Files
android_kernel_xiaomi_sm8450/include/linux
Arnd Bergmann b33c8ff443 tracing: Fix freak link error caused by branch tracer
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: ab3c9c686e ("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>
2016-02-15 13:06:00 -05:00
..
2016-02-04 18:26:08 +01:00
2015-10-17 21:22:08 -07:00
2015-10-07 18:08:15 +01:00
2016-01-05 18:04:58 +01:00
2015-11-16 15:41:49 +00:00
2015-12-23 08:37:10 -07:00
2015-08-03 12:01:54 -04:00
2015-12-22 09:38:34 -07:00
2015-12-06 12:46:31 +01:00
2015-10-07 16:02:49 -07:00
2015-09-04 16:54:41 -07:00
2016-01-30 13:35:32 -08:00
2015-10-18 10:14:39 -07:00
2015-10-31 19:05:59 -04:00
2016-01-08 01:12:06 +01:00
2015-10-30 01:47:27 -04:00
2015-12-28 13:41:50 +01:00
2016-01-15 17:56:32 -08:00
2015-11-25 09:22:00 -07:00
2015-10-23 05:44:28 -07:00
2016-01-20 17:09:18 -08:00
2015-10-01 15:06:43 +02:00
2015-12-14 10:03:46 +01:00
2015-06-25 12:06:45 +02:00
2015-07-28 08:50:42 +01:00
2016-01-15 17:56:32 -08:00
2016-01-15 17:56:32 -08:00
2016-01-15 17:56:32 -08:00
2015-10-27 18:55:31 -07:00
2016-02-03 08:28:43 -08:00
2016-02-03 08:28:43 -08:00
2015-10-20 22:10:45 +08:00
2015-07-21 10:39:05 -07:00
2015-06-25 04:20:04 -04:00
2016-01-04 13:19:55 -05:00
2015-09-10 13:29:01 -07:00
2015-09-10 13:29:01 -07:00
2016-01-22 17:02:18 -08:00
2016-02-11 18:35:48 -08:00
2016-02-11 18:35:48 -08:00
2016-01-07 14:31:27 -05:00
2015-10-06 17:08:19 +02:00
2015-10-22 08:59:18 -07:00
2015-11-16 09:23:47 +01:00
2016-01-10 22:13:15 -05:00
2015-12-13 19:59:48 -08:00
2016-01-04 16:11:11 -05:00
2016-02-09 04:28:06 -05:00
2016-01-04 10:20:19 -05:00
2015-06-25 17:00:39 -07:00
2015-11-05 14:36:09 -05:00
2016-01-15 22:34:39 +01:00
2015-08-17 11:25:28 -07:00
2015-10-01 09:57:59 -07:00
2015-10-19 01:01:21 +02:00
2015-11-23 09:44:58 +01:00
2015-12-21 15:28:11 -07:00
2016-01-12 20:47:02 +02:00
2016-01-15 17:56:32 -08:00
2016-01-14 16:00:49 -08:00
2015-12-03 07:24:29 -08:00
2015-09-08 15:35:28 -07:00