linux-kernel - Re: [PATCH v2 02/24] objtool: Introduce CFI hash

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Date:   Thu, 1 Jul 2021 10:53:52 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     jpoimboe@...hat.com, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, joro@...tes.org,
        boris.ostrovsky@...cle.com, jgross@...e.com, x86@...nel.org,
        mbenes@...e.com, rostedt@...dmis.org, dvyukov@...gle.com,
        elver@...gle.com, Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH v2 02/24] objtool: Introduce CFI hash

> > > +++ b/tools/objtool/orc_gen.c
> > > @@ -13,13 +13,19 @@
> > >  #include <objtool/warn.h>
> > >  #include <objtool/endianness.h>
> > >  
> > > -static int init_orc_entry(struct orc_entry *orc, struct cfi_state *cfi)
> > > +static int init_orc_entry(struct orc_entry *orc, struct cfi_state *cfi,
> > > +			  struct instruction *insn)
> > >  {
> > > -	struct instruction *insn = container_of(cfi, struct instruction, cfi);
> > >  	struct cfi_reg *bp = &cfi->regs[CFI_BP];
> > >  
> > >  	memset(orc, 0, sizeof(*orc));
> > >  
> > > +	if (!cfi) {
> > > +		orc->end = 0;
> > > +		orc->sp_reg = ORC_REG_UNDEFINED;
> > > +		return 0;
> > > +	}
> > > +
> > 
> > This looks strange. You access cfi a couple of lines earlier (bp cfi_reg 
> > initialization).
> 
> That's a relative address compute, it doesn't actually dereference the
> pointer.

Right, I misread the line.
 
> > Is it even possible to have cfi == NULL here? The second call site below 
> > has a check and the first one should not happen (insn->cfip should be 
> > always set if I am not missing something).
> 
> I can happen for instructions that are not visited, like NOP fillers
> between functions. Remove the check and try to build a file :-)

Doh, I should have done that. Of course there must be unvisited 
instructions. Sorry for the noise.

Miroslav