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mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-23 12:43:55 +08:00
linux-next/tools/objtool
Josh Poimboeuf 7e578441a4 objtool: Add workaround for GCC switch jump table bug
GCC has a rare quirk, currently only seen in three driver functions in
the kernel, and only with certain obscure non-distro configs, which can
cause objtool to produce "unreachable instruction" false positive
warnings.

As part of an optimization, GCC makes a copy of an existing switch jump
table, modifies it, and then hard-codes the jump (albeit with an
indirect jump) to use a single entry in the table.  The rest of the jump
table and some of its jump targets remain as dead code.

In such a case we can just crudely ignore all unreachable instruction
warnings for the entire object file.  Ideally we would just ignore them
for the function, but that would require redesigning the code quite a
bit.  And honestly that's just not worth doing: unreachable instruction
warnings are of questionable value anyway, and this is a very rare
issue.

kbuild reports:

  https://lkml.kernel.org/r/201603231906.LWcVUpxm%25fengguang.wu@intel.com
  https://lkml.kernel.org/r/201603271114.K9i45biy%25fengguang.wu@intel.com
  https://lkml.kernel.org/r/201603291058.zuJ6ben1%25fengguang.wu@intel.com

GCC bug:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70604

Reported-by: kbuild test robot <fengguang.wu@intel.com>
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>
Link: http://lkml.kernel.org/r/700fa029bbb0feff34f03ffc69d666a3c3b57a61.1460663532.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-15 11:42:13 +02:00
..
arch/x86 x86/asm/decoder: Use explicitly signed chars 2016-03-03 16:13:00 +01:00
Documentation objtool: Add tool to perform compile-time stack metadata validation 2016-02-29 08:35:12 +01:00
.gitignore objtool: Add tool to perform compile-time stack metadata validation 2016-02-29 08:35:12 +01:00
arch.h objtool: Add tool to perform compile-time stack metadata validation 2016-02-29 08:35:12 +01:00
Build objtool: Add tool to perform compile-time stack metadata validation 2016-02-29 08:35:12 +01:00
builtin-check.c objtool: Add workaround for GCC switch jump table bug 2016-04-15 11:42:13 +02:00
builtin.h objtool: Add tool to perform compile-time stack metadata validation 2016-02-29 08:35:12 +01:00
elf.c objtool: Add several performance improvements 2016-03-09 10:48:10 +01:00
elf.h objtool: Add several performance improvements 2016-03-09 10:48:10 +01:00
Makefile objtool: Compile with debugging symbols 2016-03-09 10:48:08 +01:00
objtool.c objtool: Add tool to perform compile-time stack metadata validation 2016-02-29 08:35:12 +01:00
special.c objtool: Add tool to perform compile-time stack metadata validation 2016-02-29 08:35:12 +01:00
special.h objtool: Add tool to perform compile-time stack metadata validation 2016-02-29 08:35:12 +01:00
warn.h objtool: Add tool to perform compile-time stack metadata validation 2016-02-29 08:35:12 +01:00