bug#79491: coreutils build failure with -mno-pclmul

On 22/09/2025 19:39, Sam James wrote:
> Hi,
> 
> We had a report downstream in Gentoo at https://bugs.gentoo.org/959467
> of a build failure for coreutils when pasisng -mno-pclmul.
> 
> Ionen's analysis on the bug seems good to me, so quoting that:
> """
> Haven't looked all that in-depth, but I wonder why src/cksum.c checks for gnulib's GL_CRC_X86_64_PCLMUL at all, and also why it manages to be set?

cksum.c checks GL_CRC_X86_64_PCLMUL only so it prints appropriate --debug info.
You could remove the "|| GL_CRC_X86_64_PCLMUL" clause and just loose that minor
feature with `cksum -a crc32b`
> coreutils own's pclmul check to set USE_PCLMUL_CRC32 does:
> 
>      ac_save_CFLAGS=$CFLAGS
>      CFLAGS="-mavx -mpclmul $CFLAGS"
> 
> CFLAGS here has -mno-pclmul and comes after -mpclmul, so as expected:
> 
>      checking if vmull intrinsic exists... no
>      checking if pclmul intrinsic exists... no
>      checking if avx2 pclmul intrinsic exists... no
>      checking if avx512 pclmul intrinsic exists... no
> 
> But then there is another (lone) check, done by gnulib's m4/crc-x86_64.m4 which pass for some reason (despite i686 and -mno-pclmul) and sets GL_CRC_X86_64_PCLMUL:
> 
>      checking if pclmul intrinsic exists... yes

Well that should be fixed anyway.

> 
> Then pclmul_supported function has:
> 
>      # if USE_PCLMUL_CRC32 || GL_CRC_X86_64_PCLMUL
> 
> And finally src/cksum_pclmul.c is only built if USE_PCLMUL_CRC32, while GL_CRC_X86_64_PCLMUL builds lib/crc-x86_64-pclmul.c (I see it in the build.log)
> 
> However crc-x86_64-pclmul.c does not define cksum_pclmul, and
> pclmul_supported does not use anything from that crc-x86_64-pclmul.c
> that I can see? I could be missing something but the simple fix may be
> to just drop the "|| GL_CRC_X86_64_PCLMUL" check.
> """
> 
> I can reproduce it with e.g. coreutils-9.8 with:

I think you would have seen the same with coreutils-9.7
> $ ./configure CFLAGS="-march=westmere -mno-aes -mno-avx -mno-pclmul -O2 -pipe"
> $ make
> /usr/lib/gcc/x86_64-pc-linux-gnu/16/../../../../x86_64-pc-linux-gnu/bin/ld: src/cksum-cksum.o: in function `pclmul_supported':
> cksum.c:(.text+0x2c6): undefined reference to `cksum_pclmul'
> collect2: error: ld returned 1 exit status
> make[2]: *** [Makefile:11791: src/cksum] Error 1
Note the gl_cv_crc_pclmul and utils_cv_pclmul_intrinsic_exists configure vars
are higher level ways to configure this feature in the coreutils build.

cheers,
Padraig