[AArch64] DW_TAG_label prevents elf from loading in Trace32 and other tools
David Blaikie
dblaikie at gmail.com
Thu Aug 28 08:11:12 PDT 2014
On Aug 28, 2014 6:38 AM, "Keith Walker" <kwalker at arm.com> wrote:
>
> 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).
Sorry I didn't notice that in the original dump but that does sound
particularly bogus. I will see if I can reproduce it when I get to the
office.
>
> 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
> > >>
> > >
> >
> >
> > _______________________________________________
> > llvm-commits mailing list
> > llvm-commits at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
>
>
>
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