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cmd/{compile,link}: relocate generation of DWARF for global vars

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Move DWARF generation for global variables from the linker to the
compiler. This effectively parallelizes this part of DWARF generation,
speeds up the linker minutely, and gives us a slightly more rational
implementation (there was really no compelling reason to do DWARF gen
for globals in the linker).

Change-Id: I0c1c98d3a647258697e90eb91d1d8a9f6f7f376a
Reviewed-on: https://go-review.googlesource.com/c/go/+/295011
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
This commit is contained in:
Than McIntosh 2021-01-07 16:25:41 -05:00
parent 1c9e587b90
commit c819907754
6 changed files with 60 additions and 36 deletions
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2
src/cmd/compile/internal/gc/main.go
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@ -105,7 +105,7 @@ func Main(archInit func(*ssagen.ArchInfo)) {
// Record flags that affect the build result. (And don't
// record flags that don't, since that would cause spurious
// changes in the binary.)
dwarfgen.RecordFlags("B", "N", "l", "msan", "race", "shared", "dynlink", "dwarflocationlists", "dwarfbasentries", "smallframes", "spectre")
dwarfgen.RecordFlags("B", "N", "l", "msan", "race", "shared", "dynlink", "dwarf", "dwarflocationlists", "dwarfbasentries", "smallframes", "spectre")
if !base.EnableTrace && base.Flag.LowerT {
log.Fatalf("compiler not built with support for -t")

1
src/cmd/compile/internal/gc/obj.go
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@ -195,6 +195,7 @@ func dumpGlobal(n *ir.Name) {
}
types.CalcSize(n.Type())
ggloblnod(n)
base.Ctxt.DwarfGlobal(base.Ctxt.Pkgpath, types.TypeSymName(n.Type()), n.Linksym())
}
func dumpGlobalConst(n ir.Node) {

9
src/cmd/internal/dwarf/dwarf.go
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@ -1041,6 +1041,15 @@ func PutIntConst(ctxt Context, info, typ Sym, name string, val int64) {
putattr(ctxt, info, DW_ABRV_INT_CONSTANT, DW_FORM_sdata, DW_CLS_CONSTANT, val, nil)
}
// PutGlobal writes a DIE for a global variable.
func PutGlobal(ctxt Context, info, typ, gvar Sym, name string) {
Uleb128put(ctxt, info, DW_ABRV_VARIABLE)
putattr(ctxt, info, DW_ABRV_VARIABLE, DW_FORM_string, DW_CLS_STRING, int64(len(name)), name)
putattr(ctxt, info, DW_ABRV_VARIABLE, DW_FORM_block1, DW_CLS_ADDRESS, 0, gvar)
putattr(ctxt, info, DW_ABRV_VARIABLE, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, typ)
putattr(ctxt, info, DW_ABRV_VARIABLE, DW_FORM_flag, DW_CLS_FLAG, 1, nil)
}
// PutBasedRanges writes a range table to sym. All addresses in ranges are
// relative to some base address, which must be arranged by the caller
// (e.g., with a DW_AT_low_pc attribute, or in a BASE-prefixed range).

25
src/cmd/internal/obj/dwarf.go
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@ -402,6 +402,31 @@ func (ctxt *Link) DwarfIntConst(myimportpath, name, typename string, val int64)
dwarf.PutIntConst(dwCtxt{ctxt}, s, ctxt.Lookup(dwarf.InfoPrefix+typename), myimportpath+"."+name, val)
}
// DwarfGlobal creates a link symbol containing a DWARF entry for
// a global variable.
func (ctxt *Link) DwarfGlobal(myimportpath, typename string, varSym *LSym) {
if myimportpath == "" || varSym.Local() {
return
}
var varname string
if varSym.Pkg == "_" {
// The frontend uses package "_" to mark symbols that should not
// be referenced by index, e.g. linkname'd symbols.
varname = varSym.Name
} else {
// Convert "".<name> into a fully qualified package.sym name.
varname = objabi.PathToPrefix(myimportpath) + varSym.Name[len(`""`):]
}
dieSymName := dwarf.InfoPrefix + varname
dieSym := ctxt.LookupInit(dieSymName, func(s *LSym) {
s.Type = objabi.SDWARFVAR
s.Set(AttrDuplicateOK, true) // needed for shared linkage
ctxt.Data = append(ctxt.Data, s)
})
typeSym := ctxt.Lookup(dwarf.InfoPrefix + typename)
dwarf.PutGlobal(dwCtxt{ctxt}, dieSym, typeSym, varSym, varname)
}
func (ctxt *Link) DwarfAbstractFunc(curfn interface{}, s *LSym, myimportpath string) {
absfn := ctxt.DwFixups.AbsFuncDwarfSym(s)
if absfn.Size != 0 {

