From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e24smtp02.br.ibm.com (e24smtp02.br.ibm.com [32.104.18.86]) (using TLSv1.2 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3qlhjj120ZzDq62 for ; Thu, 14 Apr 2016 10:43:20 +1000 (AEST) Received: from localhost by e24smtp02.br.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 13 Apr 2016 21:43:16 -0300 Received: from d24relay01.br.ibm.com (d24relay01.br.ibm.com [9.8.31.16]) by d24dlp02.br.ibm.com (Postfix) with ESMTP id 3570E1DC006E for ; Wed, 13 Apr 2016 20:43:08 -0400 (EDT) Received: from d24av05.br.ibm.com (d24av05.br.ibm.com [9.18.232.44]) by d24relay01.br.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u3DNexPd3879064 for ; Wed, 13 Apr 2016 20:40:59 -0300 Received: from d24av05.br.ibm.com (localhost [127.0.0.1]) by d24av05.br.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u3E0hDti001414 for ; Wed, 13 Apr 2016 20:43:13 -0400 From: Thiago Jung Bauermann To: linuxppc-dev@lists.ozlabs.org Cc: "Naveen N. Rao" Subject: Re: [PATCH] powerpc/kprobes: Remove kretprobe_trampoline_holder. Date: Wed, 13 Apr 2016 21:43:10 -0300 Message-ID: <1649722.nzyaxjufOM@hactar> In-Reply-To: <1459455040-25671-1-git-send-email-bauerman@linux.vnet.ibm.com> References: <1459455040-25671-1-git-send-email-bauerman@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hello, People seem to be considering patches for next, so this looks like a go= od=20 moment to ping about this one. --=20 []'s Thiago Jung Bauermann IBM Linux Technology Center Am Donnerstag, 31 M=E4rz 2016, 17:10:40 schrieb Thiago Jung Bauermann: > Fixes the following testsuite failure: >=20 > $ 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.kallsym= s] > f000000000000000-ffffffffffffffff 3000000000010000 [kernel.kallsym= s] > test child finished with -1 > ---- end ---- > vmlinux symtab matches kallsyms: FAILED! >=20 > The problem is that the kretprobe_trampoline symbol looks like this: >=20 > $ eu-readelf -s /boot/vmlinux G kretprobe_trampoline > 2431: c000000001302368 24 NOTYPE LOCAL DEFAULT 37 > kretprobe_trampoline_holder 2432: c00000000003d300 8 FUNC LOC= AL=20 > DEFAULT 1 .kretprobe_trampoline_holder 97543: c00000000003d300= =20 > 0 NOTYPE GLOBAL DEFAULT 1 kretprobe_trampoline >=20 > 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_FU= NC > 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-zer= o > size (as determined by choose_best_symbol). >=20 > With this patch, all vmlinux symbols match /proc/kallsyms and the > testcase passes. >=20 > Commit c1c355ce14c0 ("x86/kprobes: Get rid of > kretprobe_trampoline_holder()") gets rid of kretprobe_trampoline_hold= er > altogether on x86. This commit does the same on powerpc. This change > introduces no regressions on the perf and ftracetest testsuite result= s. >=20 > 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(-) >=20 > diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kpro= bes.c > index 7c053f281406..417c0eadd094 100644 > --- a/arch/powerpc/kernel/kprobes.c > +++ b/arch/powerpc/kernel/kprobes.c > @@ -278,12 +278,11 @@ no_kprobe: > * =09- When the probed function returns, this probe > * =09=09causes the handlers to fire > */ > -static void __used kretprobe_trampoline_holder(void) > -{ > -=09asm volatile(".global kretprobe_trampoline\n" > -=09=09=09"kretprobe_trampoline:\n" > -=09=09=09"nop\n"); > -} > +asm(".global kretprobe_trampoline\n" > +=09".type kretprobe_trampoline, @function\n" > +=09"kretprobe_trampoline:\n" > +=09"nop\n" > +=09".size kretprobe_trampoline, .-kretprobe_trampoline\n"); >=20 > /* > * Called when the probe at kretprobe trampoline is hit