This stops GCC from optimizing out a `for` loop inside the `dump_cv_sst_src_module()` function, when tools/winedump is compiled with optimization settings -O1 or higher.
Because the `baseSrcLn` field of the `struct OMFSourceFile` was declared as an array of one element **and it is an interior member** of the structure:
```c typedef struct OMFSourceFile { unsigned short cSeg; unsigned short reserved; unsigned int baseSrcLn[1]; unsigned short cFName; char Name; } OMFSourceFile; ```
The compiler/optimizer assumes that the `baseSrcLn` array may have only zero or one element. And generates the corresponding code.
The following shows code that GCC 14.2.1 generates before and after this patch.
Before patch:
``` 524f: e8 0c ef ff ff call 4160 printf@plt # this printf(3)'s "File table: ..." # r15 stores sourceFile->cSeg; assigned above. 5254: 66 41 83 3c 24 00 cmpw $0x0,(%r12) # r12 is sourceFile 525a: 74 22 je 527e <dump_codeview+0x70e> 525c: 4b 8d 44 bc 04 lea 0x4(%r12,%r15,4),%rax #rax is seg_info_dw 5261: 45 8b 44 24 04 mov 0x4(%r12),%r8d # sourceFile->baseSrcLn[0] 5266: be 01 00 00 00 mov $0x1,%esi 526b: 48 8d 3d fe 02 04 00 lea 0x402fe(%rip),%rdi # 45570 5272: 8b 48 04 mov 0x4(%rax),%ecx 5275: 8b 10 mov (%rax),%edx 5277: 31 c0 xor %eax,%eax 5279: e8 e2 ee ff ff call 4160 printf@plt 527e: 41 0f b6 06 movzbl (%r14),%eax # eax = sourceModule + ofs ```
The code checks if the `sourceFile->cSeg` is zero or not, and if not it `printf(3)`s information about the first element in the `baseSrcLn` and first offset pair. There is no `for` loop there, only its first iteration.
After patch:
``` 525c: e8 ff ee ff ff call 4160 printf@plt # this printf(3)'s "File table: ..." # r12 is seg_info_dw and r15 stores integer 1; both assigned above. # r15 is `i' -- the loop counter. 5261: 66 41 83 3e 00 cmpw $0x0,(%r14) # r14 is sourceFile 5266: 74 37 je 529f <dump_codeview+0x72f> 5268: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1) 526f: 00 5270: 43 8b 54 fc f8 mov -0x8(%r12,%r15,8),%edx 5275: 43 8b 4c fc fc mov -0x4(%r12,%r15,8),%ecx 527a: 44 89 fe mov %r15d,%esi 527d: 31 c0 xor %eax,%eax 527f: 47 8b 04 be mov (%r14,%r15,4),%r8d # sourceFile->baseSrcLn[i] 5283: 48 8d 3d e6 02 04 00 lea 0x402e6(%rip),%rdi # 45570 528a: 49 83 c7 01 add $0x1,%r15 528e: e8 cd ee ff ff call 4160 printf@plt 5293: 41 0f b7 06 movzwl (%r14),%eax 5297: 41 8d 57 ff lea -0x1(%r15),%edx 529b: 39 c2 cmp %eax,%edx 529d: 7c d1 jl 5270 <dump_codeview+0x700> 529f: 48 8b 44 24 18 mov 0x18(%rsp),%rax # rax = sourceModule + ofs ```
The `for` loop now is where it should be.
[EDITED] 2025-02-12: Fix merge request title.
-- v3: include: Avoid the for-loop be optimized out.