From: Michael Ellerman <mpe@ellerman.id.au>
To: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] Remove kretprobe_trampoline_holder.
Date: Tue, 29 Mar 2016 14:31:34 +1100 [thread overview]
Message-ID: <1459222294.8173.8.camel@ellerman.id.au> (raw)
In-Reply-To: <1459195592-6559-1-git-send-email-bauerman@linux.vnet.ibm.com>
On Mon, 2016-03-28 at 17:06 -0300, Thiago Jung Bauermann wrote:
> Fixes the following testsuite failure:
>
> $ sudo ./perf test -v kallsyms
> 1: vmlinux symtab matches kallsyms :
> --- start ---
> test child forked, pid 12489
> Using /proc/kcore for kernel object code
> Looking at the vmlinux_path (8 entries long)
> Using /boot/vmlinux for symbols
> 0xc00000000003d300: diff name v: .kretprobe_trampoline_holder k: kretprobe_trampoline
> Maps only in vmlinux:
> c00000000086ca38-c000000000879b6c 87ca38 [kernel].text.unlikely
> c000000000879b6c-c000000000bf0000 889b6c [kernel].meminit.text
> c000000000bf0000-c000000000c53264 c00000 [kernel].init.text
> c000000000c53264-d000000004250000 c63264 [kernel].exit.text
> d000000004250000-d000000004450000 0 [libcrc32c]
> d000000004450000-d000000004620000 0 [xfs]
> d000000004620000-d000000004680000 0 [autofs4]
> d000000004680000-d0000000046e0000 0 [x_tables]
> d0000000046e0000-d000000004780000 0 [ip_tables]
> d000000004780000-d0000000047e0000 0 [rng_core]
> d0000000047e0000-ffffffffffffffff 0 [pseries_rng]
> Maps in vmlinux with a different name in kallsyms:
> Maps only in kallsyms:
> d000000000000000-f000000000000000 1000000000010000 [kernel.kallsyms]
> f000000000000000-ffffffffffffffff 3000000000010000 [kernel.kallsyms]
> test child finished with -1
> ---- end ----
> vmlinux symtab matches kallsyms: FAILED!
>
> The problem is that the kretprobe_trampoline symbol looks like this:
>
> $ eu-readelf -s /boot/vmlinux G kretprobe_trampoline
> 2431: c000000001302368 24 NOTYPE LOCAL DEFAULT 37 kretprobe_trampoline_holder
> 2432: c00000000003d300 8 FUNC LOCAL DEFAULT 1 .kretprobe_trampoline_holder
> 97543: c00000000003d300 0 NOTYPE GLOBAL DEFAULT 1 kretprobe_trampoline
>
> Its type is NOTYPE, and its size is 0, and this is a problem because
> symbol-elf.c:dso__load_sym skips function symbols that are not STT_FUNC
> or STT_GNU_IFUNC (this is determined by elf_sym__is_function). Even
> if the type is changed to STT_FUNC, when dso__load_sym calls
> symbols__fixup_duplicate, the kretprobe_trampoline symbol is dropped in
> favour of .kretprobe_trampoline_holder because the latter has non-zero
> size (as determined by choose_best_symbol).
>
> With this patch, all vmlinux symbols match /proc/kallsyms and the
> testcase passes.
Have you tested this on an LE system? I did a quick test and it appears to be
completely broken. Basically every symbol is not found, eg:
1: vmlinux symtab matches kallsyms :
--- start ---
test child forked, pid 16222
Using /proc/kcore for kernel object code
Looking at the vmlinux_path (8 entries long)
Using /boot/vmlinux-4.5.0-11318-gdf01bc5cf4ea for symbols
0xc00000000000b428: run_init_process not on kallsyms
0xc00000000000b478: try_to_run_init_process not on kallsyms
0xc00000000000b4f8: do_one_initcall not on kallsyms
0xc00000000000b768: match_dev_by_uuid not on kallsyms
...
0xc0000000009846b8: write_mem not on kallsyms
0xc000000000984728: do_fp_store not on kallsyms
0xc000000000984828: emulate_step not on kallsyms
$ sudo grep emulate_step /proc/kallsyms
c000000000984820 T emulate_step
Notice it's off by 8. That's because of the local/global entry point on LE. So
that will need to be fixed somewhere.
cheers
next prev parent reply other threads:[~2016-03-29 3:31 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-24 17:17 [PATCH] Make kretprobe_trampoline symbol look like a function Thiago Jung Bauermann
2016-03-25 8:24 ` Michael Ellerman
2016-03-28 20:06 ` [PATCH] Remove kretprobe_trampoline_holder Thiago Jung Bauermann
2016-03-28 20:29 ` Thiago Jung Bauermann
2016-03-28 23:45 ` Michael Ellerman
2016-03-29 18:34 ` Thiago Jung Bauermann
2016-03-30 0:09 ` Michael Ellerman
2016-03-29 3:31 ` Michael Ellerman [this message]
2016-03-29 23:35 ` Thiago Jung Bauermann
2016-03-30 8:04 ` Naveen N. Rao
2016-03-30 8:46 ` Naveen N. Rao
2016-03-30 9:09 ` Michael Ellerman
2016-03-30 18:38 ` Thiago Jung Bauermann
2016-03-31 8:23 ` Naveen N. Rao
2016-03-31 20:16 ` Thiago Jung Bauermann
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