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649ea4d5a6
kernel_optimize_test/tools/objtool
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Josh Poimboeuf 649ea4d5a6 objtool: Assume unannotated UD2 instructions are dead ends 
Arnd reported some false positive warnings with GCC 7:

  drivers/hid/wacom_wac.o: warning: objtool: wacom_bpt3_touch()+0x2a5: stack state mismatch: cfa1=7+8 cfa2=6+16
  drivers/iio/adc/vf610_adc.o: warning: objtool: vf610_adc_calculate_rates() falls through to next function vf610_adc_sample_set()
  drivers/pwm/pwm-hibvt.o: warning: objtool: hibvt_pwm_get_state() falls through to next function hibvt_pwm_remove()
  drivers/pwm/pwm-mediatek.o: warning: objtool: mtk_pwm_config() falls through to next function mtk_pwm_enable()
  drivers/spi/spi-bcm2835.o: warning: objtool: .text: unexpected end of section
  drivers/spi/spi-bcm2835aux.o: warning: objtool: .text: unexpected end of section
  drivers/watchdog/digicolor_wdt.o: warning: objtool: dc_wdt_get_timeleft() falls through to next function dc_wdt_restart()

When GCC 7 detects a potential divide-by-zero condition, it sometimes
inserts a UD2 instruction for the case where the divisor is zero,
instead of letting the hardware trap on the divide instruction.

Objtool doesn't consider UD2 to be fatal unless it's annotated with
unreachable().  So it considers the GCC-generated UD2 to be non-fatal,
and it tries to follow the control flow past the UD2 and gets
confused.

Previously, objtool *did* assume UD2 was always a dead end.  That
changed with the following commit:

  d1091c7fa3 ("objtool: Improve detection of BUG() and other dead ends")

The motivation behind that change was that Peter was planning on using
UD2 for __WARN(), which is *not* a dead end.  However, it turns out
that some emulators rely on UD2 being fatal, so he ended up using
'ud0' instead:

  9a93848fe7 ("x86/debug: Implement __WARN() using UD0")

For GCC 4.5+, it should be safe to go back to the previous assumption
that UD2 is fatal, even when it's not annotated with unreachable().

But for pre-4.5 versions of GCC, the unreachable() macro isn't
supported, so such cases of UD2 need to be explicitly annotated as
reachable.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: d1091c7fa3 ("objtool: Improve detection of BUG() and other dead ends")
Link: http://lkml.kernel.org/r/e57fa9dfede25f79487da8126ee9cdf7b856db65.1501188854.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-07-28 08:33:32 +02:00
..
arch/x86 objtool: Assume unannotated UD2 instructions are dead ends 2017-07-28 08:33:32 +02:00
Documentation objtool: Add ORC unwind table generation 2017-07-18 10:57:43 +02:00
.gitignore
arch.h objtool: Assume unannotated UD2 instructions are dead ends 2017-07-28 08:33:32 +02:00
Build objtool: Add ORC unwind table generation 2017-07-18 10:57:43 +02:00
builtin-check.c objtool: Fix gcov check for older versions of GCC 2017-07-25 11:12:45 +02:00
builtin-orc.c objtool: Fix gcov check for older versions of GCC 2017-07-25 11:12:45 +02:00
builtin.h objtool: Add ORC unwind table generation 2017-07-18 10:57:43 +02:00
cfi.h objtool: Implement stack validation 2.0 2017-06-30 10:19:19 +02:00
check.c objtool: Assume unannotated UD2 instructions are dead ends 2017-07-28 08:33:32 +02:00
check.h objtool: Fix gcov check for older versions of GCC 2017-07-25 11:12:45 +02:00
elf.c objtool: Add ORC unwind table generation 2017-07-18 10:57:43 +02:00
elf.h objtool: Add ORC unwind table generation 2017-07-18 10:57:43 +02:00
Makefile objtool, x86: Add facility for asm code to provide unwind hints 2017-07-18 10:57:44 +02:00
objtool.c objtool: Add ORC unwind table generation 2017-07-18 10:57:43 +02:00
orc_dump.c objtool: Add ORC unwind table generation 2017-07-18 10:57:43 +02:00
orc_gen.c objtool: Add ORC unwind table generation 2017-07-18 10:57:43 +02:00
orc_types.h objtool, x86: Add facility for asm code to provide unwind hints 2017-07-18 10:57:44 +02:00
orc.h objtool: Add ORC unwind table generation 2017-07-18 10:57:43 +02:00
special.c objtool: Implement stack validation 2.0 2017-06-30 10:19:19 +02:00
special.h
warn.h objtool: Implement stack validation 2.0 2017-06-30 10:19:19 +02:00