powerpc/kprobes: Remove kretprobe_trampoline_holder.

[Michael Ellerman]

On Thu, 2016-31-03 at 20:10:40 UTC, 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.
> 
> 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 <ananth at in.ibm.com>
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Reviewed-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
> Signed-off-by: Thiago Jung Bauermann <bauerman at linux.vnet.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/61ed9cfb1b0951a3b4b98dd8bf

cheers