linux-kernel - Re: [PATCH v2 9/9] objtool: Abstract unwind hint reading

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Date:   Fri, 31 Jul 2020 09:04:41 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Julien Thierry <jthierry@...hat.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org, mbenes@...e.cz,
        raphael.gault@....com, benh@...nel.crashing.org
Subject: Re: [PATCH v2 9/9] objtool: Abstract unwind hint reading

On Fri, Jul 31, 2020 at 08:00:58AM +0100, Julien Thierry wrote:
> > > +	cfa->offset = hint->sp_offset;
> > > +	insn->cfi.hint_type = hint->type;
> > > +	insn->cfi.end = hint->end;
> > > +
> > > +	insn->cfi.sp_only = hint->type == ORC_TYPE_REGS || hint->type == ORC_TYPE_REGS_IRET;
> > 
> > What does "sp" mean here in sp_only?
> > 
> 
> Stack pointer, like in CFI_SP. When objtool encounters one of these hints,
> it starts to only track the stack frame with the stack pointer (no BP, no
> drap register, no move to temporary registers). Just trying to make some
> sense of this corner case.

I think that's not quite right, because ORC_TYPE_CALL could also be
"sp_only" in some cases, by that definition.

The call to update_cfi_state_regs() is really regs-specific, not
sp-specific.

-- 
Josh