Re: [PATCH] printf: mark errptr() noinline

[Tamir Duberstein]

On Sun, Apr 5, 2026 at 1:32 PM Tamir Duberstein <tamird@xxxxxxxxxx> wrote:
>
> Old GCC can miscompile printf_kunit's errptr() test when branch
> profiling is enabled. BUILD_BUG_ON(IS_ERR(PTR)) is a constant false
> expression, but CONFIG_TRACE_BRANCH_PROFILING and
> CONFIG_PROFILE_ALL_BRANCHES make the IS_ERR() path side-effectful.
> GCC's IPA splitter can then outline the cold assert arm into
> errptr.part.* and leave that clone with an unconditional
> __compiletime_assert_*() call, causing a false build failure.
>
> This started showing up after test_hashed() became a macro and moved its
> local buffer into errptr(), which changed GCC's inlining and splitting
> decisions enough to expose the compiler bug.
>
> Mark errptr() noinline to keep it out of that buggy IPA path while
> preserving the BUILD_BUG_ON(IS_ERR(PTR)) check and the macro-based
> printf argument checking.
>
> Fixes: 9bfa52dac27a ("printf: convert test_hashed into macro")
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-kbuild-all/202604030636.NqjaJvYp-lkp@xxxxxxxxx/
> Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxxx>

Adding tag per stable instructions:

Cc: stable@xxxxxxxxxxxxxxx