Re: [PATCH bpf-next v2 0/5] bpf: tools: support build selftests/bpf with clang

[Jiri Olsa <jolsa@redhat.com>]

On Tue, Apr 13, 2021 at 11:56:33AM -0700, Nick Desaulniers wrote:
> On Tue, Apr 13, 2021 at 11:46 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Mon, Apr 12, 2021 at 5:31 PM Yonghong Song <yhs@fb.com> wrote:
> > >
> > >
> > >
> > > On 4/12/21 5:02 PM, Nick Desaulniers wrote:
> > > > On Mon, Apr 12, 2021 at 4:58 PM Nick Desaulniers
> > > > <ndesaulniers@google.com> wrote:
> > > >>
> > > >> On Mon, Apr 12, 2021 at 7:29 AM Yonghong Song <yhs@fb.com> wrote:
> > > >>>
> > > >>> To build kernel with clang, people typically use
> > > >>>    make -j60 LLVM=1 LLVM_IAS=1
> > > >>> LLVM_IAS=1 is not required for non-LTO build but
> > > >>> is required for LTO build. In my environment,
> > > >>> I am always having LLVM_IAS=1 regardless of
> > > >>> whether LTO is enabled or not.
> > > >>>
> > > >>> After kernel is build with clang, the following command
> > > >>> can be used to build selftests with clang:
> > > >>>    make -j60 -C tools/testing/selftests/bpf LLVM=1 LLVM_IAS=1
> > > >>
> > > >> Thank you for the series Yonghong.  When I test the above command with
> > > >> your series applied, I observe:
> > > >> tools/include/tools/libc_compat.h:11:21: error: static declaration of
> > > >> 'reallocarray' follows non-static declaration
> > > >> static inline void *reallocarray(void *ptr, size_t nmemb, size_t size)
> > > >>                      ^
> > > >> /usr/include/stdlib.h:559:14: note: previous declaration is here
> > > >> extern void *reallocarray (void *__ptr, size_t __nmemb, size_t __size)
> > > >>               ^
> > > >> so perhaps the detection of
> > > >> COMPAT_NEED_REALLOCARRAY/feature-reallocarray is incorrect?
> > > >
> > > > Is this related to _DEFAULT_SOURCE vs _GNU_SOURCE.  via man 3 reallocarray:
> > > >         reallocarray():
> > > >             Since glibc 2.29:
> > > >                 _DEFAULT_SOURCE
> > > >             Glibc 2.28 and earlier:
> > > >                 _GNU_SOURCE
> > > >
> > >
> > > You can try the following patch to see whether it works or not.
> > >
> > > diff --git a/tools/build/feature/test-reallocarray.c
> > > b/tools/build/feature/test-reallocarray.c
> > > index 8f6743e31da7..500cdeca07a7 100644
> > > --- a/tools/build/feature/test-reallocarray.c
> > > +++ b/tools/build/feature/test-reallocarray.c
> > > @@ -1,5 +1,5 @@
> > >   // SPDX-License-Identifier: GPL-2.0
> > > -#define _GNU_SOURCE
> > > +#define _DEFAULT_SOURCE
> > >   #include <stdlib.h>
> > >
> > >   int main(void)
> > > @@ -7,4 +7,4 @@ int main(void)
> > >          return !!reallocarray(NULL, 1, 1);
> > >   }
> > >
> > > -#undef _GNU_SOURCE
> > > +#undef _DEFAULT_SOURCE
> >
> > Yeah, I had tried that. No luck though; same error message.  Even:
> >
> > $ cat foo.c
> > #define _DEFAULT_SOURCE
> > #include <stdlib.h>
> > void *reallocarray(void *ptr, size_t nmemb, size_t size) { return (void*)0; };
> > $ clang -c foo.c
> > $ echo $?
> > 0
> >
> > So I'm not sure precisely what's going on here.  I probably have to go
> > digging around to understand tools/build/feature/ anyways.  With your
> > v3 applied, I consistently see:
> > No zlib found
> > and yet, I certainly do have zlib on my host.
> > https://stackoverflow.com/a/54558861
> 
> Jiri, any tips on how to debug feature detection in
> tools/build/feature/Makefile?

for quick check, there's output file for each test, like:

	[jolsa@krava feature]$ ls -l *.make.output
	-rw-rw-r--. 1 jolsa jolsa   0 Apr  8 20:25 test-all.make.output
	-rw-rw-r--. 1 jolsa jolsa 182 Apr  9 15:52 test-bionic.make.output
	-rw-rw-r--. 1 jolsa jolsa   0 Apr  8 20:25 test-cplus-demangle.make.output
	-rw-rw-r--. 1 jolsa jolsa 145 Apr  9 15:52 test-jvmti.make.output
	-rw-rw-r--. 1 jolsa jolsa   0 Apr  8 20:25 test-libbabeltrace.make.output
	-rw-rw-r--. 1 jolsa jolsa   0 Apr  8 20:25 test-libbpf.make.output
	-rw-rw-r--. 1 jolsa jolsa   0 Apr  8 20:25 test-libdebuginfod.make.output
	-rw-rw-r--. 1 jolsa jolsa 193 Apr  9 15:52 test-libunwind-aarch64.make.output
	-rw-rw-r--. 1 jolsa jolsa 177 Apr  9 15:52 test-libunwind-x86.make.output
	[jolsa@krava feature]$ cat test-libunwind-aarch64.make.output
	test-libunwind-aarch64.c:2:10: fatal error: libunwind-aarch64.h: No such file or directory
	    2 | #include <libunwind-aarch64.h>
	      |          ^~~~~~~~~~~~~~~~~~~~~
	compilation terminated.
	[jolsa@krava feature]$ cat test-libunwind-x86.make.output
	test-libunwind-x86.c:2:10: fatal error: libunwind-x86.h: No such file or directory
	    2 | #include <libunwind-x86.h>
	      |          ^~~~~~~~~~~~~~~~~

zlib should be done by:
	[jolsa@krava feature]$ make test-zlib.bin
	gcc  -MD -Wall -Werror -o test-zlib.bin test-zlib.c  > test-zlib.make.output 2>&1 -lz


I can try to recreate, how do you build?

jirka