The .text section for the following program (program0.c) changes after toggling the -g flag.
$ cat program0.c
int a, f;
short b, d;
char c[3];
char e[2];
int main() {
d = ({
int g = &e[1] == &c[2];
b;
});
a = a ^ c[2];
for (; f < 2; f++)
a = e[1];
}
$
$ clang-trunk -v
clang version 13.0.0 (https://github.com/llvm/llvm-project.git ab5ac659c81a453a3f58df94f39fe8ba3cd35918)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/cnsun/usr/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$
$ clang-trunk -O2 -flto program0.c ; objdump --disassemble --section=.text > no_g.txt
$ clang-trunk -g -O2 -flto program0.c ; objdump --disassemble --section=.text > g.txt
$ diff no_g.txt g.txt
16,17c16,17
< 401033: 49 c7 c0 a0 11 40 00 mov $0x4011a0,%r8
< 40103a: 48 c7 c1 30 11 40 00 mov $0x401130,%rcx
---
> 401033: 49 c7 c0 b0 11 40 00 mov $0x4011b0,%r8
> 40103a: 48 c7 c1 40 11 40 00 mov $0x401140,%rcx
88,136c88,132
< 401110: 80 3d 15 2f 00 00 00 cmpb $0x0,0x2f15(%rip) # 40402c <f>
< 401117: 75 07 jne 401120 <main+0x10>
< 401119: c6 05 0c 2f 00 00 01 movb $0x1,0x2f0c(%rip) # 40402c <f>
< 401120: 31 c0 xor %eax,%eax
< 401122: c3 retq
< 401123: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
< 40112a: 00 00 00
< 40112d: 0f 1f 00 nopl (%rax)
<
< 0000000000401130 <__libc_csu_init>:
< 401130: f3 0f 1e fa endbr64
< 401134: 41 57 push %r15
< 401136: 4c 8d 3d 13 2d 00 00 lea 0x2d13(%rip),%r15 # 403e50 <__frame_dummy_init_array_entry>
< 40113d: 41 56 push %r14
< 40113f: 49 89 d6 mov %rdx,%r14
< 401142: 41 55 push %r13
< 401144: 49 89 f5 mov %rsi,%r13
< 401147: 41 54 push %r12
< 401149: 41 89 fc mov %edi,%r12d
< 40114c: 55 push %rbp
< 40114d: 48 8d 2d 04 2d 00 00 lea 0x2d04(%rip),%rbp # 403e58 <__do_global_dtors_aux_fini_array_entry>
< 401154: 53 push %rbx
< 401155: 4c 29 fd sub %r15,%rbp
< 401158: 48 83 ec 08 sub $0x8,%rsp
< 40115c: e8 9f fe ff ff callq 401000 <_init>
< 401161: 48 c1 fd 03 sar $0x3,%rbp
< 401165: 74 1f je 401186 <__libc_csu_init+0x56>
< 401167: 31 db xor %ebx,%ebx
< 401169: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
< 401170: 4c 89 f2 mov %r14,%rdx
< 401173: 4c 89 ee mov %r13,%rsi
< 401176: 44 89 e7 mov %r12d,%edi
< 401179: 41 ff 14 df callq *(%r15,%rbx,8)
< 40117d: 48 83 c3 01 add $0x1,%rbx
< 401181: 48 39 dd cmp %rbx,%rbp
< 401184: 75 ea jne 401170 <__libc_csu_init+0x40>
< 401186: 48 83 c4 08 add $0x8,%rsp
< 40118a: 5b pop %rbx
< 40118b: 5d pop %rbp
< 40118c: 41 5c pop %r12
< 40118e: 41 5d pop %r13
< 401190: 41 5e pop %r14
< 401192: 41 5f pop %r15
< 401194: c3 retq
< 401195: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
< 40119c: 00 00 00 00
<
< 00000000004011a0 <__libc_csu_fini>:
< 4011a0: f3 0f 1e fa endbr64
---
> 401110: 0f be 05 16 2f 00 00 movsbl 0x2f16(%rip),%eax # 40402d <c+0x2>
> 401117: 31 05 13 2f 00 00 xor %eax,0x2f13(%rip) # 404030 <a>
> 40111d: 80 3d 10 2f 00 00 00 cmpb $0x0,0x2f10(%rip) # 404034 <f>
> 401124: 75 14 jne 40113a <main+0x2a>
> 401126: 0f be 05 fd 2e 00 00 movsbl 0x2efd(%rip),%eax # 40402a <e+0x1>
> 40112d: 89 05 fd 2e 00 00 mov %eax,0x2efd(%rip) # 404030 <a>
> 401133: c6 05 fa 2e 00 00 01 movb $0x1,0x2efa(%rip) # 404034 <f>
> 40113a: 31 c0 xor %eax,%eax
> 40113c: c3 retq
> 40113d: 0f 1f 00 nopl (%rax)
>
> 0000000000401140 <__libc_csu_init>:
> 401140: f3 0f 1e fa endbr64
> 401144: 41 57 push %r15
> 401146: 4c 8d 3d 03 2d 00 00 lea 0x2d03(%rip),%r15 # 403e50 <__frame_dummy_init_array_entry>
> 40114d: 41 56 push %r14
> 40114f: 49 89 d6 mov %rdx,%r14
> 401152: 41 55 push %r13
> 401154: 49 89 f5 mov %rsi,%r13
> 401157: 41 54 push %r12
> 401159: 41 89 fc mov %edi,%r12d
> 40115c: 55 push %rbp
> 40115d: 48 8d 2d f4 2c 00 00 lea 0x2cf4(%rip),%rbp # 403e58 <__do_global_dtors_aux_fini_array_entry>
> 401164: 53 push %rbx
> 401165: 4c 29 fd sub %r15,%rbp
> 401168: 48 83 ec 08 sub $0x8,%rsp
> 40116c: e8 8f fe ff ff callq 401000 <_init>
> 401171: 48 c1 fd 03 sar $0x3,%rbp
> 401175: 74 1f je 401196 <__libc_csu_init+0x56>
> 401177: 31 db xor %ebx,%ebx
> 401179: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
> 401180: 4c 89 f2 mov %r14,%rdx
> 401183: 4c 89 ee mov %r13,%rsi
> 401186: 44 89 e7 mov %r12d,%edi
> 401189: 41 ff 14 df callq *(%r15,%rbx,8)
> 40118d: 48 83 c3 01 add $0x1,%rbx
> 401191: 48 39 dd cmp %rbx,%rbp
> 401194: 75 ea jne 401180 <__libc_csu_init+0x40>
> 401196: 48 83 c4 08 add $0x8,%rsp
> 40119a: 5b pop %rbx
> 40119b: 5d pop %rbp
> 40119c: 41 5c pop %r12
> 40119e: 41 5d pop %r13
> 4011a0: 41 5e pop %r14
> 4011a2: 41 5f pop %r15
137a134,139
> 4011a5: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> 4011ac: 00 00 00 00
>
> 00000000004011b0 <__libc_csu_fini>:
> 4011b0: f3 0f 1e fa endbr64
> 4011b4: c3 retq
Extended Description
Note: this might be a duplicate of #50454 , but I'm not sure because the programs look different.
The .text section for the following program (program0.c) changes after toggling the -g flag.