[llvm-dev] LLD PDB Lines zero number issue

[David Blaikie via llvm-dev]

+rnk who works on COFF debugging things.

 My understanding is that this has nothing to do with the linker - but is a
function of LLVM optimizations creating line zero debug locations. I
believe rnk & folks have disabled line zero emission for CodeView debug
info in some manner - perhaps that needs a flag? or Steven hasn't got a
release with that change in it?

On Thu, Jan 9, 2020 at 4:47 AM Shi, Steven via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hello Rui,
>
> We meet an LLD PDB issue that if we link assembly code with C code and set
> >= -O1 level optimization in LTO, the executable’s PDB will contain wrong
> zero Lines for the assembly code in DEBUG_S_LINES subsection, and then our
> COFF source debuggers will fail to do the source-level debug on the
> executable.  This issue is same in both Linux and Windows, and I figure out
> a simple case in Linux to reproduce this issue as below. Please help to
> give us some advices on how to solve the zero Lines issue.
>
>
>
> $ cat main.c
>
> void assembly_fun();
>
> int main()
>
> {
>
>   int Index1;
>
>   for (Index1 = 0; Index1 == 0; assembly_fun(), Index1++){
>
>     assembly_fun();
>
>   }
>
>   assembly_fun();
>
> }
>
>
>
> $ cat assembly.nasm
>
>     DEFAULT REL
>
>     SECTION .text
>
> global assembly_fun
>
> assembly_fun:
>
>   ret
>
>
>
> $ cat makefile_clanglto_Oz
>
> CC_FLAGS= -g  -m64 -mcmodel=small -target x86_64-unknown-windows
> -gcodeview -flto -Oz
>
> CC =
> /home/jshi19/llvm/clang+llvm-9.0.0-x86_64-linux-gnu-ubuntu-18.04/bin/clang
>
> DLINK_FLAGS = /Machine:X64 /DLL /ENTRY:main /DEBUG:GHASH /lldmap
>
> DLINK =
> /home/jshi19/llvm/clang+llvm-9.0.0-x86_64-linux-gnu-ubuntu-18.04/bin/lld-link
>
> SLINK =
> /home/jshi19/llvm/clang+llvm-9.0.0-x86_64-linux-gnu-ubuntu-18.04/bin/llvm-lib
>
> build:
>
>         "$(CC)" $(CC_FLAGS) -c -o main.obj  main.c
>
>         "nasm" -f win64 -o assembly.obj assembly.nasm
>
>         "$(SLINK)" /OUT:main.lib main.obj
>
>         "$(SLINK)" /OUT:assembly.lib assembly.obj
>
>         "$(DLINK)" /OUT:main.dll $(DLINK_FLAGS) main.lib assembly.lib
>
> clean:
>
>         rm -f *.obj *.lib *.pdb *.dll *.map
>
>
>
> $ make -f makefile_clanglto_Oz
>
> $ llvm-pdbutil dump -l main.pdb
>
>
>
>                            Lines
>
> ============================================================
>
> Mod 0000 | `assembly.obj`:
>
> Mod 0001 | `/home/jshi19/llvm/wrongcode/lld-link5/lto.tmp`:
>
> /home/jshi19/llvm/wrongcode/lld-link5/main.c (MD5:
> 5F82BB79FE2DA0B0549B784CFDC37D05)
>
>   0001:00000004-0000001E, line/addr entries = 5
>
>      3 00000004 !    *0* 00000008 !    5 0000000D !    *0 *00000012 !
> 9 00000017 !
>
>
>
> If we disable the optimization in the CC_FLAGS with -O0 as below, the PDB
> Lines will become correct non-zero numbers.
>
>
>
> CC_FLAGS= -g  -m64 -mcmodel=small -target x86_64-unknown-windows
> -gcodeview -flto -O0
>
> $ llvm-pdbutil dump -l main.pdb
>
>
>
>                            Lines
>
> ============================================================
>
> Mod 0000 | `assembly.obj`:
>
> Mod 0001 | `/home/jshi19/llvm/wrongcode/lld_PDB_issue/lto.tmp`:
>
> /home/jshi19/llvm/wrongcode/lld_PDB_issue/main.c (MD5:
> 5F82BB79FE2DA0B0549B784CFDC37D05)
>
>   0001:00000010-00000050, line/addr entries = 6
>
>      3 00000010 !    5 0000001C !    6 0000002B !    5 00000030 !    8
> 00000042 !    9 00000047 !
>
>
>
>
>
> Thanks
>
> Steven Shi
>
>
>
>
> _______________________________________________
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> llvm-dev at lists.llvm.org
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>
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