Commit be8a0965 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

x86,bpf: Avoid IBT objtool warning 



Clang can inline emit_indirect_jump() and then folds constants, which
results in:

  | vmlinux.o: warning: objtool: emit_bpf_dispatcher()+0x6a4: relocation to !ENDBR: .text.__x86.indirect_thunk+0x40
  | vmlinux.o: warning: objtool: emit_bpf_dispatcher()+0x67d: relocation to !ENDBR: .text.__x86.indirect_thunk+0x40
  | vmlinux.o: warning: objtool: emit_bpf_tail_call_indirect()+0x386: relocation to !ENDBR: .text.__x86.indirect_thunk+0x20
  | vmlinux.o: warning: objtool: emit_bpf_tail_call_indirect()+0x35d: relocation to !ENDBR: .text.__x86.indirect_thunk+0x20

Suppress the optimization such that it must emit a code reference to
the __x86_indirect_thunk_array[] base.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lkml.kernel.org/r/20220405075531.GB30877@worktop.programming.kicks-ass.net
parent 7a53f408

arch/x86/net/bpf_jit_comp.c

+1 −0
Original line number Diff line number Diff line
@@ -412,6 +412,7 @@ static void emit_indirect_jump(u8 **pprog, int reg, u8 *ip) 
		EMIT_LFENCE();

		EMIT2(0xFF, 0xE0 + reg);

	} else if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) {

		OPTIMIZER_HIDE_VAR(reg);

		emit_jump(&prog, &__x86_indirect_thunk_array[reg], ip);

	} else

#endif