[PATCH v3 0/1] MR6780: include: Avoid the for-loop be optimized out
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(a)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(a)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(a)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(a)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. https://gitlab.winehq.org/wine/wine/-/merge_requests/6780
From: Ruslan Garipov <ruslanngaripov(a)gmail.com> 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 a flexible array of one element **and it is an interior member** of the structure: 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: # this printf(3)'s "File table: ..." 524f: call 4160 <printf(a)plt> # r15 stores sourceFile->cSeg; assigned above. 5254: cmpw $0x0,(%r12) # r12 is sourceFile 525a: je 527e <dump_codeview+0x70e> 525c: lea 0x4(%r12,%r15,4),%rax #rax is seg_info_dw 5261: mov 0x4(%r12),%r8d # sourceFile->baseSrcLn[0] 5266: mov $0x1,%esi 526b: lea 0x402fe(%rip),%rdi # 45570 5272: mov 0x4(%rax),%ecx 5275: mov (%rax),%edx 5277: xor %eax,%eax 5279: call 4160 <printf(a)plt> 527e: 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: # this printf(3)'s "File table: ..." 525c: call 4160 <printf(a)plt> # r12 is seg_info_dw and r15 stores integer 1; both assigned above. # r15 is `i' -- the loop counter. 5261: cmpw $0x0,(%r14) # r14 is sourceFile 5266: je 529f <dump_codeview+0x72f> 5268: nopl 0x0(%rax,%rax,1) 526f: 5270: mov -0x8(%r12,%r15,8),%edx 5275: mov -0x4(%r12,%r15,8),%ecx 527a: mov %r15d,%esi 527d: xor %eax,%eax 527f: mov (%r14,%r15,4),%r8d # sourceFile->baseSrcLn[i] 5283: lea 0x402e6(%rip),%rdi # 45570 528a: add $0x1,%r15 528e: call 4160 <printf(a)plt> 5293: movzwl (%r14),%eax 5297: lea -0x1(%r15),%edx 529b: cmp %eax,%edx 529d: jl 5270 <dump_codeview+0x700> 529f: mov 0x18(%rsp),%rax # rax = sourceModule + ofs The for-loop now is where it should be. Signed-off-by: Ruslan Garipov <ruslanngaripov(a)gmail.com> --- include/wine/mscvpdb.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/wine/mscvpdb.h b/include/wine/mscvpdb.h index d389d5d22d0..684591ee2fe 100644 --- a/include/wine/mscvpdb.h +++ b/include/wine/mscvpdb.h @@ -2779,9 +2779,9 @@ typedef struct OMFSourceFile { unsigned short cSeg; unsigned short reserved; - unsigned int baseSrcLn[1]; - unsigned short cFName; - char Name; + unsigned int baseSrcLn[]; + /* unsigned short cFName; */ + /* char Name; */ } OMFSourceFile; typedef struct OMFSourceModule -- GitLab https://gitlab.winehq.org/wine/wine/-/merge_requests/6780
This merge request was closed by Ruslan Garipov. -- https://gitlab.winehq.org/wine/wine/-/merge_requests/6780
Superseded by 3310434ec67 (include: Fix some invalid array definitions in PDB structures., 2025-02-26). -- https://gitlab.winehq.org/wine/wine/-/merge_requests/6780#note_96092
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Ruslan Garipov (＠ruslangaripov)