[llvm-dev] LLD PDB Lines zero number issue

[Reid Kleckner via llvm-dev]

This looks like it was fixed in October:
http://github.com/llvm/llvm-project/commit/9d8f0b3519c4e9e4e2a3d3b19ea0caf9ef3f85ce
See https://llvm.org/PR43530

On Thu, Jan 9, 2020 at 10:01 AM David Blaikie <dblaikie at gmail.com> wrote:

> +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
>>
>>
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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