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

[Brian Gerst]

On Fri, Dec 6, 2024 at 9:37 AM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> 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>

Using PROVIDES() is now unnecessary.


Brian Gerst