Well, it seems that there is something wrong with g++ compiler.
I add **return 0** in the end of function `sha_256()`, and the compiled result
is
```
...
36b3: e8 48 fc ff ff callq 3300 <calc_sha256>
36b8: 85 c0 test %eax,%eax
36ba: 75 74 jne 3730 <_Z7sha_256v+0xf0>
...
36c0: 85 ff test %edi,%edi
36c2: 75 60 jne 3724 <_Z7sha_256v+0xe4>
...
3719: 31 c0 xor %eax,%eax
371b: 48 83 c4 10 add $0x10,%rsp
371f: 5b pop %rbx
3720: 5d pop %rbp
3721: 41 5c pop %r12
3723: c3 retq
```
Seems right and the function will return successfully.
On the contrary, if I **DO NOT** add `return 0` ,the compiled result will be
```
...
36b3: e8 48 fc ff ff callq 3300 <calc_sha256>
36b8: 85 c0 test %eax,%eax
36ba: 75 24 jne 36e0 <_Z7sha_256v+0xa0>
36bc: 8b 7c 24 0c mov 0xc(%rsp),%edi
36c0: 85 ff test %edi,%edi
36c2: 74 31 je 36f5 <_Z7sha_256v+0xb5>
...
36f5: 48 8d 35 66 29 00 00 lea 0x2966(%rip),%rsi # 6062
<_IO_stdin_used+0x62>
36fc: bf 01 00 00 00 mov $0x1,%edi
3701: 4c 8d 63 20 lea 0x20(%rbx),%r12
3705: 31 c0 xor %eax,%eax
3707: e8 a4 f0 ff ff callq 27b0 <__printf_chk@plt>
370c: 48 8d 2d 65 29 00 00 lea 0x2965(%rip),%rbp # 6078
<_IO_stdin_used+0x78>
3713: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
3718: 0f b6 13 movzbl (%rbx),%edx
371b: 48 89 ee mov %rbp,%rsi
371e: bf 01 00 00 00 mov $0x1,%edi
3723: 31 c0 xor %eax,%eax
3725: 48 83 c3 01 add $0x1,%rbx
3729: e8 82 f0 ff ff callq 27b0 <__printf_chk@plt>
372e: 4c 39 e3 cmp %r12,%rbx
3731: 75 e5 jne 3718 <_Z7sha_256v+0xd8>
3733: bf 0a 00 00 00 mov $0xa,%edi
3738: e8 63 ed ff ff callq 24a0 <putchar@plt>
373d: 48 8d 3d 39 29 00 00 lea 0x2939(%rip),%rdi # 607d
<_IO_stdin_used+0x7d>
3744: e8 c7 ed ff ff callq 2510 <puts@plt>
3749: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
0000000000003750 <_Z11aes_gcm_128v>:
3750: f3 0f 1e fa endbr64
```
Don't care about address 0x36f5 - 0x3744. They are contents from original file
```
printf("[+] SHA256 result is ");
int i;
for(i = 0; i < 32; i ++) {
printf("%02x", output_hash[i]);
}
printf("\n");
printf("[+] calc_sha256 success ...\n");
```
And we can see address 0x3749, we want the function returns but actually the
machine code doesn't do such thing. So the program will continue executing from
0x3740, which is the start address of function `aes_gcm_128()`. So we can see a
printf result and segmentation fault, which is caused by an unalloced stack
storage for
```
uint8_t aes_gcm_plaintext[16]
```
Maybe it's something wrong with the g++ compiler?
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