Re: [PATCH] arm64: disable -fsanitize=shadow-call-stack for big-endian

[Fangrui Song]

On 2020-05-27, Arnd Bergmann wrote:
> On Wed, May 27, 2020 at 7:28 PM 'Nick Desaulniers' via Clang Built
> Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
> > On Wed, May 27, 2020 at 8:24 AM Mark Rutland <mark.rutland@xxxxxxx> wrote:
> > >
> > > On Wed, May 27, 2020 at 03:39:46PM +0200, Arnd Bergmann wrote:
> > > > clang-11 and earlier do not support -fsanitize=shadow-call-stack
> > > > in combination with -mbig-endian, but the Kconfig check does not
> > > > pass the endianess flag, so building a big-endian kernel with
> > > > this fails at build time:
> > > >
> > > > clang: error: unsupported option '-fsanitize=shadow-call-stack' for target 'aarch64_be-unknown-linux'
> > > >
> > > > Change the Kconfig check to let Kconfig figure this out earlier
> > > > and prevent the broken configuration. I assume this is a bug
> > > > in clang that needs to be fixed, but we also have to work
> > > > around existing releases.
> > > >
> > > > Fixes: 5287569a790d ("arm64: Implement Shadow Call Stack")
> > > > Link: https://bugs.llvm.org/show_bug.cgi?id=46076
> > > > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > >
> > > I suspect this is similar to the patchable-function-entry issue, and
> > > this is an oversight that we'd rather fix toolchain side.
> > >
> > > Nick, Fangrui, thoughts?
> >
> > Exactly, Fangrui already has a fix: https://reviews.llvm.org/D80647.
> > Thanks Fangrui!
>
> Ok, great! I had opened the bug first so I could reference it in the
> commit changelog, it seems the fix came fast than I managed to
> send out the kernel workaround.
>
> Do we still want the kernel workaround anyway to make it work
> with older clang versions, or do we expect to fall back to not
> use the integrated assembler for the moment?
>
>      Arnd

We can condition it on `CLANG_VERSION >= 100001` (assuming Tom (CCed)
is happy (and there is still time) cherrying pick the two commits https://bugs.llvm.org/show_bug.cgi?id=46076 to clang 10.0.1)