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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: 9bc0bb5072 ("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>
This commit is contained in:
Peter Zijlstra 2021-06-10 09:04:29 +02:00
parent 584fd3b318
commit 2d49b721dc
1 changed files with 4 additions and 0 deletions
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4
tools/objtool/arch/x86/decode.c
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@ -747,6 +747,10 @@ int arch_rewrite_retpolines(struct objtool_file *file)
list_for_each_entry(insn, &file->retpoline_call_list, call_node) {
if (insn->type != INSN_JUMP_DYNAMIC &&
insn->type != INSN_CALL_DYNAMIC)
continue;
if (!strcmp(insn->sec->name, ".text.__x86.indirect_thunk"))
continue;