Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965137AbcCIXdO (ORCPT ); Wed, 9 Mar 2016 18:33:14 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:41056 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934661AbcCIXSJ (ORCPT ); Wed, 9 Mar 2016 18:18:09 -0500 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Arnd Bergmann , Steven Rostedt , Kamal Mostafa Subject: [PATCH 3.13.y-ckt 094/138] tracing: Fix freak link error caused by branch tracer Date: Wed, 9 Mar 2016 15:13:41 -0800 Message-Id: <1457565265-15195-95-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.0 In-Reply-To: <1457565265-15195-1-git-send-email-kamal@canonical.com> References: <1457565265-15195-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.13 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3033 Lines: 74 3.13.11-ckt36 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Arnd Bergmann commit b33c8ff4431a343561e2319f17c14286f2aa52e2 upstream. In my randconfig tests, I came across a bug that involves several components: * gcc-4.9 through at least 5.3 * CONFIG_GCOV_PROFILE_ALL enabling -fprofile-arcs for all files * CONFIG_PROFILE_ALL_BRANCHES overriding every if() * The optimized implementation of do_div() that tries to replace a library call with an division by multiplication * code in drivers/media/dvb-frontends/zl10353.c doing u32 adc_clock = 450560; /* 45.056 MHz */ if (state->config.adc_clock) adc_clock = state->config.adc_clock; do_div(value, adc_clock); In this case, gcc fails to determine whether the divisor in do_div() is __builtin_constant_p(). In particular, it concludes that __builtin_constant_p(adc_clock) is false, while __builtin_constant_p(!!adc_clock) is true. That in turn throws off the logic in do_div() that also uses __builtin_constant_p(), and instead of picking either the constant- optimized division, and the code in ilog2() that uses __builtin_constant_p() to figure out whether it knows the answer at compile time. The result is a link error from failing to find multiple symbols that should never have been called based on the __builtin_constant_p(): dvb-frontends/zl10353.c:138: undefined reference to `____ilog2_NaN' dvb-frontends/zl10353.c:138: undefined reference to `__aeabi_uldivmod' ERROR: "____ilog2_NaN" [drivers/media/dvb-frontends/zl10353.ko] undefined! ERROR: "__aeabi_uldivmod" [drivers/media/dvb-frontends/zl10353.ko] undefined! This patch avoids the problem by changing __trace_if() to check whether the condition is known at compile-time to be nonzero, rather than checking whether it is actually a constant. I see this one link error in roughly one out of 1600 randconfig builds on ARM, and the patch fixes all known instances. Link: http://lkml.kernel.org/r/1455312410-1058841-1-git-send-email-arnd@arndb.de Acked-by: Nicolas Pitre Fixes: ab3c9c686e22 ("branch tracer, intel-iommu: fix build with CONFIG_BRANCH_TRACER=y") Signed-off-by: Arnd Bergmann Signed-off-by: Steven Rostedt Signed-off-by: Kamal Mostafa --- include/linux/compiler.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index a2329c5..a2ce6f8 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -131,7 +131,7 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); */ #define if(cond, ...) __trace_if( (cond , ## __VA_ARGS__) ) #define __trace_if(cond) \ - if (__builtin_constant_p((cond)) ? !!(cond) : \ + if (__builtin_constant_p(!!(cond)) ? !!(cond) : \ ({ \ int ______r; \ static struct ftrace_branch_data \ -- 2.7.0