Re: [PATCH v3 04/12] module: Add printk format to add module build ID to stacktraces

Stephen Boyd
2021-04-08T19:57:19Z

Quoting Andy Shevchenko (2021-04-08 07:05:54)
> On Thu, Apr 08, 2021 at 03:44:57PM +0200, Jessica Yu wrote:
> > +++ Stephen Boyd [30/03/21 20:05 -0700]:
>
> ...
>
> > > +static void init_build_id(struct module *mod, const struct load_info *info)
> > > +{
> > > + const Elf_Shdr *sechdr;
> > > + unsigned int i;
> > > +
> > > + for (i = 0; i < info->hdr->e_shnum; i++) {
> > > + sechdr = &info->sechdrs[i];
> > > + if (!sect_empty(sechdr) && sechdr->sh_type == SHT_NOTE &&
> > > + !build_id_parse_buf((void *)sechdr->sh_addr, mod->build_id,
> > > + sechdr->sh_size))
> > > + break;
> > > + }
> > > +}
> >
> > Why not just look for the .note.gnu.build-id section instead of trying
> > to parse each note section? Doesn't it always contain the build id? At
> > least the ld man page seems to suggest this section name should be
> > consistent.

That's basically what this code is doing. We're looking through all the
section headers and finding the ones that are notes and then
build_id_parse_buf() is checking to see if that note is a GNU type note
(name == "GNU") and is of the type NT_GNU_BUILD_ID (type == 3). We don't
need to check for a section name of ".note.gnu.build-id", we can use the
existing code in build_id_parse_buf() that looks for the name and type.

>
> Interesting idea (in positive way!), I'm wondering what Clang does in such
> case.
>

Clang also inserts a GNU build ID and it works with these patches.