Re: [PATCH] vmlinux.lds.h: Handle clang's module.{c,d}tor sections

[Nathan Chancellor]

On 7/30/2021 3:59 PM, Fangrui Song wrote:
> On 2021-07-30, Nick Desaulniers wrote:
> > On Fri, Jul 30, 2021 at 3:38 PM Nathan Chancellor <nathan@xxxxxxxxxx> 
> > wrote:
> > > A recent change in LLVM causes module_{c,d}tor sections to appear when
> > > CONFIG_K{A,C}SAN are enabled, which results in orphan section warnings
> > > because these are not handled anywhere:
> > >
> > > ld.lld: warning: 
> > > arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_ctor) is being 
> > > placed in '.text.asan.module_ctor'
> > > ld.lld: warning: 
> > > arch/x86/pci/built-in.a(legacy.o):(.text.asan.module_dtor) is being 
> > > placed in '.text.asan.module_dtor'
> > > ld.lld: warning: 
> > > arch/x86/pci/built-in.a(legacy.o):(.text.tsan.module_ctor) is being 
> > > placed in '.text.tsan.module_ctor'
> >
> > ^ .text.tsan.*
>
> I was wondering why the orphan section warning only arose recently.
> Now I see: the function asan.module_ctor has the SHF_GNU_RETAIN flag, so
> it is in a separate section even with -fno-function-sections (default).

Thanks for the explanation, I will add this to the commit message.

> It seems that with -ffunction-sections the issue should have been caught
> much earlier.
>
> > > Place them in the TEXT_TEXT section so that these technologies continue
> > > to work with the newer compiler versions. All of the KASAN and KCSAN
> > > KUnit tests continue to pass after this change.
> > >
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/1432
> > > Link: 
> > > https://github.com/llvm/llvm-project/commit/7b789562244ee941b7bf2cefeb3fc08a59a01865 
> > >
> > > Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> > > ---
> > >  include/asm-generic/vmlinux.lds.h | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/include/asm-generic/vmlinux.lds.h 
> > > b/include/asm-generic/vmlinux.lds.h
> > > index 17325416e2de..3b79b1e76556 100644
> > > --- a/include/asm-generic/vmlinux.lds.h
> > > +++ b/include/asm-generic/vmlinux.lds.h
> > > @@ -586,6 +586,7 @@
> > >                 
> > > NOINSTR_TEXT                                            \
> > >                 
> > > *(.text..refcount)                                      \
> > >                 
> > > *(.ref.text)                                            \
> > > +               *(.text.asan 
> > > .text.asan.*)                              \
> >
> > Will this match .text.tsan.module_ctor?

No, I forgot to test CONFIG_KCSAN with this version, rather than the 
prior one I had on GitHub so I will send v2 shortly.

> asan.module_ctor is the only function AddressSanitizer synthesizes in 
> the instrumented translation unit.
> There is no function called "asan".
>
> (Even if a function "asan" exists due to -ffunction-sections
> -funique-section-names, TEXT_MAIN will match .text.asan, so the
> .text.asan pattern will match nothing.)

Sounds good, I will update it to remove the .text.asan and replace it 
with .text.tsan.*

> > Do we want to add these conditionally on
> > CONFIG_KASAN_GENERIC/CONFIG_KCSAN like we do for SANITIZER_DISCARDS?

I do not think there is a point in doing so but I can if others feel 
strongly.

Thank you both for the comments for the comments!

Cheers,
Nathan