Messages in this thread |  | | Date | Sat, 13 Jun 2020 12:49:12 -0700 | From | Matt Helsley <> | Subject | Re: [RFC][PATCH v4 18/32] objtool: mcount: Move nop_mcount() |
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On Fri, Jun 12, 2020 at 03:26:56PM +0200, Peter Zijlstra wrote: > On Tue, Jun 02, 2020 at 12:50:11PM -0700, Matt Helsley wrote: > > +static int nop_mcount(struct section * const rels, > > + const char *const txtname) > > +{ > > + struct reloc *reloc; > > + struct section *txts = find_section_by_index(lf, rels->sh.sh_info); > > + unsigned mcountsym = 0; > > + int once = 0; > > + > > + list_for_each_entry(reloc, &rels->reloc_list, list) { > > + int ret = -1; > > + > > + if (!mcountsym) > > + mcountsym = get_mcountsym(reloc); > > + > > + if (mcountsym == GELF_R_INFO(reloc->sym->idx, reloc->type) && !is_fake_mcount(reloc)) { > > This makes no sense to me; why not have mcountsym be a 'struct symbol > *' and have get_mcountsym() return one of those. > > if (reloc->sym == mcountsym && ... ) > > is much nicer, no?
Indeed! I'll change it from returning an unsigned long to struct symbol * before I move it out of the wrapper code.
> > > + if (make_nop) { > > + ret = make_nop(txts, reloc->offset); > > + if (ret < 0) > > + return -1; > > + } > > + if (warn_on_notrace_sect && !once) { > > + printf("Section %s has mcount callers being ignored\n", > > + txtname); > > + once = 1; > > + /* just warn? */ > > + if (!make_nop) > > + return 0; > > + } > > + } > > + > > + /* > > + * If we successfully removed the mcount, mark the relocation > > + * as a nop (don't do anything with it). > > + */ > > + if (!ret) { > > + reloc->type = rel_type_nop; > > + rels->changed = true; > > I have an elf_write_rela(), I'll make sure to Cc you.
Thanks! I might also make use of your patch to rewrite instructions. We need a way to turn certain prologue instructions into nops. Would it be more widely useful to move that functionality out of mcount and into the objtool ELF/per-arch code or do you think it's better inside the mcount subcommand code?
Cheers, -Matt
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