| Message ID | 20200629085911.1676554-1-masahiroy@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: make Clang build userprogs for target architecture | expand |
On Mon, Jun 29, 2020 at 1:59 AM Masahiro Yamada <masahiroy@kernel.org> wrote: > > Programs added 'userprogs' should be compiled for the target > architecture i.e. the same architecture as the kernel. > > GCC does this correctly since the target architecture is implied > by the toolchain prefix. > > Clang builds standalone programs always for the host architecture > because the target triple is currently missing. > > Fix this. > > Fixes: 7f3a59db274c ("kbuild: add infrastructure to build userspace programs") This is a neat feature I didn't know about; looks relatively new. What's the test case command line invocation to test this with Clang? > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> > --- > > Makefile | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/Makefile b/Makefile > index 73948798ce3f..cac29cc2ec25 100644 > --- a/Makefile > +++ b/Makefile > @@ -970,8 +970,8 @@ LDFLAGS_vmlinux += --pack-dyn-relocs=relr > endif > > # Align the bit size of userspace programs with the kernel > -KBUILD_USERCFLAGS += $(filter -m32 -m64, $(KBUILD_CFLAGS)) > -KBUILD_USERLDFLAGS += $(filter -m32 -m64, $(KBUILD_CFLAGS)) > +KBUILD_USERCFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS)) > +KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS)) That should be fine. Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> https://www.gnu.org/software/make/manual/html_node/Text-Functions.html > > # make the checker run with the right architecture > CHECKFLAGS += --arch=$(ARCH) > --
On Tue, Jun 30, 2020 at 2:39 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Mon, Jun 29, 2020 at 1:59 AM Masahiro Yamada <masahiroy@kernel.org> wrote: > > > > Programs added 'userprogs' should be compiled for the target > > architecture i.e. the same architecture as the kernel. > > > > GCC does this correctly since the target architecture is implied > > by the toolchain prefix. > > > > Clang builds standalone programs always for the host architecture > > because the target triple is currently missing. > > > > Fix this. > > > > Fixes: 7f3a59db274c ("kbuild: add infrastructure to build userspace programs") > > This is a neat feature I didn't know about; looks relatively new. > What's the test case command line invocation to test this with Clang? Test command: $ make -j24 ARCH=arm LLVM=1 CROSS_COMPILE=arm-linux-gnueabi- allyesconfig samples/ [ snip ] CC [U] samples/watch_queue/watch_test CC [U] samples/timers/hpet_example CC [U] samples/vfs/test-fsmount CC [U] samples/binderfs/binderfs_example CC [U] samples/auxdisplay/cfag12864b-example CC [U] samples/hidraw/hid-example CC [U] samples/uhid/uhid-example CC [U] samples/connector/ucon CC [U] samples/watchdog/watchdog-simple CC [U] samples/vfs/test-statx Then, check if the sample programs were correctly built for ARM. Before this commit: $ file samples/vfs/test-statx samples/vfs/test-statx: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, not stripped After this commit: $ file samples/vfs/test-statx samples/vfs/test-statx: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.3, for GNU/Linux 3.2.0, not stripped To test this, having LLVM is not enough because building userspace programs requires target-specific libraries. As for GCC, libc is usually bundled together with toolchains, but as for LLVM we need to provide target-specific libc. This introduces a different kind of complexity than building the kernel. I read this article: https://clang.llvm.org/docs/CrossCompilation.html I use tc-build to compile llvm from source code, but I also needed to install ARM libc. "apt install gcc-arm-linux-gnueabi" especially "apt install libc6-dev-armel-cross". If I build sample code for ARCH=arm64, I see the following warnings. $ make -j24 ARCH=arm64 LLVM=1 CROSS_COMPILE=aarch64-linux-gnu- allyesconfig samples/ [ snip ] CC [U] samples/uhid/uhid-example samples/uhid/uhid-example.c:169:4: warning: format specifies type 'ssize_t' (aka 'long') but the argument has type 'ssize_t' (aka 'int') [-Wformat] ret, sizeof(ev)); ^~~ samples/uhid/uhid-example.c:240:4: warning: format specifies type 'ssize_t' (aka 'long') but the argument has type 'ssize_t' (aka 'int') [-Wformat] ret, sizeof(ev)); ^~~ 2 warnings generated. CC [U] samples/vfs/test-fsmount CC [U] samples/vfs/test-statx CC [U] samples/watch_queue/watch_test samples/watch_queue/watch_test.c:86:50: warning: format specifies type 'ssize_t' (aka 'long') but the argument has type 'ssize_t' (aka 'int') [-Wformat] fprintf(stderr, "Read buffer overrun: %zd\n", buf_len); ~~~ ^~~~~~~ %d samples/watch_queue/watch_test.c:90:28: warning: format specifies type 'ssize_t' (aka 'long') but the argument has type 'ssize_t' (aka 'int') [-Wformat] printf("read() = %zd\n", buf_len); ~~~ ^~~~~~~ %d 2 warnings generated. CC [U] samples/watchdog/watchdog-simple AR samples/built-in.a I do not know how to solve this issue. I can reproduce this in the following simple test code: ----------------->8---------------- #include <stdio.h> int main(void) { ssize_t x = 1; printf("%zd", x); return 0; } --------------->8------------------- $ clang --target=aarch64-linux-gnu test.c test.c:7:16: warning: format specifies type 'ssize_t' (aka 'long') but the argument has type 'ssize_t' (aka 'int') [-Wformat] printf("%zd", x); ~~~ ^ %zd 1 warning generated. ssize_t is defined in /usr/include/stdio.h but perhaps this is not suitable for cross-compilation for aarch64. Is there any solution? > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> > > --- > > > > Makefile | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/Makefile b/Makefile > > index 73948798ce3f..cac29cc2ec25 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -970,8 +970,8 @@ LDFLAGS_vmlinux += --pack-dyn-relocs=relr > > endif > > > > # Align the bit size of userspace programs with the kernel > > -KBUILD_USERCFLAGS += $(filter -m32 -m64, $(KBUILD_CFLAGS)) > > -KBUILD_USERLDFLAGS += $(filter -m32 -m64, $(KBUILD_CFLAGS)) > > +KBUILD_USERCFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS)) > > +KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS)) > > That should be fine. > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > https://www.gnu.org/software/make/manual/html_node/Text-Functions.html > > > > > # make the checker run with the right architecture > > CHECKFLAGS += --arch=$(ARCH) > > -- > > > -- > Thanks, > ~Nick Desaulniers
On Tue, Jun 30, 2020 at 6:26 PM Masahiro Yamada <masahiroy@kernel.org> wrote: > > I can reproduce this in the following > simple test code: > > > ----------------->8---------------- > #include <stdio.h> > > int main(void) > { > ssize_t x = 1; > > printf("%zd", x); > > return 0; > } > --------------->8------------------- That is the old implicit int rule. Try including sys/types.h or compiling with a standard like -std=c99 for instance. Cheers, Miguel
On Wed, Jul 1, 2020 at 4:13 AM Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote: > > On Tue, Jun 30, 2020 at 6:26 PM Masahiro Yamada <masahiroy@kernel.org> wrote: > > > > I can reproduce this in the following > > simple test code: > > > > > > ----------------->8---------------- > > #include <stdio.h> > > > > int main(void) > > { > > ssize_t x = 1; > > > > printf("%zd", x); > > > > return 0; > > } > > --------------->8------------------- > > That is the old implicit int rule. Try including sys/types.h or > compiling with a standard like -std=c99 for instance. > > Cheers, > Miguel Hmm, adding '#include <sys/types.h>' did not make any difference. If I add -std=c99, I get a different error. $ clang -std=c99 --target=aarch64-linux-gnu test.c test.c:5:10: error: unknown type name 'ssize_t'; did you mean 'size_t'? ssize_t x = 1; ^~~~~~~ size_t /home/masahiro/tools/clang-latest/lib/clang/11.0.0/include/stddef.h:46:23: note: 'size_t' declared here typedef __SIZE_TYPE__ size_t; ^ 1 error generated. In contrast, 'size_t' has no problem. ----------------->8---------------- #include <stdio.h> int main(void) { size_t x = 1; printf("%zu", x); return 0; } --------------->8------------------- $ clang --target=aarch64-linux-gnu test.c [ No warning ] -- Best Regards Masahiro Yamada
Hi Masahiro, On Sun, Jul 5, 2020 at 5:30 PM Masahiro Yamada <masahiroy@kernel.org> wrote: > > Hmm, adding '#include <sys/types.h>' did not make any difference. That should have worked, because POSIX defines it to be there. It sounds like you need --sysroot to point it to the proper ones. > If I add -std=c99, I get a different error. Yeah, that is the expected behavior. C99 does not have the implicit int rule anymore (unlike older C) so ssize_t (an unknown type given that program) is not being interpreted as int anymore (which is what triggers the warning later about the mismatch between size_t and int in the format string). > In contrast, 'size_t' has no problem. That is expected too, because size_t is defined via stdio.h (size_t is a C standard type, ssize_t is not -- it is a POSIX one). Hope that helps, Cheers, Miguel
diff --git a/Makefile b/Makefile index 73948798ce3f..cac29cc2ec25 100644 --- a/Makefile +++ b/Makefile @@ -970,8 +970,8 @@ LDFLAGS_vmlinux += --pack-dyn-relocs=relr endif # Align the bit size of userspace programs with the kernel -KBUILD_USERCFLAGS += $(filter -m32 -m64, $(KBUILD_CFLAGS)) -KBUILD_USERLDFLAGS += $(filter -m32 -m64, $(KBUILD_CFLAGS)) +KBUILD_USERCFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS)) +KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS)) # make the checker run with the right architecture CHECKFLAGS += --arch=$(ARCH)
Programs added 'userprogs' should be compiled for the target architecture i.e. the same architecture as the kernel. GCC does this correctly since the target architecture is implied by the toolchain prefix. Clang builds standalone programs always for the host architecture because the target triple is currently missing. Fix this. Fixes: 7f3a59db274c ("kbuild: add infrastructure to build userspace programs") Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> --- Makefile | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)