Most functions have an unconditional return at the end, like
this one:
00000000 <is_exec_fault>:
0: 81 22 04 d0 lwz r9,1232(r2)
4: 38 60 00 00 li r3,0
8: 2c 09 00 00 cmpwi r9,0
c: 4d 82 00 20 beqlr <== Conditional return
10: 80 69 00 a0 lwz r3,160(r9)
14: 54 63 00 36 clrrwi r3,r3,4
18: 68 63 04 00 xori r3,r3,1024
1c: 7c 63 00 34 cntlzw r3,r3
20: 54 63 d9 7e srwi r3,r3,5
24: 4e 80 00 20 blr <== Unconditional return
But other functions like this other one below only have
conditional returns:
00000028 <pte_update.isra.0>:
28: 81 25 00 00 lwz r9,0(r5)
2c: 2c 08 00 00 cmpwi r8,0
30: 7d 29 30 78 andc r9,r9,r6
34: 7d 27 3b 78 or r7,r9,r7
38: 54 84 65 3a rlwinm r4,r4,12,20,29
3c: 81 23 00 18 lwz r9,24(r3)
40: 41 82 00 58 beq 98 <pte_update.isra.0+0x70>
44: 7d 29 20 2e lwzx r9,r9,r4
48: 55 29 07 3a rlwinm r9,r9,0,28,29
4c: 2c 09 00 0c cmpwi r9,12
50: 41 82 00 08 beq 58 <pte_update.isra.0+0x30>
54: 39 00 00 80 li r8,128
58: 2c 08 00 01 cmpwi r8,1
5c: 90 e5 00 00 stw r7,0(r5)
60: 4d a2 00 20 beqlr+ <== Conditional return
64: 7c e9 3b 78 mr r9,r7
68: 39 40 00 00 li r10,0
6c: 39 4a 00 04 addi r10,r10,4
70: 7c 0a 40 00 cmpw r10,r8
74: 91 25 00 04 stw r9,4(r5)
78: 91 25 00 08 stw r9,8(r5)
7c: 38 a5 00 10 addi r5,r5,16
80: 91 25 ff fc stw r9,-4(r5)
84: 4c 80 00 20 bgelr <== Conditional return
88: 55 49 60 26 slwi r9,r10,12
8c: 7d 29 3a 14 add r9,r9,r7
90: 91 25 00 00 stw r9,0(r5)
94: 4b ff ff d8 b 6c <pte_update.isra.0+0x44>
98: 39 00 00 04 li r8,4
9c: 4b ff ff bc b 58 <pte_update.isra.0+0x30>
If conditional returns are decoded as INSN_OTHER, objtool considers
that the second function never returns.
If conditional returns are decoded as INSN_RETURN, objtool considers
that code after that conditional return is dead.
To overcome this situation, introduce INSN_RETURN_CONDITIONAL which
is taken as a confirmation that a function is not noreturn but still
sees following code as reachable.
Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
tools/objtool/check.c | 2 +-
tools/objtool/include/objtool/arch.h | 1 +
2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 58d9b1a750e3..10979d68103d 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -279,7 +279,7 @@ static bool __dead_end_function(struct objtool_file *file,
struct symbol *func,
func_for_each_insn(file, func, insn) {
empty = false;
- if (insn->type == INSN_RETURN)
+ if (insn->type == INSN_RETURN || insn->type ==
INSN_RETURN_CONDITIONAL)
return false;
}
diff --git a/tools/objtool/include/objtool/arch.h
b/tools/objtool/include/objtool/arch.h
index d63b46a19f39..900601e2f22b 100644
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -19,6 +19,7 @@ enum insn_type {
INSN_CALL,
INSN_CALL_DYNAMIC,
INSN_RETURN,
+ INSN_RETURN_CONDITIONAL,
INSN_CONTEXT_SWITCH,
INSN_BUG,
INSN_NOP,
--
2.47.0
