dwarf.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package dwarfgen
     6  
     7  import (
     8  	"bytes"
     9  	"flag"
    10  	"fmt"
    11  	"internal/buildcfg"
    12  	"slices"
    13  	"sort"
    14  	"strings"
    15  
    16  	"cmd/compile/internal/base"
    17  	"cmd/compile/internal/ir"
    18  	"cmd/compile/internal/reflectdata"
    19  	"cmd/compile/internal/ssa"
    20  	"cmd/compile/internal/ssagen"
    21  	"cmd/compile/internal/typecheck"
    22  	"cmd/compile/internal/types"
    23  	"cmd/internal/dwarf"
    24  	"cmd/internal/obj"
    25  	"cmd/internal/objabi"
    26  	"cmd/internal/src"
    27  )
    28  
    29  func Info(ctxt *obj.Link, fnsym *obj.LSym, infosym *obj.LSym, curfn obj.Func) (scopes []dwarf.Scope, inlcalls dwarf.InlCalls) {
    30  	fn := curfn.(*ir.Func)
    31  
    32  	if fn.Nname != nil {
    33  		expect := fn.Linksym()
    34  		if fnsym.ABI() == obj.ABI0 {
    35  			expect = fn.LinksymABI(obj.ABI0)
    36  		}
    37  		if fnsym != expect {
    38  			base.Fatalf("unexpected fnsym: %v != %v", fnsym, expect)
    39  		}
    40  	}
    41  
    42  	// Back when there were two different *Funcs for a function, this code
    43  	// was not consistent about whether a particular *Node being processed
    44  	// was an ODCLFUNC or ONAME node. Partly this is because inlined function
    45  	// bodies have no ODCLFUNC node, which was it's own inconsistency.
    46  	// In any event, the handling of the two different nodes for DWARF purposes
    47  	// was subtly different, likely in unintended ways. CL 272253 merged the
    48  	// two nodes' Func fields, so that code sees the same *Func whether it is
    49  	// holding the ODCLFUNC or the ONAME. This resulted in changes in the
    50  	// DWARF output. To preserve the existing DWARF output and leave an
    51  	// intentional change for a future CL, this code does the following when
    52  	// fn.Op == ONAME:
    53  	//
    54  	// 1. Disallow use of createComplexVars in createDwarfVars.
    55  	//    It was not possible to reach that code for an ONAME before,
    56  	//    because the DebugInfo was set only on the ODCLFUNC Func.
    57  	//    Calling into it in the ONAME case causes an index out of bounds panic.
    58  	//
    59  	// 2. Do not populate apdecls. fn.Func.Dcl was in the ODCLFUNC Func,
    60  	//    not the ONAME Func. Populating apdecls for the ONAME case results
    61  	//    in selected being populated after createSimpleVars is called in
    62  	//    createDwarfVars, and then that causes the loop to skip all the entries
    63  	//    in dcl, meaning that the RecordAutoType calls don't happen.
    64  	//
    65  	// These two adjustments keep toolstash -cmp working for now.
    66  	// Deciding the right answer is, as they say, future work.
    67  	//
    68  	// We can tell the difference between the old ODCLFUNC and ONAME
    69  	// cases by looking at the infosym.Name. If it's empty, DebugInfo is
    70  	// being called from (*obj.Link).populateDWARF, which used to use
    71  	// the ODCLFUNC. If it's non-empty (the name will end in $abstract),
    72  	// DebugInfo is being called from (*obj.Link).DwarfAbstractFunc,
    73  	// which used to use the ONAME form.
    74  	isODCLFUNC := infosym.Name == ""
    75  
    76  	var apdecls []*ir.Name
    77  	// Populate decls for fn.
