| Issue |
125770
|
| Summary |
Differences in LLDB and GDB Behavior When Stepping Into Inline Functions Twice
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
edumoot
|
We found that:
- When debugging a binary compiled with -O3, -O2, or -O1, GDB only steps into the first instance of an inline function, while LLDB steps in twice.
- Additionally, GDB halts at line 25 and LLDB at line 26, even though neither line appears in the debug line table.
Steps to Reproduce:
1. Compile and debug the binary in LLVM 19.1.7 context.
```
$clang -g -O3 6.c -o 6_O3.out
$lldb
(lldb) file 6_O3.out
(lldb) b main
(lldb) r
* thread #1, name = '6_O3.out', stop reason = breakpoint 1.1
frame #0: 0x0000555555555130 6_O3.out`main [inlined] compute_result at 6.c:19:16
16 int32_t secondary_var = -9L;
17
18 global_counter = local_values[7];
-> 19 temp_var = global_array[1] % 0xFCL;
20 secondary_var &= (temp_var | (++global_value));
21 return global_union;
22 }
(lldb) s
* thread #1, name = '6_O3.out', stop reason = step in
frame #0: 0x0000555555555136 6_O3.out`main at 6.c:26:19
23
24 int main(void) {
25 int result0 = compute_result().f0;
-> 26 int result1 = compute_result().f1;
27 global_union.f0++;
28 return result0 == result1;
29 }
(lldb) s
* thread #1, name = '6_O3.out', stop reason = step in
frame #0: 0x0000555555555136 6_O3.out`main [inlined] compute_result at 6.c:19:16
16 int32_t secondary_var = -9L;
17
18 global_counter = local_values[7];
-> 19 temp_var = global_array[1] % 0xFCL;
20 secondary_var &= (temp_var | (++global_value));
21 return global_union;
22 }
(lldb) s
* thread #1, name = '6_O3.out', stop reason = step in
frame #0: 0x000055555555513c 6_O3.out`main [inlined] compute_result at 6.c:20:35
17
18 global_counter = local_values[7];
19 temp_var = global_array[1] % 0xFCL;
-> 20 secondary_var &= (temp_var | (++global_value));
21 return global_union;
22 }
23
(lldb) s
* thread #1, name = '6_O3.out', stop reason = step in
frame #0: 0x0000555555555136 6_O3.out`main at 6.c:26:19
23
24 int main(void) {
25 int result0 = compute_result().f0;
-> 26 int result1 = compute_result().f1;
27 global_union.f0++;
28 return result0 == result1;
29 }
```
2. Debug the binary using GDB 15.
```
$ gdb
GNU gdb (Ubuntu 15.0.50.20240403-0ubuntu1) 15.0.50.20240403-git
Copyright (C) 2024 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
(gdb) file 6_O3.out
(gdb) b main
(gdb) r
[...]
Breakpoint 1, main () at 6.c:25
25 int result0 = compute_result().f0;
(gdb) s
compute_result () at 6.c:19
19 temp_var = global_array[1] % 0xFCL;
(gdb) s
compute_result () at 6.c:20
20 secondary_var &= (temp_var | (++global_value));
(gdb) s
main () at 6.c:27
27 global_union.f0++;
(gdb) s
28 return result0 == result1;
```
3. cat 6.c
```
File: 6.c
01: #include <stdint.h>
02:
03: union U1 {
04: int8_t f0;
05: const int8_t f1;
06: };
07:
08: static uint16_t global_counter = 1UL;
09: static volatile uint32_t global_array[10] = {0UL};
10: static uint32_t global_value = 4294967286UL;
11: static union U1 global_union = {-2L};
12:
13: static union U1 compute_result(void) {
14: int8_t local_values[8] = {0xA0L};
15: int32_t temp_var = 0x5BF2D3F5L;
16: int32_t secondary_var = -9L;
17:
18: global_counter = local_values[7];
19: temp_var = global_array[1] % 0xFCL;
20: secondary_var &= (temp_var | (++global_value));
21: return global_union;
22: }
23:
24: int main(void) {
25: int result0 = compute_result().f0;
26: int result1 = compute_result().f1;
27: global_union.f0++;
28: return result0 == result1;
29: }
30:
```
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