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
