Messages in this thread | | | Date | Thu, 27 Jan 2022 19:15:49 -0800 | From | Fangrui Song <> | Subject | Re: [PATCH] kbuild: Add environment variables for userprogs flags |
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On 2022-01-26, Nick Desaulniers wrote: >On Wed, Jan 12, 2022 at 2:44 PM Elliot Berman <quic_eberman@quicinc.com> wrote: >> >> Allow additional arguments be passed to userprogs compilation. >> Reproducible clang builds need to provide a sysroot and gcc path to >> ensure same toolchain is used across hosts. KCFLAGS is not currently >> used for any user programs compilation, so add new USERCFLAGS and >> USERLDFLAGS which serves similar purpose as HOSTCFLAGS/HOSTLDFLAGS. >> >> Specifically, I'm trying to force CC_CAN_LINK to consistently fail in >> an environment where a user sysroot is not specifically available. >> Currently, Clang might automatically detect GCC installation on hosts >> which have it installed to a default location in /. With addition of >> these environment variables, our build environment can do like >> "--sysroot=/dev/null" to force sysroot detection to fail. > >Hi Elliot, >Thanks for the patch! Sorry for the delay in reviewing; I didn't quite >get around to it then went on vacation for a week. Things get buried >in my inbox quickly; feel free to ping me if a week goes by with no >response on whichever channel works best for you. > >I'm happy with the intent of this patch; GNU binutils has been removed >from Android, so supporting CC_CAN_LINK for Android kernel builds has >been a question I've been thinking about (though, not with higher >priority with some of our other issues), since we'll need to either >incorporate musl or bionic libc into our kernel build. I was thinking >of adding a SYSROOT command line variable for that, but I see your >approach is more flexible. > >One minor nit below, a typo, a few questions, and in the commit >message, but this generally LGTM. > >For the commit message, I think it would be good to expand `can do >like "--sysroot=/dev/null"` fully into >``` >can specify >$ make USERCFLAGS=--sysroot=/dev/null USERLDFLAGS=-Wl,--sysroot=/dev/null >```
Is -Wl,--sysroot=/dev/null to override a -Wl,--sysroot specified previously on the command line?
The driver option --sysroot does two things:
* Decide include/library search paths (e.g. $sysroot/usr/include, $sysroot/lib64). * Pass --sysroot to ld.
In ld, it means: if a linker script is in the sysroot directory, when ld opens an absolute path file (via INPUT or GROUP), add sysroot before the absolute path. In ld, --sysroot=/dev/null is not different --sysroot= (empty value).
>> >> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com> >> --- >> Documentation/kbuild/kbuild.rst | 8 ++++++++ >> Makefile | 9 ++++++--- >> init/Kconfig | 8 ++++---- >> usr/include/Makefile | 3 +++ >> 4 files changed, 21 insertions(+), 7 deletions(-) >> >> diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst >> index 2d1fc03d346e..16e90a3ae01b 100644 >> --- a/Documentation/kbuild/kbuild.rst >> +++ b/Documentation/kbuild/kbuild.rst >> @@ -77,6 +77,14 @@ HOSTLDLIBS >> ---------- >> Additional libraries to link against when building host programs. >> >> +USERCFLAGS >> +---------- >> +Additional options used for $(CC) when compiling userprogs. >> + >> +USERLDFLAGS >> +---------- >> +Additional options used for $(LD) when linking userprogs. > >Probably should note the necessity of `-Wl,` prefixes here. > >Is `userprogs` cannonical? Yeah, I guess (reading >Documentation/kbuild/makefiles.rst). I wonder if we should mention >these in Documentation/kbuild/makefiles.rst as well? Under `5.3 >Controlling compiler options for userspace programs`. > >> + >> KBUILD_KCONFIG >> -------------- >> Set the top-level Kconfig file to the value of this environment >> diff --git a/Makefile b/Makefile >> index 45278d508d81..4a55537c8ca0 100644 >> --- a/Makefile >> +++ b/Makefile >> @@ -431,15 +431,17 @@ HOSTCC = gcc >> HOSTCXX = g++ >> endif >> >> -export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \ >> - -O2 -fomit-frame-pointer -std=gnu89 >> -export KBUILD_USERLDFLAGS := >> +KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \ >> + -O2 -fomit-frame-pointer -std=gnu89 >> +KBUILD_USERLDFLAGS := $(USERLDFLAGGS) > >^ I think there's an extra G in USERLDFLAGS above. > >> >> KBUILD_HOSTCFLAGS := $(KBUILD_USERCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS) >> KBUILD_HOSTCXXFLAGS := -Wall -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS) >> KBUILD_HOSTLDFLAGS := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS) >> KBUILD_HOSTLDLIBS := $(HOST_LFS_LIBS) $(HOSTLDLIBS) >> >> +KBUILD_USERCFLAGS += $(USERCFLAGS) > >Since you added USERLDFLAGS to KBUILD_USERLDFLAGS above where it's >defined, why not do so for USERCFLAGS/KBUILD_USERCFLAGS as well? > >> + >> # Make variables (CC, etc...) >> CPP = $(CC) -E >> ifneq ($(LLVM),) >> @@ -530,6 +532,7 @@ export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX YACC AW >> export PERL PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX >> export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD >> export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE >> +export KBUILD_USERCFLAGS KBUILD_USERLDFLAGS >> >> export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS >> export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE >> diff --git a/init/Kconfig b/init/Kconfig >> index f2ae41e6717f..164706c38e8b 100644 >> --- a/init/Kconfig >> +++ b/init/Kconfig >> @@ -62,13 +62,13 @@ config LLD_VERSION >> >> config CC_CAN_LINK >> bool >> - default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT >> - default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag)) >> + default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag)) if 64BIT >> + default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag)) >> >> config CC_CAN_LINK_STATIC >> bool >> - default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag) -static) if 64BIT >> - default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag) -static) >> + default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT >> + default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag) -static) > >since USERLDFLAGS get passed to $(CC), they will need `-Wl`, prefixes, >hence the request for expanding the example usage in the commit >message. > >> >> config CC_HAS_ASM_GOTO >> def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC)) >> diff --git a/usr/include/Makefile b/usr/include/Makefile >> index 1c2ae1368079..6a8c7dd9ccaf 100644 >> --- a/usr/include/Makefile >> +++ b/usr/include/Makefile >> @@ -12,6 +12,9 @@ UAPI_CFLAGS := -std=c90 -Wall -Werror=implicit-function-declaration >> # It is here just because CONFIG_CC_CAN_LINK is tested with -m32 or -m64. >> UAPI_CFLAGS += $(filter -m32 -m64, $(KBUILD_CFLAGS)) >> >> +# USERCFLAGS might contain sysroot location for CC >> +UAPI_CFLAGS += $(USERCFLAGS) >> + > >Do we need to worry about USERLDFLAGS here, too? (or usr/Makefile?) > >> override c_flags = $(UAPI_CFLAGS) -Wp,-MMD,$(depfile) -I$(objtree)/usr/include >> >> # The following are excluded for now because they fail to build. >> -- >> 2.25.1 >> > > >-- >Thanks, >~Nick Desaulniers
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