Re: [PATCH v4 04/10] objtool: Handle PC relative relocation type

[Tiezhu Yang]

On 11/26/2024 07:00 PM, Tiezhu Yang wrote:
> On 11/26/2024 03:19 PM, Josh Poimboeuf wrote:
> > On Fri, Nov 22, 2024 at 12:49:59PM +0800, Tiezhu Yang wrote:
> > > When compling with Clang on LoongArch, there exists 32 bit PC relative
> > > relocation type, it needs to get the offset with "S + A - PC" according
> > > to the spec of "ELF for the LoongArch Architecture".
> > >
> > > This is preparation for later patch on LoongArch, there is no effect for
> > > the other archs with this patch.
> > >
> > > Link: https://github.com/loongson/la-abi-specs/blob/release/laelf.adoc
> > > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> > > ---
> > >  tools/objtool/check.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> > > index 19d1263e64e4..8733ca620cca 100644
> > > --- a/tools/objtool/check.c
> > > +++ b/tools/objtool/check.c
> > > @@ -2126,6 +2126,11 @@ static int add_jump_table(struct objtool_file
> > > *file, struct instruction *insn,
> > >          if (reloc->sym->type == STT_SECTION) {
> > >              /* Addend field in the relocation entry associated with
> > > the symbol */
> > >              offset = reloc_addend(reloc);
> > > +            /* Handle the special cases compiled with Clang on
> > > LoongArch */
> > > +            if (file->elf->ehdr.e_machine == EM_LOONGARCH &&
> > > +                reloc_type(reloc) == R_LARCH_32_PCREL)
> > > +                offset = reloc->sym->offset + reloc_addend(reloc) -
> > > +                     (reloc_offset(reloc) - reloc_offset(table));
> >
> > Please, no more "special cases".  It makes the common code unreadable.
> > We should avoid checking 'elf->ehdr.e_machine' in check.c.
>
> OK.
>
> > Maybe there should be an arch-specific function arch_adjusted_addend().

Add adjust_offset() in
tools/objtool/include/objtool/elf.h,
like this:

static inline unsigned long adjust_offset(struct elf *elf, struct reloc 
*reloc,
                                          unsigned long offset)
{
        if (elf->ehdr.e_machine == EM_LOONGARCH && reloc_type(reloc) == 
R_LARCH_32_PCREL)
                offset = reloc->sym->offset + reloc_addend(reloc) -
                         (reloc_offset(reloc) - reloc_offset(table));

        return offset;
}

then call it in check.c, like this:

offset = reloc->sym->offset + reloc_addend(reloc);
offset = adjust_offset(file->elf, reloc, offset);

What do you think?

Thanks,
Tiezhu