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

[Ana Pazos]

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).

 

Building the executables with LLVM with no-integrated-as flag works because
GAS does not emit this entry.

 

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)

 

 

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