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: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lkml.kernel.org/r/20220405075531.GB30877@worktop.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2022-03-28 13:13:41 +02:00
Родитель 7a53f40890
Коммит be8a096521
1 изменённых файлов: 1 добавлений и 0 удалений

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@ -412,6 +412,7 @@ static void emit_indirect_jump(u8 **pprog, int reg, u8 *ip)
EMIT_LFENCE(); EMIT_LFENCE();
EMIT2(0xFF, 0xE0 + reg); EMIT2(0xFF, 0xE0 + reg);
} else if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) { } else if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) {
OPTIMIZER_HIDE_VAR(reg);
emit_jump(&prog, &__x86_indirect_thunk_array[reg], ip); emit_jump(&prog, &__x86_indirect_thunk_array[reg], ip);
} else } else
#endif #endif