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熟悉调试数据格式(DWARF)
DWARF 是一种广泛使用的标准化调试数据格式, 是与 ELF 一起设计的, 该名称没有正式的含义, 仅有
"Debugging With Arbitrary Record Formats(使用任意记录格式调试)" 这个非正式含义
编译器产生调试信息(-g)后, 会有一些调试信息加入到可执行文件中, 以 DWARF 为例.
$ objdump -h hello
hello: file format elf64-x86-64
Sections:
Idx Name Size VMA LMA File off Algn
25 .comment 0000001e 0000000000000000 0000000000000000 00003028 2**0
CONTENTS, READONLY
26 .debug_aranges 00000030 0000000000000000 0000000000000000 00003046 2**0
CONTENTS, READONLY, DEBUGGING, OCTETS
27 .debug_info 00000192 0000000000000000 0000000000000000 00003076 2**0
CONTENTS, READONLY, DEBUGGING, OCTETS
28 .debug_abbrev 00000133 0000000000000000 0000000000000000 00003208 2**0
CONTENTS, READONLY, DEBUGGING, OCTETS
29 .debug_line 00000066 0000000000000000 0000000000000000 0000333b 2**0
CONTENTS, READONLY, DEBUGGING, OCTETS
30 .debug_str 000000cf 0000000000000000 0000000000000000 000033a1 2**0
CONTENTS, READONLY, DEBUGGING, OCTETS有这以 debug_ 开头的几个段, 这些就是加入的调试信息了.
还有其他的调试数据格式吗? 有, STABS, 古老的格式, tcc 产生的调试信息就是这个格式的.
如何查看调试信息呢? 有两种手段, gcc vs llvm
$ objdump --dwarf=info hello
hello: file format elf64-x86-64
Contents of the .debug_info section:
Compilation Unit @ offset 0x0:
Length: 0x18e (32-bit)
Version: 4
Abbrev Offset: 0x0
Pointer Size: 8
<2><f2>: Abbrev Number: 7 (DW_TAG_structure_type)
<f3> DW_AT_byte_size : 16
<f4> DW_AT_decl_file : 1
<f5> DW_AT_decl_line : 31
<f6> DW_AT_decl_column : 3
<f7> DW_AT_sibling : <0x10d>
<3><fb>: Abbrev Number: 8 (DW_TAG_member)
<fc> DW_AT_name : d
<fe> DW_AT_decl_file : 1
<ff> DW_AT_decl_line : 32
<100> DW_AT_decl_column : 9
<101> DW_AT_type : <0x58>
<105> DW_AT_data_member_location: 0
<3><106>: Abbrev Number: 13 (DW_TAG_member)
<107> DW_AT_type : <0x10d>
<10b> DW_AT_data_member_location: 8
<3><10c>: Abbrev Number: 0
<2><10d>: Abbrev Number: 14 (DW_TAG_union_type)
<10e> DW_AT_byte_size : 8
<10f> DW_AT_decl_file : 1
<110> DW_AT_decl_line : 33
<111> DW_AT_decl_column : 5
<112> DW_AT_sibling : <0x12d>
<3><116>: Abbrev Number: 15 (DW_TAG_member)
<117> DW_AT_name : l
<119> DW_AT_decl_file : 1
<11a> DW_AT_decl_line : 34
<11b> DW_AT_decl_column : 11
<11c> DW_AT_type : <0x58>
<3><120>: Abbrev Number: 15 (DW_TAG_member)
<121> DW_AT_name : ptr
<125> DW_AT_decl_file : 1
<126> DW_AT_decl_line : 35
<127> DW_AT_decl_column : 12
<128> DW_AT_type : <0x149>$ llvm-dwarfdump hello --debug-info
hello: file format elf64-x86-64
.debug_info contents:
0x00000000: Compile Unit: length = 0x0000018e, format = DWARF32, version = 0x0004, abbr_offset = 0x0000, addr_size = 0x08 (next unit at 0x00000192)
0x000000f2: DW_TAG_structure_type
DW_AT_byte_size (0x10)
DW_AT_decl_file ("/home/iccy/dwarf/src/hello.c")
DW_AT_decl_line (31)
DW_AT_decl_column (0x03)
DW_AT_sibling (0x0000010d)
0x000000fb: DW_TAG_member
DW_AT_name ("d")
DW_AT_decl_file ("/home/iccy/dwarf/src/hello.c")
DW_AT_decl_line (32)
DW_AT_decl_column (0x09)
DW_AT_type (0x00000058 "int")
DW_AT_data_member_location (0x00)
0x00000106: DW_TAG_member
DW_AT_type (0x0000010d "union ")
DW_AT_data_member_location (0x08)
0x0000010c: NULL
0x0000010d: DW_TAG_union_type
DW_AT_byte_size (0x08)
DW_AT_decl_file ("/home/iccy/dwarf/src/hello.c")
DW_AT_decl_line (33)
DW_AT_decl_column (0x05)
DW_AT_sibling (0x0000012d)
0x00000116: DW_TAG_member
DW_AT_name ("l")
DW_AT_decl_file ("/home/iccy/dwarf/src/hello.c")
DW_AT_decl_line (34)
DW_AT_decl_column (0x0b)
DW_AT_type (0x00000058 "int")
0x00000120: DW_TAG_member
DW_AT_name ("ptr")
DW_AT_decl_file ("/home/iccy/dwarf/src/hello.c")
DW_AT_decl_line (35)
DW_AT_decl_column (0x0c)
DW_AT_type (0x00000149 "int *")
该项目签署了 MIT 授权许可, 详情请参阅 LICENSE
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