https://github.com/torvalds/linux
Revision b33c8ff4431a343561e2319f17c14286f2aa52e2 authored by Arnd Bergmann on 12 February 2016, 21:26:42 UTC, committed by Steven Rostedt on 15 February 2016, 18:06:00 UTC
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 <nico@linaro.org> Fixes: ab3c9c686e22 ("branch tracer, intel-iommu: fix build with CONFIG_BRANCH_TRACER=y") Cc: stable@vger.kernel.org # v2.6.30+ Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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Tip revision: b33c8ff4431a343561e2319f17c14286f2aa52e2 authored by Arnd Bergmann on 12 February 2016, 21:26:42 UTC
tracing: Fix freak link error caused by branch tracer
tracing: Fix freak link error caused by branch tracer
Tip revision: b33c8ff
File | Mode | Size |
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Documentation | ||
arch | ||
block | ||
certs | ||
crypto | ||
drivers | ||
firmware | ||
fs | ||
include | ||
init | ||
ipc | ||
kernel | ||
lib | ||
mm | ||
net | ||
samples | ||
scripts | ||
security | ||
sound | ||
tools | ||
usr | ||
virt | ||
.get_maintainer.ignore | -rw-r--r-- | 31 bytes |
.gitignore | -rw-r--r-- | 1.2 KB |
.mailmap | -rw-r--r-- | 5.5 KB |
COPYING | -rw-r--r-- | 18.3 KB |
CREDITS | -rw-r--r-- | 95.4 KB |
Kbuild | -rw-r--r-- | 2.6 KB |
Kconfig | -rw-r--r-- | 252 bytes |
MAINTAINERS | -rw-r--r-- | 337.0 KB |
Makefile | -rw-r--r-- | 53.7 KB |
README | -rw-r--r-- | 18.2 KB |
REPORTING-BUGS | -rw-r--r-- | 7.3 KB |
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