[AArch64] DW_TAG_label prevents elf from loading in Trace32 and other tools

[Keith Walker]

Ana,

Did you get any further to the bottom of this issue?

Although the DW_AT_prototyped attribute is not one specified in the DWARF
specification for use on the DW_TAG_label I would have hoped this would be
benign to the tools.

One thing that looks "strange" to me is that the DW_TAG_label has a
DW_TAG_unspecified_parameters as a child.  My suspicion is that the tools do
not expect DW_TAG_label to have any children.  (The DWARF spec is silent is
this respect).

Keith

> -----Original Message-----
> From: llvm-commits-bounces at cs.uiuc.edu [mailto:llvm-commits-
> bounces at cs.uiuc.edu] On Behalf Of Ana Pazos
> Sent: 22 August 2014 22:04
> To: 'David Blaikie'; 'Weiming Zhao'
> Cc: 'llvm-commits'
> Subject: RE: [AArch64] DW_TAG_label prevents elf from loading in
> Trace32 and other tools
> 
> Hi David,
> 
> Unfortunately the tools do not print more details other than a generic
> error message.
> 
> Are you able to load AArch64 executables built with -g on Trace32?
> Maybe you could try to reproduce the issue on your side?
> 
> Thanks,
> Ana.
> 
> -----Original Message-----
> From: David Blaikie [mailto:dblaikie at gmail.com]
> Sent: Friday, August 22, 2014 11:20 AM
> To: Weiming Zhao
> Cc: Ana Pazos; Tim Northover; llvm-commits
> Subject: Re: [AArch64] DW_TAG_label prevents elf from loading in
> Trace32 and other tools
> 
> On Fri, Aug 22, 2014 at 11:18 AM, Weiming Zhao
> <weimingz at codeaurora.org> wrote:
> > Hi David,
> >
> > Thanks for your response.
> > The tool complained that "Entry error near offset xxxx in file yyyy".
> That offset is in .debug_info, around a DIE about asm label.
> 
> I don't think that diagnostic is sufficient for me to guestimate what
> might be the source of the problem, sorry.
> 
> >
> > For C files, clang -g is ok.
> > I just tried C files with labels and it's OK.
> >
> > We do suspect it's an issue of the tool.
> >
> > Thanks,
> > Weiming
> >
> >
> > -----Original Message-----
> > From: David Blaikie [mailto:dblaikie at gmail.com]
> > Sent: Friday, August 22, 2014 10:57 AM
> > To: Ana Pazos
> > Cc: Tim Northover; llvm-commits; weimingz at codeaurora.org
> > Subject: Re: [AArch64] DW_TAG_label prevents elf from loading in
> > Trace32 and other tools
> >
> > On Thu, Aug 21, 2014 at 6:44 PM, Ana Pazos <apazos at codeaurora.org>
> wrote:
> >> Hi Tim,
> >>
> >>
> >>
> >> Trace32 and some other internal tools are not loading AArch64 LLVM
> >> executables built with -g flag and the integrated assembler.
> >>
> >>
> >>
> >> The tools complain about the entry DW_TAG_label in debug_info
> section
> >> emitted for assembly files (code in lib/MC/MCDwarf.cpp).
> >
> > You'd have to be more specific about what those complaints are.
> >
> > So far as I know (and I've looked at a fair bit of debug info - but
> not much of the asm debug info specifically) the DWARF we emit there is
> correct. I could imagine we might have an incorrect relocation for a
> label on a particular architecture or somesuch, but there's not much I
> can do to help diagnose that with the information you've provided.
> >
> >> Building the executables with LLVM with no-integrated-as flag works
> >> because GAS does not emit this entry.
> >
> > Have you tried compiling a piece of C code with an explicit label,
> > using GCC and throwing that at your tools? (clang/LLVM don't produce
> > label debug info for non-asm source, but GCC does - so if it's
> > something to do with the label debug info, that could show it)
> >
> > And/or do your tools work with clang -g output? If it's something
> generically related to relocations/addresses in debug info, I'd imagine
