objtool: Support unoptimized frame pointer setup

Arnd Bergmann reported a bunch of warnings like:

  crypto/jitterentropy.o: warning: objtool: jent_fold_time()+0x3b: call without frame pointer save/setup
  crypto/jitterentropy.o: warning: objtool: jent_stuck()+0x1d: call without frame pointer save/setup
  crypto/jitterentropy.o: warning: objtool: jent_unbiased_bit()+0x15: call without frame pointer save/setup
  crypto/jitterentropy.o: warning: objtool: jent_read_entropy()+0x32: call without frame pointer save/setup
  crypto/jitterentropy.o: warning: objtool: jent_entropy_collector_free()+0x19: call without frame pointer save/setup

and

  arch/x86/events/core.o: warning: objtool: collect_events uses BP as a scratch register
  arch/x86/events/core.o: warning: objtool: events_ht_sysfs_show()+0x22: call without frame pointer save/setup

With certain rare configurations, GCC sometimes sets up the frame
pointer with:

  lea    (%rsp),%rbp

instead of:

  mov    %rsp,%rbp

The instructions are equivalent, so treat the former like the latter.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/a468af8b28a69b83fffc6d7668be9b6fcc873699.1506526584.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 0f22768c0d4d0c26ae86ad3e51b49bd760f4ed6a..34a579f806e390337bdee738ae507364c02e7ad7 100644 (file)
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -284,11 +284,16 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
        case 0x8d:
                if (sib == 0x24 && rex_w && !rex_b && !rex_x) {
 
-                       /* lea disp(%rsp), reg */
                        *type = INSN_STACK;
-                       op->src.type = OP_SRC_ADD;
+                       if (!insn.displacement.value) {
+                               /* lea (%rsp), reg */
+                               op->src.type = OP_SRC_REG;
+                       } else {
+                               /* lea disp(%rsp), reg */
+                               op->src.type = OP_SRC_ADD;
+                               op->src.offset = insn.displacement.value;
+                       }
                        op->src.reg = CFI_SP;
-                       op->src.offset = insn.displacement.value;
                        op->dest.type = OP_DEST_REG;
                        op->dest.reg = op_to_cfi_reg[modrm_reg][rex_r];