Re: [PATCH] x86/stackprotector: fix build failure with CONFIG_STACKPROTECTOR=n

[Ard Biesheuvel]

On Fri, 6 Dec 2024 at 15:22, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> On 12/06, Ard Biesheuvel wrote:
> >
> > On Fri, 6 Dec 2024 at 13:32, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> > >
> > > +#ifdef CONFIG_STACKPROTECTOR
> > >  /* needed for Clang - see arch/x86/entry/entry.S */
> > >  PROVIDE(__ref_stack_chk_guard = __stack_chk_guard);
> > > +#endif
> > >
> > >  #ifdef CONFIG_X86_64
> > >  /*
> >
> > This shouldn't be necessary - PROVIDE() is only evaluated if a
> > reference exists to the symbol it defines.
> >
> > Also, I'm failing to reproduce this. Could you share your .config,
> > please, and the error that you get during the build?
>
> Please see the attached .config
>
> without the change above:
>
>         $ make bzImage
>           CALL    scripts/checksyscalls.sh
>           DESCEND objtool
>           INSTALL libsubcmd_headers
>           UPD     include/generated/utsversion.h
>           CC      init/version-timestamp.o
>           KSYMS   .tmp_vmlinux0.kallsyms.S
>           AS      .tmp_vmlinux0.kallsyms.o
>           LD      .tmp_vmlinux1
>         ./arch/x86/kernel/vmlinux.lds:154: undefined symbol `__stack_chk_guard' referenced in expression
>         scripts/Makefile.vmlinux:77: recipe for target 'vmlinux' failed
>         make[2]: *** [vmlinux] Error 1
>         /home/oleg/tmp/LINUX/Makefile:1225: recipe for target 'vmlinux' failed
>         make[1]: *** [vmlinux] Error 2
>         Makefile:251: recipe for target '__sub-make' failed
>         make: *** [__sub-make] Error 2
>
> perhaps this is because my toolchain is quite old,
>
>         $ ld -v
>         GNU ld version 2.25-17.fc23
>
> but according to Documentation/process/changes.rst
>
>         binutils               2.25             ld -v
>
> it is still supported.
>

We're about to bump the minimum toolchain requirements to GCC 8.1 (and
whichever version of binutils was current at the time), so you might
want to consider upgrading.

However, you are right that these are still supported today, and so we
need this fix this, especially because this has been backported to
older stable kernels too.

For the patch,

Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>