https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100464
Bug ID: 100464
Summary: emitted binary code changes when -g is enabled at -O3
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: cnsun at uwaterloo dot ca
Target Milestone: ---
For the following program, when I turn on and off the flag '-g', the emitted
binary code by gcc-trunk is difference.
$ cat small.c
int *a;
static int b, c, d, e, g, h;
int f;
void i() {
int *j[] = {&e, &b, &b, &d, &b, &b, &g, &e, &g, &b, &b,
&b, &b, &g, &e, &e, &b, &b, &d, &b, &b, &e,
&e, &g, &b, &b, &b, &b, &g, &e, &g, &c, &e};
int **k = &j[5];
for (; f;)
b |= *a;
*k = &h;
}
int main() {}
$
$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/scratch/software/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /tmp/tmp.PQ1fNP1RKJ-gcc-builder/gcc/configure
--enable-languages=c,c++,lto --enable-multiarch
--prefix=/scratch/software/gcc-trunk --disable-bootstrap
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210506 (experimental) [master revision
:60f7b28fb:e1fcf14f33e4f371aae8ae497ca58a760d53ca6d] (GCC)
$
$ gcc-trunk small.c -O3 -w ; objdump --disassemble a.out > "no-g.txt"
$ gcc-trunk small.c -O3 -w -g ; objdump --disassemble a.out > "g.txt"
$ diff no-g.txt g.txt
35,36c35,36
< 401043: 49 c7 c0 b0 11 40 00 mov $0x4011b0,%r8
< 40104a: 48 c7 c1 40 11 40 00 mov $0x401140,%rcx
---
> 401043: 49 c7 c0 d0 11 40 00 mov $0x4011d0,%r8
> 40104a: 48 c7 c1 60 11 40 00 mov $0x401160,%rcx
108,156c108,162
< 401128: 74 06 je 401130 <i+0x10>
< 40112a: eb fe jmp 40112a <i+0xa>
< 40112c: 0f 1f 40 00 nopl 0x0(%rax)
< 401130: c3 retq
< 401131: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
< 401138: 00 00 00
< 40113b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
<
< 0000000000401140 <__libc_csu_init>:
< 401140: f3 0f 1e fa endbr64
< 401144: 41 57 push %r15
< 401146: 4c 8d 3d f3 2c 00 00 lea 0x2cf3(%rip),%r15 #
403e40 <__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 e4 2c 00 00 lea 0x2ce4(%rip),%rbp #
403e48 <__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
< 4011a4: c3 retq
< 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
---
> 401128: 74 26 je 401150 <i+0x30>
> 40112a: 48 8b 15 07 2f 00 00 mov 0x2f07(%rip),%rdx #
> 404038 <a>
> 401131: 8b 05 09 2f 00 00 mov 0x2f09(%rip),%eax #
> 404040 <b>
> 401137: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1)
> 40113e: 00 00
> 401140: 0b 02 or (%rdx),%eax
> 401142: 89 05 f8 2e 00 00 mov %eax,0x2ef8(%rip) #
> 404040 <b>
> 401148: eb f6 jmp 401140 <i+0x20>
> 40114a: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1)
> 401150: c3 retq
> 401151: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
> 401158: 00 00 00
> 40115b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
>
> 0000000000401160 <__libc_csu_init>:
> 401160: f3 0f 1e fa endbr64
> 401164: 41 57 push %r15
> 401166: 4c 8d 3d d3 2c 00 00 lea 0x2cd3(%rip),%r15 #
> 403e40 <__frame_dummy_init_array_entry>
> 40116d: 41 56 push %r14
> 40116f: 49 89 d6 mov %rdx,%r14
> 401172: 41 55 push %r13
> 401174: 49 89 f5 mov %rsi,%r13
> 401177: 41 54 push %r12
> 401179: 41 89 fc mov %edi,%r12d
> 40117c: 55 push %rbp
> 40117d: 48 8d 2d c4 2c 00 00 lea 0x2cc4(%rip),%rbp #
> 403e48 <__do_global_dtors_aux_fini_array_entry>
> 401184: 53 push %rbx
> 401185: 4c 29 fd sub %r15,%rbp
> 401188: 48 83 ec 08 sub $0x8,%rsp
> 40118c: e8 6f fe ff ff callq 401000 <_init>
> 401191: 48 c1 fd 03 sar $0x3,%rbp
> 401195: 74 1f je 4011b6 <__libc_csu_init+0x56>
> 401197: 31 db xor %ebx,%ebx
> 401199: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
> 4011a0: 4c 89 f2 mov %r14,%rdx
> 4011a3: 4c 89 ee mov %r13,%rsi
> 4011a6: 44 89 e7 mov %r12d,%edi
> 4011a9: 41 ff 14 df callq *(%r15,%rbx,8)
> 4011ad: 48 83 c3 01 add $0x1,%rbx
> 4011b1: 48 39 dd cmp %rbx,%rbp
> 4011b4: 75 ea jne 4011a0 <__libc_csu_init+0x40>
> 4011b6: 48 83 c4 08 add $0x8,%rsp
> 4011ba: 5b pop %rbx
> 4011bb: 5d pop %rbp
> 4011bc: 41 5c pop %r12
> 4011be: 41 5d pop %r13
> 4011c0: 41 5e pop %r14
> 4011c2: 41 5f pop %r15
> 4011c4: c3 retq
> 4011c5: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> 4011cc: 00 00 00 00
>
> 00000000004011d0 <__libc_csu_fini>:
> 4011d0: f3 0f 1e fa endbr64
> 4011d4: c3 retq
160,164c166,170
< 00000000004011b8 <_fini>:
< 4011b8: f3 0f 1e fa endbr64
< 4011bc: 48 83 ec 08 sub $0x8,%rsp
< 4011c0: 48 83 c4 08 add $0x8,%rsp
< 4011c4: c3 retq
---
> 00000000004011d8 <_fini>:
> 4011d8: f3 0f 1e fa endbr64
> 4011dc: 48 83 ec 08 sub $0x8,%rsp
> 4011e0: 48 83 c4 08 add $0x8,%rsp
> 4011e4: c3 retq
