a.sh:
set -eu
docker run --rm -itv "$PWD:/app" -w /app alpine:3.19 sh -euc '
apk add gcc musl-dev gdb
gcc -g3 a.c
exec sh
'$ sh a.sh
/app # readelf -wi a.out
Contents of the .debug_info section:
...
Compilation Unit @ offset 0x17d:
Length: 0xca (32-bit)
Version: 5
Unit Type: DW_UT_compile (1)
Abbrev Offset: 0xfc
Pointer Size: 8
<0><189>: Abbrev Number: 3 (DW_TAG_compile_unit)
<18a> DW_AT_producer : (indirect string, offset: 0xacf): GNU C17 13.2.1 20231014 -mtune=generic -march=x86-64 -g3
<18e> DW_AT_language : 29 (C11)
<18f> DW_AT_name : (indirect line string, offset: 0x70): a.c
<193> DW_AT_comp_dir : (indirect line string, offset: 0x74): /app
<197> DW_AT_low_pc : 0x1185
<19f> DW_AT_high_pc : 0x29
<1a7> DW_AT_stmt_list : 0xba
<1ab> DW_AT_macros : 0
...
<1><1ee>: Abbrev Number: 2 (DW_TAG_const_type)
<1ef> DW_AT_type : <0x1de>
<1><1f3>: Abbrev Number: 6 (DW_TAG_variable)
<1f4> DW_AT_name : msg
<1f8> DW_AT_decl_file : 1
<1f9> DW_AT_decl_line : 3
<1fa> DW_AT_decl_column : 12
<1fb> DW_AT_type : <0x1ee>
<1ff> DW_AT_external : 1
<1ff> DW_AT_location : 9 byte block: 3 0 20 0 0 0 0 0 0 (DW_OP_addr: 2000)
...
/app # readelf -wm a.out
Contents of the .debug_macro section:
Offset: 0
Version: 5
Offset size: 4
Offset into .debug_line: 0xba
DW_MACRO_import - offset : 0x46
DW_MACRO_start_file - lineno: 0 filenum: 1
DW_MACRO_start_file - lineno: 0 filenum: 3
DW_MACRO_import - offset : 0x980
DW_MACRO_end_file
DW_MACRO_start_file - lineno: 1 filenum: 2
DW_MACRO_define_strp - lineno : 2 macro : _STDIO_H
DW_MACRO_start_file - lineno: 8 filenum: 4
DW_MACRO_import - offset : 0x9a2
DW_MACRO_end_file
DW_MACRO_import - offset : 0x9ca
DW_MACRO_start_file - lineno: 26 filenum: 5
DW_MACRO_import - offset : 0x9f2
DW_MACRO_end_file
DW_MACRO_import - offset : 0xa63
DW_MACRO_end_file
DW_MACRO_define_strp - lineno : 2 macro : MSG "hello world (define)\n"
DW_MACRO_end_file
...
/app # gdb ./a.out
(gdb) b main
Breakpoint 1 at 0x1189: file a.c, line 5.
(gdb) r
Starting program: /app/a.out
Breakpoint 1, main () at a.c:5
5 puts(MSG);
(gdb) p MSG
$1 = "hello world (define)\n"
(gdb) p msg
$2 = "hello world (const)\n"
(gdb) call strcmp(MSG, msg)
$3 = 1
(gdb) call strcmp(msg, MSG)
$4 = -1
(gdb) call strncmp(MSG, msg, 11)
$5 = 0