go tool link: 调试信息生成
ld.Main()->dwarfGenerateDebugSyms()
下面是链接器生成所有DWARF调试信息的路径，
file: cmd/link/internal/ld/main.go
func Main() {
...
// entry1: generate dwarf data .debug_info for all types, variables, ...
dwarfGenerateDebugInfo(ctxt)
...
// entry2: generate dwarf data for all other .debug_ sections
dwarfGenerateDebugSyms(ctxt)
...
// compress generated dwarf data
dwarfcompress(ctxt)
...
}
分析一下这两个函数的关系：
- 从代码注释中可以看到这两个函数是 DWARF 调试信息生成的两个主要入口点：
// dwarfGenerateDebugInfo generated debug info entries for all types,
// variables and functions in the program.
// Along with dwarfGenerateDebugSyms they are the two main entry points into
// dwarf generation: dwarfGenerateDebugInfo does all the work that should be
// done before symbol names are mangled while dwarfGenerateDebugSyms does
// all the work that can only be done after addresses have been assigned to
// text symbols.
它们的主要区别在于执行时机和职责：
dwarfGenerateDebugInfo:- 在符号名称被修改(mangled)之前执行 （源代码中的函数
func Add(a, b int) int，经过名称修饰后可能变成go.info.Add$main$int$int$int） - 负责生成所有类型、变量和函数的调试信息条目
- 主要处理 DWARF 信息的内容生成
- 在符号名称被修改(mangled)之前执行 （源代码中的函数
dwarfGenerateDebugSyms:- 在文本符号(text symbols)的地址被分配之后执行
- 负责生成调试符号
- 主要处理 DWARF 信息的布局和最终输出
从
main.go中的调用顺序可以看出它们的执行顺序：
bench.Start("dwarfGenerateDebugInfo")
dwarfGenerateDebugInfo(ctxt)
// ... 中间有其他操作 ...
bench.Start("dwarfGenerateDebugSyms")
dwarfGenerateDebugSyms(ctxt)
具体实现上：
dwarfGenerateDebugInfo主要做：- 初始化 DWARF 上下文
- 生成类型信息
- 处理编译单元
- 收集变量和函数信息
dwarfGenerateDebugSyms主要做：- 生成 .debug_line、.debug_frame 和 .debug_loc 等调试段
- 处理地址相关的信息
- 最终输出调试信息
它们共同完成 DWARF 调试信息的生成，但分成了两个阶段：
- 第一阶段(
dwarfGenerateDebugInfo)专注于内容的生成 - 第二阶段(
dwarfGenerateDebugSyms)专注于布局和输出
- 第一阶段(
这种分阶段的设计使得 DWARF 调试信息的生成更加清晰和可控，同时也符合链接器的工作流程 - 先确定内容，再确定布局和地址。
entry1: dwarfGenerateDebugInfo
// dwarfGenerateDebugInfo generated debug info entries for all types,
// variables and functions in the program.
// Along with dwarfGenerateDebugSyms they are the two main entry points into
// dwarf generation: dwarfGenerateDebugInfo does all the work that should be
// done before symbol names are mangled while dwarfGenerateDebugSyms does
// all the work that can only be done after addresses have been assigned to
// text symbols.
func dwarfGenerateDebugInfo(ctxt *Link) {
...
d := &dwctxt{
linkctxt: ctxt,
ldr: ctxt.loader,
arch: ctxt.Arch,
tmap: make(map[string]loader.Sym),
tdmap: make(map[loader.Sym]loader.Sym),
rtmap: make(map[loader.Sym]loader.Sym),
}
...
