On Wed, 5 Mar 2025 at 00:21, Kees Cook <k...@kernel.org> wrote:
>
> The UM builds distinguish i386 from x86_64 via SUBARCH, but we don't
> support building i386 directly with Clang. To make SUBARCH work for
> i386 UM, we need to explicitly test for it.
>
> This lets me run i386 KUnit tests with Clang:
>
> $ ./tools/testing/kunit/kunit.py run \
> --make_options LLVM=1 \
> --make_options SUBARCH=i386
> ...
>
> Fixes: c7500c1b53bf ("um: Allow builds with Clang")
> Signed-off-by: Kees Cook <k...@kernel.org>
> ---Thanks for this -- I'd been using `--kconfig_add CONFIG_64BIT=n` as a way to build i386 UML kernels, which seems to work even without this patch -- but this is definitely an improvement. It may be worth noting that CONFIG_FORTIFY_SOURCE is incompatible with clang + i386, which seems to affect UML as well. (That might actually not be required, as I think UML doesn't use any of the strange -mregparm calling convention stuff which appears to be what breaks FORTIFY_SOURCE here.) Regardless, Tested-by: David Gow <david...@google.com> Cheers, -- David > Cc: Nathan Chancellor <nat...@kernel.org> > Cc: Thomas Weißschuh <li...@weissschuh.net> > Cc: Bill Wendling <mo...@google.com> > Cc: Justin Stitt <justinst...@google.com> > Cc: Masahiro Yamada <masahi...@kernel.org> > Cc: Nicolas Schier <nico...@fjasle.eu> > Cc: l...@lists.linux.dev > Cc: linux-kbu...@vger.kernel.org > --- > scripts/Makefile.clang | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang > index 2435efae67f5..b67636b28c35 100644 > --- a/scripts/Makefile.clang > +++ b/scripts/Makefile.clang > @@ -12,6 +12,8 @@ CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu > CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu > CLANG_TARGET_FLAGS_sparc := sparc64-linux-gnu > CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu > +# This is only for i386 UM builds, which need the 32-bit target not -m32 > +CLANG_TARGET_FLAGS_i386 := i386-linux-gnu > CLANG_TARGET_FLAGS_um := $(CLANG_TARGET_FLAGS_$(SUBARCH)) > CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH)) > > -- > 2.34.1 >
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