Re: [PATCH 3/5] objtool: Support Clang non-section symbols in ORC generation

Josh Poimboeuf
2020-04-01T19:05:58Z

On Wed, Apr 01, 2020 at 08:49:53PM +0200, Peter Zijlstra wrote:
> On Wed, Apr 01, 2020 at 01:23:27PM -0500, Josh Poimboeuf wrote:
>
> > @@ -105,8 +100,32 @@ static int create_orc_entry(struct elf *elf, struct section *u_sec, struct secti
> > }
> > memset(rela, 0, sizeof(*rela));
> >
> > - rela->sym = insn_sec->sym;
> > - rela->addend = insn_off;
> > + if (insn_sec->sym) {
> > + rela->sym = insn_sec->sym;
> > + rela->addend = insn_off;
> > + } else {
> > + /*
> > + * The Clang assembler doesn't produce section symbols, so we
> > + * have to reference the function symbol instead:
> > + */
> > + rela->sym = find_symbol_containing(insn_sec, insn_off);
>
> It's a good thing I made that a lot faster I suppose ;-)

:-)

> > + if (!rela->sym) {
> > + /*
> > + * Hack alert. This happens when we need to reference
> > + * the NOP pad insn immediately after the function.
> > + */
> > + rela->sym = find_symbol_containing(insn_sec,
> > + insn_off - 1);
>
> Urgh, when does that happen?

It happens naturally in the padding between functions, since objtool
doesn't traverse those instructions. So they have undefined entries
like

.text+68: sp:(und) bp:(und) type:call end:0

I suppose those aren't technically necessary.

--
Josh