)/include/linux/kern_levels.h \
>  		-include $(srctree)/$(ARCH_DIR)/include/shared/user.h
>  
> +NOLIBC_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \
> +		$(ARCH_INCLUDE) $(MODE_INCLUDE) $(filter -I%,$(CFLAGS)) \
> +		-I $(srctree)/tools/include \
> +		-D__EXPORTED_HEADERS__ \
> +		-D__UM_HOST__ -D__UM_NOLIBC__ \
> +		-DNOLIBC_NO_STARTCODE \
> +		-DNOLIBC_IGNORE_ERRNO \
> +		-nostdlib -nostdinc -static \
> +		-I$(srctree)/include/uapi \
> +		-I$(srctree)/$(HOST_DIR)/include/uapi \
> +		-I$(objtree)/$(HOST_DIR)/include/generated/uapi \
> +		-I $(srctree)/tools/include/nolibc \
> +		-I $(srctree)/usr/include \
> +		-include $(srctree)/include/generated/autoconf.h \
> +		-include $(srctree)/tools/include/linux/kconfig.h \
> +		-include $(srctree)/include/linux/kern_levels.h \
> +		-include $(srctree)/tools/include/nolibc/nolibc.h \

This is not needed. It doesn't hurt though.

> +		-include $(srctree)/$(ARCH_DIR)/include/shared/user.h
> +
>  #This will adjust *FLAGS accordingly to the platform.
>  include $(srctree)/$(ARCH_DIR)/Makefile-os-Linux
>  
> @@ -157,4 +176,4 @@ archclean:
>  		-o -name '*.gcov' \) -type f -print | xargs rm -f
>  	$(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(HEADER_ARCH) clean
>  
> -export HEADER_ARCH SUBARCH USER_CFLAGS CFLAGS_NO_HARDENING DEV_NULL_PATH
> +export HEADER_ARCH SUBARCH USER_CFLAGS NOLIBC_CFLAGS CFLAGS_NO_HARDENING DEV_NULL_PATH
> diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
> index b35cc8ce333b..3e9f3ae61658 100644
> --- a/arch/um/include/shared/os.h
> +++ b/arch/um/include/shared/os.h
> @@ -327,7 +327,9 @@ extern int __ignore_sigio_fd(int fd);
>  /* tty.c */
>  extern int get_pty(void);
>  
> +#ifndef syscall

You could use 'ifndef NOLIBC' to make the reason clear.

>  long syscall(long number, ...);
> +#endif
>  
>  /* irqflags tracing */
>  extern void block_signals_trace(void);

(...)