Commit 2d49b721 authored Jun 10, 2021 by Peter Zijlstra

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: 9bc0bb50 ("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>

parent 584fd3b3

tools/objtool/arch/x86/decode.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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;