From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [103.22.144.67]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3qWbvb1sz9zDq71 for ; Fri, 25 Mar 2016 19:24:59 +1100 (AEDT) In-Reply-To: <1458839824-27844-1-git-send-email-bauerman@linux.vnet.ibm.com> To: Thiago Jung Bauermann , linuxppc-dev@lists.ozlabs.org From: Michael Ellerman Cc: Thiago Jung Bauermann Subject: Re: Make kretprobe_trampoline symbol look like a function. Message-Id: <3qWbvb0yVwz9sdm@ozlabs.org> Date: Fri, 25 Mar 2016 19:24:59 +1100 (AEDT) List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2016-24-03 at 17:17:04 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, during symbol deduplication kretprobe_trampoline is > used instead of .kretprobe_trampoline_holder, making all vmlinux symbols match > /proc/kallsyms and the testcase passes. Thanks, good change log. > Alternatively, I just noticed that commit c1c355c was merged and it > gets rid of kretprobe_trampoline_holder altogether on x86. I believe that > would fix this problem as well, but I don't know enough about kprobes to > know whether kretprobe_trampoline_holder has any use on powerpc. I don't see any reason why we need it on powerpc. So can you try removing kretprobe_trampoline_holder and check that kretprobes still work. And then confirm that it also fixes this bug? cheers