[llvm] r174479 - Attempt to recover gdb bot after r174445.

David Blaikie dblaikie at gmail.com
Fri Feb 8 15:31:02 PST 2013 

On Fri, Feb 8, 2013 at 3:29 PM, Manman Ren <mren at apple.com> wrote:
>
> On Feb 8, 2013, at 3:21 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>> On Fri, Feb 8, 2013 at 3:14 PM, Manman Ren <mren at apple.com> wrote:
>>>
>>> On Feb 8, 2013, at 11:41 AM, David Blaikie <dblaikie at gmail.com> wrote:
>>>
>>>> On Tue, Feb 5, 2013 at 4:59 PM, Manman Ren <mren at apple.com> wrote:
>>>>> Author: mren
>>>>> Date: Tue Feb  5 18:59:41 2013
>>>>> New Revision: 174479
>>>>>
>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=174479&view=rev
>>>>> Log:
>>>>> Attempt to recover gdb bot after r174445.
>>>>>
>>>>> Failure: undefined symbol 'Lline_table_start0'.
>>>>> Root-cause: we use a symbol subtraction to calculate at_stmt_list, but
>>>>> the line table entries are not dumped in the assembly.
>>>>> Fix: use zero instead of a symbol subtraction for Compile Unit 0.
>>>>
>>>> This seems to not have completely fixed problems of this kind. I
>>>> discovered more breakage in DragonEgg. Any attempt to build with debug
>>>> info in DragonEgg is currently broken due to the original change, even
>>>> after this fix.
>>>>
>>>> You can reproduce this without dragonegg:
>>>>
>>>> $ echo "int main() { }" | clang -x c++ -g -S - -o hello.s && clang hello.s
>>>
>>> This simple example worked for me with source up to r174431.
>>
>> It works for me when I revert r174479 + r174445, fails for me with ToT.
> Works for me without any local change:
> Maybe it is because our ld version.
> I got another email from Duncan, there the version of ld is: GNU ld (GNU Binutils for Debian) 2.20.1-system.20100303

I'm not sure how it'd be an ld version issue - when I look at the
assembly produced by the above command I see a reference to the
.Lline_table_start0 symbol in the debug info & no other mention of it.
Seems pretty clearly something that would not be able to be linked...

does your hello.s from the above command not contain any mention of
line_table_start0?

