Re: [akpm-mm:mm-unstable 121/130] tools/testing/selftests/kselftest.h:427:13: error: implicit declaration of function 'vasprintf'; did you mean 'vsprintf'?

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 31 Mar 2026 11:27:20 +0200 kernel test robot <lkp@intel.com> wrote:

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable
> head:   24e341657c283c965e3bfee0baa9ed0376127973
> commit: cc0b04b10a7b98fd8df2fd539177e94e0f83a5c3 [121/130] selftests: ksft_exit_fail_perror: support printf style arguments
> config: arm64-allnoconfig-bpf (https://download.01.org/0day-ci/archive/20260331/202603311105.ysUeYPSZ-lkp@intel.com/config)
> compiler: aarch64-linux-gnu-gcc (Debian 14.2.0-19) 14.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260331/202603311105.ysUeYPSZ-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202603311105.ysUeYPSZ-lkp@intel.com/
> 
> Note: the akpm-mm/mm-unstable HEAD 24e341657c283c965e3bfee0baa9ed0376127973 builds fine.
>       It only hurts bisectability.
> 
> All errors (new ones prefixed by >>):
> 
>    In file included from za-fork.c:12:
>    ../../kselftest.h: In function 'ksft_exit_fail_perror':
> >> ../../kselftest.h:427:13: error: implicit declaration of function 'vasprintf'; did you mean 'vsprintf'? [-Wimplicit-function-declaration]
>      427 |         if (vasprintf(&buf, msg, args) == -1) {
>          |             ^~~~~~~~~
>          |             vsprintf

What's going on here.  vasprintf is a GNU thing, but that isn't it. 
kselftest.h includes stdio.h directly so fine.  I don't see anything in
the later patches which could alter this, so the "only hurts
bisectability" is inexplicable.

I was able to reproduce this, once.  Now it's gone away.


And arm64 allnoconfig is a nuisance.  Now my vmlinux build immediately
faceplants with

./arch/arm64/include/asm/atomic_ll_sc.h:298:9: error: unknown type name 'u128'
  298 |         u128 full;

With the latest 15.2.0 kit from https://www.kernel.org/pub/tools/crosstool/.