objtool: Only rewrite unconditional retpoline thunk calls
authorPeter Zijlstra <peterz@infradead.org>
Thu, 10 Jun 2021 07:04:29 +0000 (09:04 +0200)
committerPeter Zijlstra <peterz@infradead.org>
Fri, 11 Jun 2021 06:53:06 +0000 (08:53 +0200)
commit2d49b721dc18c113d5221f4cf5a6104eb66cb7f2
treeab75c8cfd9dafa5f54af3988bcb7c595380e307c
parent584fd3b31889852d0d6f3dd1e3d8e9619b660d2c
objtool: Only rewrite unconditional retpoline thunk calls

It turns out that the compilers generate conditional branches to the
retpoline thunks like:

  5d5:   0f 85 00 00 00 00       jne    5db <cpuidle_reflect+0x22>
5d7: R_X86_64_PLT32     __x86_indirect_thunk_r11-0x4

while the rewrite can only handle JMP/CALL to the thunks. The result
is the alternative wrecking the code. Make sure to skip writing the
alternatives for conditional branches.

Fixes: 9bc0bb50727c ("objtool/x86: Rewrite retpoline thunk calls")
Reported-by: Lukasz Majczak <lma@semihalf.com>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
tools/objtool/arch/x86/decode.c