>
> Thanks,
> Manman
>
>>
>>> With r174479, we are not using line_table_start0 in at_stmt_list, so it should be okay if we don't emit the line table entries in MCAsmStreamer.
>>
>> It's not clear to me - have you tried? So far as I can see, with ToT,
>> that repro fails to link with the aforementioned linker error. Are you
>> not seeing that behavior?
>>
>>> I noticed that using -disable-dot-loc will dump the line table entries.
>>
>> Right - because we emit the line table if we don't emit .loc
>> directives. If we do emit .loc directives then we skip the line table
>> because we figure the linker can figure it out based on the .loc
>> directives.
>>
>> - David
>>
>>>
>>> Thanks,
>>> Manman
>>>
>>>> /tmp/hello-5jpGIX.o:(.debug_info+0x1e): undefined reference to
>>>> `.Lline_table_start0'
>>>>
>>>> Essentially: the assembly code emitted by clang -g is currently
>>>> unusable due to this undefined reference
>>>>
>>>> Eric pointed out that MCAsmStreamer.cpp:1420 - where we don't emit the
>>>> line table if we expect the .loc directives to be sufficient for the
>>>> assembler to create the line table itself. Since we don't emit the
>>>> line table we don't emit the extra special line_table_start symbol
>>>> that's being used in the debug info. (this is paraphrased from Eric's
>>>> comments based on my rather shallow understanding of the issues)
>>>>
>>>> - David
>>>>
>>>>>
>>>>> Modified:
>>>>>   llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
>>>>>   llvm/trunk/test/CodeGen/ARM/2011-01-19-MergedGlobalDbg.ll
>>>>>   llvm/trunk/test/CodeGen/ARM/2011-08-02-MergedGlobalDbg.ll
>>>>>   llvm/trunk/test/CodeGen/X86/2011-01-24-DbgValue-Before-Use.ll
>>>>>   llvm/trunk/test/CodeGen/X86/dbg-value-location.ll
>>>>>   llvm/trunk/test/DebugInfo/X86/stringpool.ll
>>>>>
>>>>> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
>>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp?rev=174479&r1=174478&r2=174479&view=diff
>>>>> ==============================================================================
>>>>> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp (original)
>>>>> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp Tue Feb  5 18:59:41 2013
>>>>> @@ -674,6 +674,8 @@ CompileUnit *DwarfDebug::constructCompil
>>>>>  if (Asm->MAI->doesDwarfUseRelocationsAcrossSections())
>>>>>    NewCU->addLabel(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4,
>>>>>                    LineTableStartSym);
>>>>> +  else if (NewCU->getUniqueID() == 0)
>>>>> +    NewCU->addUInt(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4, 0);
>>>>>  else
>>>>>    NewCU->addDelta(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4,
>>>>>                    LineTableStartSym, Asm->GetTempSymbol("section_line"));
>>>>>
>>>>> Modified: llvm/trunk/test/CodeGen/ARM/2011-01-19-MergedGlobalDbg.ll
>>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/2011-01-19-MergedGlobalDbg.ll?rev=174479&r1=174478&r2=174479&view=diff
>>>>> ==============================================================================
>>>>> --- llvm/trunk/test/CodeGen/ARM/2011-01-19-MergedGlobalDbg.ll (original)
>>>>> +++ llvm/trunk/test/CodeGen/ARM/2011-01-19-MergedGlobalDbg.ll Tue Feb  5 18:59:41 2013
>>>>> @@ -17,7 +17,7 @@ target triple = "thumbv7-apple-darwin10"
>>>>> ; DW_OP_constu
>>>>> ; offset
>>>>>
>>>>> -;CHECK: .long Lset7
>>>>> +;CHECK: .long Lset6
>>>>> ;CHECK-NEXT:        @ DW_AT_type
>>>>> ;CHECK-NEXT:        @ DW_AT_decl_file
>>>>> ;CHECK-NEXT:        @ DW_AT_decl_line
>>>>>
>>>>> Modified: llvm/trunk/test/CodeGen/ARM/2011-08-02-MergedGlobalDbg.ll
>>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/2011-08-02-MergedGlobalDbg.ll?rev=174479&r1=174478&r2=174479&view=diff
>>>>> ==============================================================================
>>>>> --- llvm/trunk/test/CodeGen/ARM/2011-08-02-MergedGlobalDbg.ll (original)
>>>>> +++ llvm/trunk/test/CodeGen/ARM/2011-08-02-MergedGlobalDbg.ll Tue Feb  5 18:59:41 2013
>>>>> @@ -8,7 +8,7 @@
>>>>> ; DW_OP_constu
>>>>> ; offset
>>>>>
>>>>> -;CHECK: .long Lset34
>>>>> +;CHECK: .long Lset33
>>>>> ;CHECK-NEXT:        @ DW_AT_type
>>>>> ;CHECK-NEXT:        @ DW_AT_decl_file
>>>>> ;CHECK-NEXT:        @ DW_AT_decl_line
>>>>>
>>>>> Modified: llvm/trunk/test/CodeGen/X86/2011-01-24-DbgValue-Before-Use.ll
>>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/2011-01-24-DbgValue-Before-Use.ll?rev=174479&r1=174478&r2=174479&view=diff
>>>>> ==============================================================================
>>>>> --- llvm/trunk/test/CodeGen/X86/2011-01-24-DbgValue-Before-Use.ll (original)
>>>>> +++ llvm/trunk/test/CodeGen/X86/2011-01-24-DbgValue-Before-Use.ll Tue Feb  5 18:59:41 2013
>>>>> @@ -4,7 +4,7 @@ target datalayout = "e-p:64:64:64-i1:8:8
>>>>> target triple = "x86_64-apple-darwin10.0.0"
>>>>>
>>>>> ; Check debug info for variable z_s
>>>>> -;CHECK: .long Lset14
>>>>> +;CHECK: .long Lset13
>>>>> ;CHECK-NEXT:  ## DW_AT_decl_file
>>>>> ;CHECK-NEXT:  ## DW_AT_decl_line
>>>>> ;CHECK-NEXT:  ## DW_AT_type
>>>>>
>>>>> Modified: llvm/trunk/test/CodeGen/X86/dbg-value-location.ll
>>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/dbg-value-location.ll?rev=174479&r1=174478&r2=174479&view=diff
>>>>> ==============================================================================
>>>>> --- llvm/trunk/test/CodeGen/X86/dbg-value-location.ll (original)
>>>>> +++ llvm/trunk/test/CodeGen/X86/dbg-value-location.ll Tue Feb  5 18:59:41 2013
>>>>> @@ -4,7 +4,7 @@ target datalayout = "e-p:64:64:64-i1:8:8
>>>>> target triple = "x86_64-apple-darwin10.0.0"
>>>>> ;Radar 8950491
>>>>>
>>>>> -;CHECK: .long Lset6
>>>>> +;CHECK: .long Lset5
>>>>> ;CHECK-NEXT:        ## DW_AT_decl_file
>>>>> ;CHECK-NEXT:        ## DW_AT_decl_line
>>>>> ;CHECK-NEXT:        ## DW_AT_type
>>>>>
>>>>> Modified: llvm/trunk/test/DebugInfo/X86/stringpool.ll
>>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/X86/stringpool.ll?rev=174479&r1=174478&r2=174479&view=diff
>>>>> ==============================================================================
>>>>> --- llvm/trunk/test/DebugInfo/X86/stringpool.ll (original)
>>>>> +++ llvm/trunk/test/DebugInfo/X86/stringpool.ll Tue Feb  5 18:59:41 2013
>>>>> @@ -23,8 +23,8 @@
>>>>> ; LINUX-NEXT: .quad   yyyy
>>>>>
>>>>> ; Verify that we refer to 'yyyy' without a relocation.
>>>>> -; DARWIN: Lset6 = Linfo_string3-Linfo_string          ## DW_AT_name
>>>>> -; DARWIN-NEXT:        .long   Lset6
>>>>> +; DARWIN: Lset5 = Linfo_string3-Linfo_string          ## DW_AT_name
>>>>> +; DARWIN-NEXT:        .long   Lset5
>>>>> ; DARWIN-NEXT:        .long   39                      ## DW_AT_type
>>>>> ; DARWIN-NEXT:        .byte   1                       ## DW_AT_external
>>>>> ; DARWIN-NEXT:        .byte   1                       ## DW_AT_decl_file
>>>>>
>>>>>
>>>>> _______________________________________________
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>>>
>

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