From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e24smtp01.br.ibm.com (e24smtp01.br.ibm.com [32.104.18.85]) (using TLSv1.2 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3qbbHg2Z3FzDq7h for ; Fri, 1 Apr 2016 07:11:11 +1100 (AEDT) Received: from localhost by e24smtp01.br.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 31 Mar 2016 17:11:06 -0300 Received: from d24relay01.br.ibm.com (d24relay01.br.ibm.com [9.8.31.16]) by d24dlp02.br.ibm.com (Postfix) with ESMTP id 2A0A91DC006F for ; Thu, 31 Mar 2016 16:10:57 -0400 (EDT) Received: from d24av03.br.ibm.com (d24av03.br.ibm.com [9.8.31.95]) by d24relay01.br.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u2VJ8ket5058632 for ; Thu, 31 Mar 2016 16:08:46 -0300 Received: from d24av03.br.ibm.com (localhost [127.0.0.1]) by d24av03.br.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u2VKB1um023554 for ; Thu, 31 Mar 2016 17:11:01 -0300 From: Thiago Jung Bauermann To: linuxppc-dev@lists.ozlabs.org Cc: "Naveen N. Rao" , Thiago Jung Bauermann , Ananth N Mavinakayanahalli , Michael Ellerman Subject: [PATCH] powerpc/kprobes: Remove kretprobe_trampoline_holder. Date: Thu, 31 Mar 2016 17:10:40 -0300 Message-Id: <1459455040-25671-1-git-send-email-bauerman@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Cc: Michael Ellerman Reviewed-by: Naveen N. Rao Signed-off-by: Thiago Jung Bauermann --- 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 -- 1.9.1