58
src/cmd/link/internal/ld/dwarf.go
View File

@ -458,12 +458,6 @@ func newmemberoffsetattr(die *dwarf.DWDie, offs int32) {
newattr(die, dwarf.DW_AT_data_member_location, dwarf.DW_CLS_CONSTANT, int64(offs), nil)
}
// GDB doesn't like FORM_addr for AT_location, so emit a
// location expression that evals to a const.
func (d *dwctxt) newabslocexprattr(die *dwarf.DWDie, addr int64, symIdx loader.Sym) {
newattr(die, dwarf.DW_AT_location, dwarf.DW_CLS_ADDRESS, addr, dwSym(symIdx))
}
func (d *dwctxt) lookupOrDiag(n string) loader.Sym {
symIdx := d.ldr.Lookup(n, 0)
if symIdx == 0 {
@ -1020,25 +1014,6 @@ func (d *dwctxt) synthesizechantypes(ctxt *Link, die *dwarf.DWDie) {
}
}
func (d *dwctxt) dwarfDefineGlobal(ctxt *Link, symIdx loader.Sym, str string, v int64, gotype loader.Sym) {
// Find a suitable CU DIE to include the global.
// One would think it's as simple as just looking at the unit, but that might
// not have any reachable code. So, we go to the runtime's CU if our unit
// isn't otherwise reachable.
unit := d.ldr.SymUnit(symIdx)
if unit == nil {
unit = ctxt.runtimeCU
}
ver := d.ldr.SymVersion(symIdx)
dv := d.newdie(unit.DWInfo, dwarf.DW_ABRV_VARIABLE, str, int(ver))
d.newabslocexprattr(dv, v, symIdx)
if d.ldr.SymVersion(symIdx) < sym.SymVerStatic {
newattr(dv, dwarf.DW_AT_external, dwarf.DW_CLS_FLAG, 1, 0)
}
dt := d.defgotype(gotype)
d.newrefattr(dv, dwarf.DW_AT_type, dt)
}
// createUnitLength creates the initial length field with value v and update
// offset of unit_length if needed.
func (d *dwctxt) createUnitLength(su *loader.SymbolBuilder, v uint64) {
@ -1552,7 +1527,7 @@ func appendSyms(syms []loader.Sym, src []sym.LoaderSym) []loader.Sym {
func (d *dwctxt) writeUnitInfo(u *sym.CompilationUnit, abbrevsym loader.Sym, infoEpilog loader.Sym) []loader.Sym {
syms := []loader.Sym{}
if len(u.Textp) == 0 && u.DWInfo.Child == nil {
if len(u.Textp) == 0 && u.DWInfo.Child == nil && len(u.VarDIEs) == 0 {
return syms
}
@ -1583,6 +1558,7 @@ func (d *dwctxt) writeUnitInfo(u *sym.CompilationUnit, abbrevsym loader.Sym, inf
if u.Consts != 0 {
cu = append(cu, loader.Sym(u.Consts))
}
cu = appendSyms(cu, u.VarDIEs)
var cusize int64
for _, child := range cu {
cusize += int64(len(d.ldr.Data(child)))
@ -1907,10 +1883,11 @@ func dwarfGenerateDebugInfo(ctxt *Link) {
checkStrictDups = 1
}
// Create DIEs for global variables and the types they use.
// FIXME: ideally this should be done in the compiler, since
// for globals there isn't any abiguity about which package
// a global belongs to.
// 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.
for idx := loader.Sym(1); idx < loader.Sym(d.ldr.NDef()); idx++ {
if !d.ldr.AttrReachable(idx) ||
d.ldr.AttrNotInSymbolTable(idx) ||
@ -1925,7 +1902,8 @@ func dwarfGenerateDebugInfo(ctxt *Link) {
continue
}
// Skip things with no type
if d.ldr.SymGoType(idx) == 0 {
gt := d.ldr.SymGoType(idx)
if gt == 0 {
continue
}
// Skip file local symbols (this includes static tmps, stack
@ -1939,10 +1917,20 @@ func dwarfGenerateDebugInfo(ctxt *Link) {
continue
}
// Create DIE for global.
sv := d.ldr.SymValue(idx)
gt := d.ldr.SymGoType(idx)
d.dwarfDefineGlobal(ctxt, idx, sn, sv, gt)
// 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").
// FIXME: use an aux sym or a relocation here instead of a
// name lookup.
varDIE := d.ldr.Lookup(dwarf.InfoPrefix+sn, 0)
if varDIE != 0 {
unit := d.ldr.SymUnit(idx)
d.defgotype(gt)
unit.VarDIEs = append(unit.VarDIEs, sym.LoaderSym(varDIE))
}
}
d.synthesizestringtypes(ctxt, dwtypes.Child)

1
src/cmd/link/internal/sym/compilation_unit.go
View File

@ -29,6 +29,7 @@ type CompilationUnit struct {
Consts LoaderSym // Package constants DIEs
FuncDIEs []LoaderSym // Function DIE subtrees
VarDIEs []LoaderSym // Global variable DIEs
AbsFnDIEs []LoaderSym // Abstract function DIE subtrees
RangeSyms []LoaderSym // Symbols for debug_range
Textp []LoaderSym // Text symbols in this CU