Re: [PATCH] ACPI: APEI: GHES: Disable KASAN instrumentation when compile testing with clang < 18

[Nathan Chancellor <nathan@kernel.org>]

On Tue, Jan 27, 2026 at 03:37:58PM +0100, Rafael J. Wysocki wrote:
> On Thu, Jan 15, 2026 at 12:27 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > After a recent innocuous change to drivers/acpi/apei/ghes.c, building
> > ARCH=arm64 allmodconfig with clang-17 or older (which has both
> > CONFIG_KASAN=y and CONFIG_WERROR=y) fails with:
> >
> >   drivers/acpi/apei/ghes.c:902:13: error: stack frame size (2768) exceeds limit (2048) in 'ghes_do_proc' [-Werror,-Wframe-larger-than]
> >     902 | static void ghes_do_proc(struct ghes *ghes,
> >         |             ^
> >
> > A KASAN pass that removes unneeded stack instrumentation, enabled by
> > default in clang-18 [1], drastically improves stack usage in this case.
> >
> > To avoid the warning in the common allmodconfig case when it can break
> > the build, disable KASAN for ghes.o when compile testing with clang-17
> > and older. Disabling KASAN outright may hide legitimate runtime issues,
> > so live with the warning in that case; the user can either increase the
> > frame warning limit or disable -Werror, which they should probably do
> > when debugging with KASAN anyways.
> >
> > Closes: https://github.com/ClangBuiltLinux/linux/issues/2148
> > Link: https://github.com/llvm/llvm-project/commit/51fbab134560ece663517bf1e8c2a30300d08f1a [1]
> > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> > ---
> >  drivers/acpi/apei/Makefile | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/acpi/apei/Makefile b/drivers/acpi/apei/Makefile
> > index 2c474e6477e1..346cdf0a0ef9 100644
> > --- a/drivers/acpi/apei/Makefile
> > +++ b/drivers/acpi/apei/Makefile
> > @@ -1,6 +1,10 @@
> >  # SPDX-License-Identifier: GPL-2.0
> >  obj-$(CONFIG_ACPI_APEI)                += apei.o
> >  obj-$(CONFIG_ACPI_APEI_GHES)   += ghes.o
> > +# clang versions prior to 18 may blow out the stack with KASAN
> > +ifeq ($(CONFIG_COMPILE_TEST)_$(CONFIG_CC_IS_CLANG)_$(call clang-min-version, 180000),y_y_)
> > +KASAN_SANITIZE_ghes.o := n
> > +endif
> >  obj-$(CONFIG_ACPI_APEI_EINJ)   += einj.o
> >  einj-y                         := einj-core.o
> >  einj-$(CONFIG_ACPI_APEI_EINJ_CXL) += einj-cxl.o
> >
> > ---
> 
> I'm inclined to apply this for 6.20/7.0 unless someone has any
> particular heartburn related to it.

I think taking it for next cycle is fine, I can just apply this to our
CI until it makes its way to Linus. Could you stick a

  Cc: stable@vger.kernel.org

on the patch in that case so that it can go back to 6.18 after the
initial flurry of the merge window?

Cheers,
Nathan