Re: [RFC PATCH 4/4] objtool/powerpc: Add --mcount specific implementation

[Naveen N. Rao]

Christophe Leroy wrote:
> Le 25/05/2022 à 19:27, Christophe Leroy a écrit :
> > Le 24/05/2022 à 15:33, Christophe Leroy a écrit :
> > > Le 24/05/2022 à 13:00, Sathvika Vasireddy a écrit :
> > > > > > +{
> > > > > > +    switch (elf->ehdr.e_machine) {
> > > > > > +    case EM_X86_64:
> > > > > > +            return R_X86_64_64;
> > > > > > +    case EM_PPC64:
> > > > > > +            return R_PPC64_ADDR64;
> > > > > > +    default:
> > > > > > +            WARN("unknown machine...");
> > > > > > +            exit(-1);
> > > > > > +    }
> > > > > > +}
> > > > > Wouldn't it be better to make that function arch specific ?
> > > >
> > > > This is so that we can support cross architecture builds.
> > >
> > >
> > > I'm not sure I follow you here.
> > >
> > > This is only based on the target, it doesn't depend on the build host so
> > > I can't the link with cross arch builds.
> > >
> > > The same as you have arch_decode_instruction(), you could have
> > > arch_elf_reloc_type_long()
> > > It would make sense indeed, because there is no point in supporting X86
> > > relocation when you don't support X86 instruction decoding.
> >
> > Could simply be some macro defined in 
> > tools/objtool/arch/powerpc/include/arch/elf.h and 
> > tools/objtool/arch/x86/include/arch/elf.h
> >
> > The x86 version would be:
> >
> > #define R_ADDR(elf) R_X86_64_64
> >
> > And the powerpc version would be:
> >
> > #define R_ADDR(elf) (elf->ehdr.e_machine == EM_PPC64 ? R_PPC64_ADDR64 : 
> > R_PPC_ADDR32)
>
> Well, looking once more, and taking into account the patch from Chen 
> https://lore.kernel.org/lkml/20220531020744.236970-4-chenzhongjin@xxxxxxxxxx/
>
> It would be easier to just define two macros:
>
> #define R_ABS64 R_PPC64_ADDR64
> #define R_ABS32 R_PPC_ADDR32
>
> And then in the caller, as we know the size, do something like
>
> 	size == sizeof(u64) ? R_ABS64 : R_ABS32;

How does 'sizeof(u64)' work here?


- Naveen