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

[Yonghong Song <yhs@fb.com>]

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
[yhs@devbig003.ftw2 ~/work/bpf-next/tools/build]$

> $ cd tools/testing/selftests/bpf
> $ grep -rn _DEFAULT_SOURCE | wc -l
> 0
> $ grep -rn _GNU_SOURCE | wc -l
> 37
> $ ldd --version | head -n1
> ldd (Debian GLIBC 2.31-9+build1) 2.31
>