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

Eric Christopher echristo at gmail.com
Mon Feb 3 14:16:30 PST 2014 

On Mon, Feb 3, 2014 at 2:09 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>
>
> On Fri, Feb 8, 2013 at 3:44 PM, Manman Ren <mren at apple.com> wrote:
>>
>>
>> On Feb 8, 2013, at 3:39 PM, David Blaikie <dblaikie at gmail.com> wrote:
>>
>> > On Fri, Feb 8, 2013 at 3:35 PM, Manman Ren <mren at apple.com> wrote:
>> >>
>> >> On Feb 8, 2013, at 3:31 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> >>
>> >>> 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?
>> >> No, my hello.s does not have line_table_start0.
>> >
>> > That bit I find a little surprising - but I'm probably still not
>> > understanding something.
>> >
>> > Eric pointed out on IRC/offline, though, that this probably doesn't
>> > reproduce on Darwin as we unconditionally emit the line table on
>> > Darwin for some reason (perhaps the linker doesn't support the .loc
>> > directives?).
>> >
>> > if you try:
>> >
>> > clang hello.cpp -g -S -target i386-pc-linux-gnu
>> >
>> > you'll see the hello.s file contains a reference to
>> > .Lline_table_start0 but no definition for it - this is a/the problem
>>
>> I see the problem, we are seeing different behavior because of this flag
>> Asm->MAI->doesDwarfUseRelocationsAcrossSections()
>> I will check in a fix soon.
>>
>> Thanks,
>> Manman
>
>
> (it'd be useful to have a follow up reply to this review thread mentioning
> which revision your fix was committed in (and, in the future, to have that
> revision mention the revision it was intended to fix - bidirectional
> association, makes it easier when trying to resurrect the history of
> changes))
>
>>
>> >>>>>>>> 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);
>
>
> And in looking at this actual code... this line seems problematic/wrong.
> Using a constant will never be correct if this debug info is ever linked
> with another object file (because, while it may be a zero offset now, once
> linked it may become non-zero).
>
> I'm still trying to wrap my head around why we have a special case for
> textual output... but I'll see what I can manage/understand with more
> staring.
>

The summary there is that .loc directives don't support multiple
compile units and so if we have multiple compile units, .loc
directives, and textual output into a .s file we can't represent it
very well (read: at all).

-eric

> - David
>
>>
>> >>>>>>>> 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
>> >>>>>>>>
>> >>>>>>>>
>> >>>>>>>> _______________________________________________
>> >>>>>>>> llvm-commits mailing list
>> >>>>>>>> llvm-commits at cs.uiuc.edu
>> >>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>> >>>>>>
>> >>>>
>> >>
>>
>

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