// traverse the []*sym.Library
for _, lib := range ctxt.Library {
consts := d.ldr.Lookup(dwarf.ConstInfoPrefix+lib.Pkg, 0)
// traverse the []*sym.CompilationUnit
for _, unit := range lib.Units {
// We drop the constants into the first CU.
if consts != 0 {
unit.Consts = sym.LoaderSym(consts)
d.importInfoSymbol(consts)
consts = 0
}
ctxt.compUnits = append(ctxt.compUnits, unit)
...
newattr(unit.DWInfo, dwarf.DW_AT_comp_dir, dwarf.DW_CLS_STRING, int64(len(compDir)), compDir)
...
newattr(unit.DWInfo, dwarf.DW_AT_go_package_name, dwarf.DW_CLS_STRING, int64(len(pkgname)), pkgname)
...
// Scan all functions in this compilation unit, create
// DIEs for all referenced types, find all referenced
// abstract functions, visit range symbols. Note that
// Textp has been dead-code-eliminated already.
for _, s := range unit.Textp {
d.dwarfVisitFunction(loader.Sym(s), unit)
}
}
}
// Make a pass through all data symbols, looking for those
// corresponding to reachable, Go-generated, user-visible
// global variables. For each global of this sort, locate
// the corresponding compiler-generated DIE symbol and tack
// it onto the list associated with the unit.
// Also looks for dictionary symbols and generates DIE symbols for each
// type they reference.
for idx := loader.Sym(1); idx < loader.Sym(d.ldr.NDef()); idx++ {
if !d.ldr.AttrReachable(idx) ||
d.ldr.AttrNotInSymbolTable(idx) ||
d.ldr.SymVersion(idx) >= sym.SymVerStatic {
continue
}
t := d.ldr.SymType(idx)
switch t {
case sym.SRODATA, sym.SDATA, sym.SNOPTRDATA, sym.STYPE, sym.SBSS, sym.SNOPTRBSS, sym.STLSBSS:
// ok
default:
continue
}
// Skip things with no type, unless it's a dictionary
gt := d.ldr.SymGoType(idx)
if gt == 0 {
if t == sym.SRODATA {
if d.ldr.IsDict(idx) {
// This is a dictionary, make sure that all types referenced by this dictionary are reachable
relocs := d.ldr.Relocs(idx)
for i := 0; i < relocs.Count(); i++ {
reloc := relocs.At(i)
if reloc.Type() == objabi.R_USEIFACE {
d.defgotype(reloc.Sym())
}
}
}
}
continue
}
...
// Find compiler-generated DWARF info sym for global in question,
// and tack it onto the appropriate unit. Note that there are
// circumstances under which we can't find the compiler-generated
// symbol-- this typically happens as a result of compiler options
// (e.g. compile package X with "-dwarf=0").
varDIE := d.ldr.GetVarDwarfAuxSym(idx)
if varDIE != 0 {
unit := d.ldr.SymUnit(idx)
d.defgotype(gt)
unit.VarDIEs = append(unit.VarDIEs, sym.LoaderSym(varDIE))
}
}
d.synthesizestringtypes(ctxt, dwtypes.Child)
d.synthesizeslicetypes(ctxt, dwtypes.Child)
d.synthesizemaptypes(ctxt, dwtypes.Child)
d.synthesizechantypes(ctxt, dwtypes.Child)
}
entry2: dwarfGenerateDebugSyms
// dwarfGenerateDebugSyms constructs debug_line, debug_frame, and
// debug_loc. It also writes out the debug_info section using symbols
// generated in dwarfGenerateDebugInfo2.
func dwarfGenerateDebugSyms(ctxt *Link) {
if !dwarfEnabled(ctxt) {
return
}
d := &dwctxt{
linkctxt: ctxt,
ldr: ctxt.loader,
arch: ctxt.Arch,
dwmu: new(sync.Mutex),
}
d.dwarfGenerateDebugSyms()
}
ld.Main()→dwarfcompress(*Link)
linker对dwarf调试信息进行必要的压缩
// dwarfcompress compresses the DWARF sections. Relocations are applied
// on the fly. After this, dwarfp will contain a different (new) set of
// symbols, and sections may have been replaced.
func dwarfcompress(ctxt *Link) {
...
}