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

Peter Zijlstra
2021-07-01T08:37:43Z

On Wed, Jun 30, 2021 at 02:45:57PM +0200, Miroslav Benes wrote:
> > @@ -2725,15 +2820,24 @@ static int validate_branch(struct objtoo
> >
> > if (insn->visited & visited)
> > return 0;
> > - }
> > + } else
> > + nr_visited++;
>
> just a coding style
>
> } else {
> nr_visited++;
> }
>
> > @@ -3192,6 +3304,13 @@ int check(struct objtool_file *file)
> > warnings += ret;
> > }
> >
> > + if (stats) {
> > + printf("nr_visited: %ld\n", nr_visited);
>
> Could we make this nr_insns_visited?

Both done.

> > + printf("nr_cfi: %ld\n", nr_cfi);
> > + printf("nr_cfi_reused: %ld\n", nr_cfi_reused);
> > + printf("nr_cfi_cache: %ld\n", nr_cfi_cache);
> > + }
> > +
> > +++ 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.

> 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 :-)