[RFC][PATCH 8/9] jump_label,objtool: Generate possible statistics

[Peter Zijlstra]

        x86_64-defconfig        x86_64-allmodconfig-UBSAN-KASAN

NOP2    1641                    21796
JMP8    48                      114

NOP5    1010                    31042
JMP32   29                      91

Which results in a possible 3*(1641+48) ~ 5k saving for defconfig
and 3*(21796+114) ~ 64k saving for allmodconfig.

Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Josh Poimboeuf <jpoim...@redhat.com>
Cc: "H.J. Lu" <hjl.to...@gmail.com>
---
 tools/objtool/check.c |   43 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 41 insertions(+), 2 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -817,6 +817,8 @@ static int handle_jump_alt(struct objtoo
                           struct instruction *orig_insn,
                           struct instruction **new_insn)
 {
+       long disp;
+
        if ((orig_insn->len != 2) && (orig_insn->len != 5)) {
                WARN_FUNC("jump_label: unsupported INSN length: %d",
                                orig_insn->sec, orig_insn->offset, 
orig_insn->len);
@@ -824,9 +826,12 @@ static int handle_jump_alt(struct objtoo
        }
 
        if (orig_insn->type == INSN_NOP) {
-               long disp;
 
-               if (orig_insn->len == 2) {
+               switch (orig_insn->len) {
+               case 2:
+                       WARN_FUNC("jump_label: NOP2 present",
+                                       orig_insn->sec, orig_insn->offset);
+
                        if (special_alt->orig_sec != special_alt->new_sec) {
                                WARN_FUNC("jump_label: JMP8 crossing sections",
                                                orig_insn->sec, 
orig_insn->offset);
@@ -839,6 +844,20 @@ static int handle_jump_alt(struct objtoo
                                                orig_insn->sec, 
orig_insn->offset);
                                return -1;
                        }
+                       break;
+
+               case 5:
+                       if (special_alt->orig_sec == special_alt->new_sec) {
+                               disp = special_alt->new_off - 
(special_alt->orig_off + 2);
+                               if ((disp>>31) == (disp>>7)) {
+                                       WARN_FUNC("jump_label: NOP2 possible",
+                                                       orig_insn->sec, 
orig_insn->offset);
+                                       break;
+                               }
+                       }
+                       WARN_FUNC("jump_label: NOP5 present",
+                                       orig_insn->sec, orig_insn->offset);
+                       break;
                }
 
                return 0;
@@ -850,6 +869,26 @@ static int handle_jump_alt(struct objtoo
                return -1;
        }
 
+       switch (orig_insn->len) {
+       case 2:
+               WARN_FUNC("jump_label: JMP8 present",
+                               orig_insn->sec, orig_insn->offset);
+               break;
+
+       case 5:
+               if (special_alt->orig_sec == special_alt->new_sec) {
+                       disp = special_alt->new_off - (special_alt->orig_off + 
2);
+                       if ((disp>>31) == (disp>>7)) {
+                               WARN_FUNC("jump_label: JMP8 possible",
+                                               orig_insn->sec, 
orig_insn->offset);
+                               break;
+                       }
+               }
+               WARN_FUNC("jump_label: JMP32 present",
+                               orig_insn->sec, orig_insn->offset);
+               break;
+       }
+
        *new_insn = list_next_entry(orig_insn, list);
        return 0;
 }