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linux-stable/tools/objtool
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Josh Poimboeuf cd77849a69 objtool: Fix GCC 8 cold subfunction detection for aliased functions 
The kbuild test robot reported the following issue:

  kernel/time/posix-stubs.o: warning: objtool: sys_ni_posix_timers.cold.1()+0x0: unreachable instruction

This file creates symbol aliases for the sys_ni_posix_timers() function.
So there are multiple ELF function symbols for the same function:

  23: 0000000000000150     26 FUNC    GLOBAL DEFAULT        1 __x64_sys_timer_create
  24: 0000000000000150     26 FUNC    GLOBAL DEFAULT        1 sys_ni_posix_timers
  25: 0000000000000150     26 FUNC    GLOBAL DEFAULT        1 __ia32_sys_timer_create
  26: 0000000000000150     26 FUNC    GLOBAL DEFAULT        1 __x64_sys_timer_gettime

Here's the corresponding cold subfunction:

  11: 0000000000000000     45 FUNC    LOCAL  DEFAULT        6 sys_ni_posix_timers.cold.1

When analyzing overlapping functions, objtool only looks at the first
one in the symbol list.  The rest of the functions are basically ignored
because they point to instructions which have already been analyzed.

So in this case it analyzes the __x64_sys_timer_create() function, but
then it fails to recognize that its cold subfunction is
sys_ni_posix_timers.cold.1(), because the names are different.

Make the subfunction detection a little smarter by associating each
subfunction with the first function which jumps to it, since that's the
one which will be analyzed.

Unfortunately we still have to leave the original subfunction detection
code in place, thanks to GCC switch tables.  (See the comment for more
details.)

Fixes: 13810435b9 ("objtool: Support GCC 8's cold subfunctions")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/d3ba52662cbc8e3a64a3b64d44b4efc5674fd9ab.1527855808.git.jpoimboe@redhat.com
2018-06-06 14:45:22 +02:00
..
arch/x86 objtool, kprobes/x86: Sync the latest <asm/insn.h> header with tools/objtool/arch/x86/include/asm/insn.h 2018-05-14 10:15:54 +02:00
Documentation x86/asm: Fix inline asm call constraints for Clang 2017-09-23 15:06:20 +02:00
.gitignore objtool: Move synced files to their original relative locations 2017-11-07 10:48:23 +01:00
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: Add module specific retpoline rules 2018-02-21 09:05:05 +01:00
builtin-orc.c objtool: Use existing global variables for options 2018-02-21 09:05:04 +01:00
builtin.h objtool: Add module specific retpoline rules 2018-02-21 09:05:05 +01:00
cfi.h objtool: Handle GCC stack pointer adjustment bug 2017-08-30 10:48:41 +02:00
check.c objtool: Fix GCC 8 cold subfunction detection for aliased functions 2018-06-06 14:45:22 +02:00
check.h objtool: Add retpoline validation 2018-02-21 09:05:04 +01:00
elf.c objtool: Support GCC 8's cold subfunctions 2018-05-14 10:20:53 +02:00
elf.h objtool: Support GCC 8's cold subfunctions 2018-05-14 10:20:53 +02:00
Makefile objtool: Support HOSTCFLAGS and HOSTLDFLAGS 2018-04-17 07:59:42 +02:00
objtool.c objtool: Print top level commands on incorrect usage 2017-10-18 15:22:26 +02:00
orc.h objtool: Move synced files to their original relative locations 2017-11-07 10:48:23 +01:00
orc_dump.c objtool: Fix 64-bit build on 32-bit host 2017-12-06 22:38:14 +01:00
orc_gen.c objtool: Warn on stripped section symbol 2018-01-30 15:09:23 +01:00
special.c objtool: Implement stack validation 2.0 2017-06-30 10:19:19 +02:00
special.h
sync-check.sh objtool: Move kernel headers/code sync check to a script 2017-11-07 10:48:34 +01:00
warn.h objtool: Implement stack validation 2.0 2017-06-30 10:19:19 +02:00