Re: [PATCH v3 03/12] dump_stack: Add vmlinux build ID to stack traces

Petr Mladek
2021-04-08T10:13:27Z

On Wed 2021-04-07 23:20:32, Stephen Boyd wrote:
> Quoting Petr Mladek (2021-04-07 07:03:19)
> > # readelf -Wn vmlinux-5.12.0-rc6-default+
> >
> > Displaying notes found in: .notes
> > Owner Data size Description
> > Xen 0x00000006 Unknown note type: (0x00000006) description data: 6c 69 6e 75 78 00
> > Xen 0x00000004 Unknown note type: (0x00000007) description data: 32 2e 36 00
> > Xen 0x00000008 Unknown note type: (0x00000005) description data: 78 65 6e 2d 33 2e 30 00
> > Xen 0x00000008 Unknown note type: (0x00000003) description data: 00 00 00 ffffff80 ffffffff ffffffff ffffffff ffffffff
> >
>
> Thanks for the readelf output. That was most helpful to see what's going
> on. The buildid code isn't prepared for this it seems. We'll need to
> check the note data to see if it starts with "GNU\0" and if it does then
> we use it as the buildid. I'm not sure what this Xen note is that has a
> type of 3 but I think that's OK, it won't have "GNU" in there so we
> should ignore it. Does this patch work?
>
> ----8<----
> diff --git a/lib/buildid.c b/lib/buildid.c
> index 483abf71eeec..f281dbe6fb83 100644
> --- a/lib/buildid.c
> +++ b/lib/buildid.c
> @@ -25,6 +25,7 @@ static int parse_build_id_buf(unsigned char *build_id,
>
> if (nhdr->n_type == BUILD_ID &&
> nhdr->n_namesz == sizeof("GNU") &&
> + !strcmp((char *)(nhdr + 1), "GNU") &&
> nhdr->n_descsz > 0 &&
> nhdr->n_descsz <= BUILD_ID_SIZE_MAX) {
> memcpy(build_id,

It helped with the vmlinux buildid. I see the following:

[ 551.435942][ T1803] test_printf: loaded.
[ 551.436667][ T1803] ------------[ cut here ]------------
[ 551.437561][ T1803] kernel BUG at lib/test_printf.c:689!
[ 551.438352][ T1803] invalid opcode: 0000 [#1] SMP NOPTI
[ 551.438359][ T1803] CPU: 3 PID: 1803 Comm: modprobe Kdump: loaded Tainted: G E 5.12.0-rc6-default+ #176 e51781e52aaf4d6dfea7a18574c104c8bfd7c37f
[ 551.438363][ T1803] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014
[ 551.438365][ T1803] RIP: 0010:test_printf_init+0x561/0xc99 [test_printf c2388ff0552611501b4d2ad58d8e5ca441d9a350]
[ 551.443090][ T1803] Code: 00 48 c7 c7 b8 36 1b c0 e8 19 f9 ff ff b9 ab 00 00 00 48 c7 c2 93 36 1b c0 be 08 00 00 00 48 c7 c7 af 36 1b c0 e8 fc f8 ff ff <0f> 0b 8b 05 44 07 00 00 8b 35 3a 07 00 00 8b 1d 3c 07 00 00 85 c0
[ 551.443094][ T1803] RSP: 0018:ffffb62c0039bc78 EFLAGS: 00010282
[ 551.443096][ T1803] RAX: 0000000000000000 RBX: ffffb62c0039bc80 RCX: ffffd62bffc00b70
[ 551.443098][ T1803] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffa0352fd5
[ 551.443099][ T1803] RBP: ffffffffc01b7367 R08: 0000000000000001 R09: 0000000000000001
[ 551.443100][ T1803] R10: 0000000000000000 R11: 0000000000000001 R12: ffff9bc08c87c820
[ 551.443101][ T1803] R13: 0000000000000001 R14: ffff9bc0d2798480 R15: ffffb62c0039be90
[ 551.443102][ T1803] FS: 00007f5767485b80(0000) GS:ffff9bc0ffc00000(0000) knlGS:0000000000000000
[ 551.443103][ T1803] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 551.443105][ T1803] CR2: 00007f5766b36ef0 CR3: 0000000100368004 CR4: 0000000000370ee0
[ 551.443108][ T1803] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 551.443108][ T1803] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 551.443109][ T1803] Call Trace:
[ 551.443113][ T1803] ? __test+0x13c/0x149 [test_printf]
[ 551.443116][ T1803] ? rcu_read_lock_sched_held+0x52/0x80
[ 551.443120][ T1803] do_one_initcall+0x5b/0x2d0
[ 551.443125][ T1803] do_init_module+0x5b/0x21c
[ 551.443127][ T1803] load_module+0x1eaa/0x23c0
[ 551.443130][ T1803] ? show_modinfo_version+0x30/0x30
[ 551.443134][ T1803] ? __do_sys_finit_module+0xad/0x110
[ 551.443135][ T1803] __do_sys_finit_module+0xad/0x110
[ 551.443138][ T1803] do_syscall_64+0x33/0x40
[ 551.443139][ T1803] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 551.443143][ T1803] RIP: 0033:0x7f5766b5b2a9
[

Note that it still does not show the build id for the module. It fails
in the module init call and the build id should be already initialized
at this stage.

One more thing. I am not familiar with the elf-related code.
Is it safe to access (nhdr + 1)? Do we need a check that
it is still withing the given section?

Best Regards,
Petr