Bug 1650072

Mark, does this mean that supporting those compressed elf objects from rpm a matter of essentially:

--- a/build/files.c
+++ b/build/files.c
@@ -1804,7 +1804,7 @@ static int generateBuildIDs(FileList fl, ARGV_t *files)
                   kernel modules (ET_REL files with names ending in .ko)
                   should have build-ids. */
                GElf_Ehdr ehdr;
-               Elf *elf = elf_begin (fd, ELF_C_READ, NULL);
+               Elf *elf = dwelf_elf_begin (fd);
                if (elf != NULL && elf_kind(elf) == ELF_K_ELF
                    && gelf_getehdr(elf, &ehdr) != NULL
                    && (ehdr.e_type == ET_EXEC || ehdr.e_type == ET_DYN

...or is it more something considerably more involved?

(In reply to Panu Matilainen from comment #1)
> Mark, does this mean that supporting those compressed elf objects from rpm a
> matter of essentially:
> 
> --- a/build/files.c
> +++ b/build/files.c
> @@ -1804,7 +1804,7 @@ static int generateBuildIDs(FileList fl, ARGV_t *files)
>                    kernel modules (ET_REL files with names ending in .ko)
>                    should have build-ids. */
>                 GElf_Ehdr ehdr;
> -               Elf *elf = elf_begin (fd, ELF_C_READ, NULL);
> +               Elf *elf = dwelf_elf_begin (fd);
>                 if (elf != NULL && elf_kind(elf) == ELF_K_ELF
>                     && gelf_getehdr(elf, &ehdr) != NULL
>                     && (ehdr.e_type == ET_EXEC || ehdr.e_type == ET_DYN
> 
> ...or is it more something considerably more involved?

Basically, yes for the build-id handling. It obviously needs some testing. Some configure magic, to make sure you have elfutils 0.175 (libdw with dwelf_elf_begin).

There is the interaction with find-debuginfo.sh/debugedit (which don't handle compressed ELF files at the moment). So that you also can extract debuginfo from compressed ELF files (currently the kernel.spec works around this with a trick to call find-debuginfo.sh before compressing, which is a bit of a hack). Technically a separate issue, bug obviously related.

Created attachment 1528946 [details]
Support build-id generation from compressed ELF files on elfutils >= 0.175

So something like this? 

Tested to the point that it compiles with elfutils 0.174 and 0.175 and test-suite passes when dwelf_elf_begin() is used. Not too keen to test an actual kernel build on this poor old laptop :)

(In reply to Panu Matilainen from comment #3)
> Created attachment 1528946 [details]
> Support build-id generation from compressed ELF files on elfutils >= 0.175
> 
> So something like this? 

Yes, but note the code has this hacky test:

                /* Only real ELF files, that are ET_EXEC, ET_DYN or
                   kernel modules (ET_REL files with names ending in .ko)
                   should have build-ids. */

[...]
                        || (ehdr.e_type == ET_REL
                            && rpmFileHasSuffix (flp->diskPath, ".ko"))

So we also need to change the detection of whether a file is a kernel module.
(Note that we cannot just pick any ET_REL file, because those are normally
object files that still need linking, and won't have a build-id.)

Since kernel modules can be compressed with various variants (.gz, .bz2, .xz) we either recognize them all as .ko.xx or we do something smarter like looking if there is a .modinfo section and we can parse it (like modinfo does).

A more complete version with .modinfo detection submitted upstream now: 
https://github.com/rpm-software-management/rpm/pull/653

Mark, I'd appreciate if you could take review the patch(es):
https://github.com/rpm-software-management/rpm/pull/653

(In reply to Panu Matilainen from comment #6)
> Mark, I'd appreciate if you could take review the patch(es):
> https://github.com/rpm-software-management/rpm/pull/653

I reviewed the patches on rpm-maint. Look good to me. Thanks.

This is supposedly fixed in rpm-4.14.2.1-10.fc31 now. Please verify.

[pmatilai🎩︎sopuli Downloads]$ rpm -qplv kernel-debuginfo-5.2.0-0.rc3.git0.1.fc31.x86_64.rpm|grep build-id|grep /modules/|head -5
lrwxrwxrwx    1 root     root                      103 Jun  3 16:59 /usr/lib/debug/.build-id/00/20b13ba1b9a1844cf5be28b77692f21bfbce0b -> ../../../../../lib/modules/5.2.0-0.rc3.git0.1.fc31.x86_64/kernel/net/netfilter/ipset/ip_set_hash_mac.ko
lrwxrwxrwx    1 root     root                      123 Jun  3 16:59 /usr/lib/debug/.build-id/00/20b13ba1b9a1844cf5be28b77692f21bfbce0b.debug -> ../../../../../usr/lib/debug/lib/modules/5.2.0-0.rc3.git0.1.fc31.x86_64/kernel/net/netfilter/ipset/ip_set_hash_mac.ko.debug
lrwxrwxrwx    1 root     root                       84 Jun  3 16:59 /usr/lib/debug/.build-id/00/35fe5e6106599c4298683378f932577e28ccad -> ../../../../../lib/modules/5.2.0-0.rc3.git0.1.fc31.x86_64/extra/net/netrom/netrom.ko
lrwxrwxrwx    1 root     root                      104 Jun  3 16:59 /usr/lib/debug/.build-id/00/35fe5e6106599c4298683378f932577e28ccad.debug -> ../../../../../usr/lib/debug/lib/modules/5.2.0-0.rc3.git0.1.fc31.x86_64/extra/net/netrom/netrom.ko.debug
lrwxrwxrwx    1 root     root                       93 Jun  3 16:59 /usr/lib/debug/.build-id/00/60beca4a039e5d9d11aa1f76aa4e232c1cdcb6 -> ../../../../../lib/modules/5.2.0-0.rc3.git0.1.fc31.x86_64/kernel/drivers/gpio/gpio-amd-fch.ko


Also comparing the number of build-ids against an older build prior to the fix shows a big increase:

[pmatilai🎩︎sopuli Downloads]$ rpm -qplv kernel-debuginfo-5.2.0-0.rc3.git0.1.fc31.x86_64.rpm | grep build-id|wc -l
7158
[pmatilai🎩︎sopuli Downloads]$ rpm -qplv kernel-debuginfo-5.2.0-0.rc1.git0.1.fc31.x86_64.rpm |grep build-id|wc -l
57

AFAICS this is working as expected then.

The needinfo request[s] on this closed bug have been removed as they have been unresolved for 1000 days