Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752823AbdFGXD4 (ORCPT ); Wed, 7 Jun 2017 19:03:56 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:50466 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752413AbdFGXDt (ORCPT ); Wed, 7 Jun 2017 19:03:49 -0400 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux@roeck-us.net Cc: "Steven Rostedt (Red Hat)" , Willy Tarreau Subject: [PATCH 3.10 034/250] ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it Date: Thu, 8 Jun 2017 00:57:00 +0200 Message-Id: <1496876436-32402-35-git-send-email-w@1wt.eu> X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a In-Reply-To: <1496876436-32402-1-git-send-email-w@1wt.eu> References: <1496876436-32402-1-git-send-email-w@1wt.eu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1460 Lines: 41 From: "Steven Rostedt (Red Hat)" commit 847fa1a6d3d00f3bdf68ef5fa4a786f644a0dd67 upstream. With new binutils, gcc may get smart with its optimization and change a jmp from a 5 byte jump to a 2 byte one even though it was jumping to a global function. But that global function existed within a 2 byte radius, and gcc was able to optimize it. Unfortunately, that jump was also being modified when function graph tracing begins. Since ftrace expected that jump to be 5 bytes, but it was only two, it overwrote code after the jump, causing a crash. This was fixed for x86_64 with commit 8329e818f149, with the same subject as this commit, but nothing was done for x86_32. Fixes: d61f82d06672 ("ftrace: use dynamic patching for updating mcount calls") Reported-by: Colin Ian King Tested-by: Colin Ian King Signed-off-by: Steven Rostedt Signed-off-by: Willy Tarreau --- arch/x86/kernel/entry_32.S | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S index 5c38e2b..c502340 100644 --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -1103,8 +1103,8 @@ ftrace_graph_call: jmp ftrace_stub #endif -.globl ftrace_stub -ftrace_stub: +/* This is weak to keep gas from relaxing the jumps */ +WEAK(ftrace_stub) ret END(ftrace_caller) -- 2.8.0.rc2.1.gbe9624a