> it would show up with that just as well.
> >
> >>
> >>
> >>
> >> At first I thought setting DW_AT_prototyped to 0 was the issue (it
> >> seems it should be 1 for non-C code). I changed it, but it did not
> help.
> >>
> >>
> >>
> >> The only thing that worked was to not emit DW_TAG_label entries at
> all.
> >>
> >>
> >>
> >> Is this a tool issue or LLVM is not emitting the fields required by
> >> DW_TAG_label correctly?
> >>
> >>
> >>
> >> Thanks for the help,
> >>
> >> Ana.
> >>
> >>
> >>
> >>
> >>
> >> Here is a reduced example:
> >>
> >>
> >>
> >>                 .text
> >>
> >>                 .file        "a.c"
> >>
> >>                 .globl     main
> >>
> >>                 .align     2
> >>
> >>                 .type     main, at function
> >>
> >> main:                                   // @main
> >>
> >> // BB#0:
> >>
> >>                 sub         sp, sp, #16             // =16
> >>
> >>                 movz     w8, #0
> >>
> >>                 str           w8, [sp, #12]
> >>
> >>                 str           w0, [sp, #8]
> >>
> >>                 str           x1, [sp]
> >>
> >>                 ldr           w0, [sp, #8]
> >>
> >>                 add        sp, sp, #16             // =16
> >>
> >>                 ret
> >>
> >> .Ltmp1:
> >>
> >>                 .size       main, .Ltmp1-main
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> aarch64-linux-gnu-objdump -dwarf=info  a.exe
> >>
> >>
> >>
> >> a0.exe:     file format elf64-littleaarch64
> >>
> >>
> >>
> >> Contents of the .debug_info section:
> >>
> >>
> >>
> >>   Compilation Unit @ offset 0x0:
> >>
> >>    Length:        0xa8 (32-bit)
> >>
> >>    Version:       3
> >>
> >>    Abbrev Offset: 0x0
> >>
> >>    Pointer Size:  8
> >>
> >> <0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
> >>
> >>     <c>   DW_AT_stmt_list   : 0x0
> >>
> >>     <10>   DW_AT_low_pc      : 0x400568
> >>
> >>     <18>   DW_AT_high_pc     : 0x400588
> >>
> >>     <20>   DW_AT_name        : a.s
> >>
> >>     <24>   DW_AT_comp_dir    : xxx
> >>
> >>     <6f>   DW_AT_producer    : LLVM ARM
> >>
> >>     <90>   DW_AT_language    : 32769         (MIPS assembler)
> >>
> >> <1><92>: Abbrev Number: 2 (DW_TAG_label)
> >>
> >>     <93>   DW_AT_name        : main
> >>
> >>     <98>   DW_AT_decl_file   : 0x1
> >>
> >>     <9c>   DW_AT_decl_line   : 0x6
> >>
> >>     <a0>   DW_AT_low_pc      : 0x400568
> >>
> >>     <a8>   DW_AT_prototyped  : 0
> >>
> >> <2><a9>: Abbrev Number: 3 (DW_TAG_unspecified_parameters)
> >>
> >> <2><aa>: Abbrev Number: 0
> >>
> >> <1><ab>: Abbrev Number: 0
> >>
> >>
> >>
> >>
> >>
> >> For the executable generated by gcc:
> >>
> >>
> >>
> >> aarch64-linux-gnu-objdump -dwarf=info g.exe
> >>
> >>
> >>
> >> g.exe:     file format elf64-littleaarch64
> >>
> >>
> >>
> >> Contents of the .debug_info section:
> >>
> >>
> >>
> >>   Compilation Unit @ offset 0x0:
> >>
> >>    Length:        0x7b (32-bit)
> >>
> >>    Version:       2
> >>
> >>    Abbrev Offset: 0x0
> >>
> >>    Pointer Size:  8
> >>
> >> <0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
> >>
> >>     <c>   DW_AT_stmt_list   : 0x0
> >>
> >>     <10>   DW_AT_low_pc      : 0x400510
> >>
> >>     <18>   DW_AT_high_pc     : 0x400530
> >>
> >>     <20>   DW_AT_name        : a.s
> >>
> >>     <24>   DW_AT_comp_dir    : xxx
> >>
> >>     <6f>   DW_AT_producer    : GNU AS 2.24.0
> >>
> >>     <7d>   DW_AT_language    : 32769        (MIPS assembler)
> >>
> >>
> >>
> >>
> >>
> >>
> >> _______________________________________________
> >> llvm-commits mailing list
> >> llvm-commits at cs.uiuc.edu
> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> >>
> >
> 
> 
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