Hello,
People seem to be considering patches for next, so this looks like a good
moment to ping about this one.
--
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center
Am Donnerstag, 31 März 2016, 17:10:40 schrieb Thiago Jung Bauermann:
> 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.
>
> Commit c1c355ce14c0 ("x86/kprobes: Get rid of
> kretprobe_trampoline_holder()") gets rid of kretprobe_trampoline_holder
> altogether on x86. This commit does the same on powerpc. This change
> introduces no regressions on the perf and ftracetest testsuite results.
>
> Cc: Ananth N Mavinakayanahalli <ana...@in.ibm.com>
> Cc: Michael Ellerman <m...@ellerman.id.au>
> Reviewed-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
> Signed-off-by: Thiago Jung Bauermann <bauer...@linux.vnet.ibm.com>
> ---
> arch/powerpc/kernel/kprobes.c | 11 +++++------
> 1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index 7c053f281406..417c0eadd094 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -278,12 +278,11 @@ no_kprobe:
> * - When the probed function returns, this probe
> * causes the handlers to fire
> */
> -static void __used kretprobe_trampoline_holder(void)
> -{
> - asm volatile(".global kretprobe_trampoline\n"
> - "kretprobe_trampoline:\n"
> - "nop\n");
> -}
> +asm(".global kretprobe_trampoline\n"
> + ".type kretprobe_trampoline, @function\n"
> + "kretprobe_trampoline:\n"
> + "nop\n"
> + ".size kretprobe_trampoline, .-kretprobe_trampoline\n");
>
> /*
> * Called when the probe at kretprobe trampoline is hit
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