    78  	if isODCLFUNC {
    79  		for _, n := range fn.Dcl {
    80  			if n.Op() != ir.ONAME { // might be OTYPE or OLITERAL
    81  				continue
    82  			}
    83  			switch n.Class {
    84  			case ir.PAUTO:
    85  				if !n.Used() {
    86  					// Text == nil -> generating abstract function
    87  					if fnsym.Func().Text != nil {
    88  						base.Fatalf("debuginfo unused node (AllocFrame should truncate fn.Func.Dcl)")
    89  					}
    90  					continue
    91  				}
    92  			case ir.PPARAM, ir.PPARAMOUT:
    93  			default:
    94  				continue
    95  			}
    96  			if !ssa.IsVarWantedForDebug(n) {
    97  				continue
    98  			}
    99  			apdecls = append(apdecls, n)
   100  			if n.Type().Kind() == types.TSSA {
   101  				// Can happen for TypeInt128 types. This only happens for
   102  				// spill locations, so not a huge deal.
   103  				continue
   104  			}
   105  			fnsym.Func().RecordAutoType(reflectdata.TypeLinksym(n.Type()))
   106  		}
   107  	}
   108  
   109  	var closureVars map[*ir.Name]int64
   110  	if fn.Needctxt() {
   111  		closureVars = make(map[*ir.Name]int64)
   112  		csiter := typecheck.NewClosureStructIter(fn.ClosureVars)
   113  		for {
   114  			n, _, offset := csiter.Next()
   115  			if n == nil {
   116  				break
   117  			}
   118  			closureVars[n] = offset
   119  			if n.Heapaddr != nil {
   120  				closureVars[n.Heapaddr] = offset
   121  			}
   122  		}
   123  	}
   124  
   125  	decls, dwarfVars := createDwarfVars(fnsym, isODCLFUNC, fn, apdecls, closureVars)
   126  
   127  	// For each type referenced by the functions auto vars but not
   128  	// already referenced by a dwarf var, attach an R_USETYPE relocation to
   129  	// the function symbol to insure that the type included in DWARF
   130  	// processing during linking.
   131  	typesyms := []*obj.LSym{}
   132  	for t := range fnsym.Func().Autot {
   133  		typesyms = append(typesyms, t)
   134  	}
   135  	slices.SortFunc(typesyms, func(a, b *obj.LSym) int {
   136  		return strings.Compare(a.Name, b.Name)
   137  	})
   138  	for _, sym := range typesyms {
   139  		infosym.AddRel(ctxt, obj.Reloc{Type: objabi.R_USETYPE, Sym: sym})
   140  	}
   141  	fnsym.Func().Autot = nil
   142  
   143  	var varScopes []ir.ScopeID
   144  	for _, decl := range decls {
   145  		pos := declPos(decl)
   146  		varScopes = append(varScopes, findScope(fn.Marks, pos))
   147  	}
   148  
   149  	scopes = assembleScopes(fnsym, fn, dwarfVars, varScopes)
   150  	if base.Flag.GenDwarfInl > 0 {
   151  		inlcalls = assembleInlines(fnsym, dwarfVars)
   152  	}
   153  	return scopes, inlcalls
   154  }
   155  
   156  func declPos(decl *ir.Name) src.XPos {
   157  	return decl.Canonical().Pos()
   158  }
   159  
   160  // createDwarfVars process fn, returning a list of DWARF variables and the
   161  // Nodes they represent.
   162  func createDwarfVars(fnsym *obj.LSym, complexOK bool, fn *ir.Func, apDecls []*ir.Name, closureVars map[*ir.Name]int64) ([]*ir.Name, []*dwarf.Var) {
   163  	// Collect a raw list of DWARF vars.
   164  	var vars []*dwarf.Var
   165  	var decls []*ir.Name
   166  	var selected ir.NameSet
   167  
   168  	if base.Ctxt.Flag_locationlists && base.Ctxt.Flag_optimize && fn.DebugInfo != nil && complexOK {
   169  		decls, vars, selected = createComplexVars(fnsym, fn, closureVars)
   170  	} else if fn.ABI == obj.ABIInternal && base.Flag.N != 0 && complexOK {
   171  		decls, vars, selected = createABIVars(fnsym, fn, apDecls, closureVars)
   172  	} else {
   173  		decls, vars, selected = createSimpleVars(fnsym, apDecls, closureVars)
   174  	}
   175  	if fn.DebugInfo != nil {
   176  		// Recover zero sized variables eliminated by the stackframe pass
   177  		for _, n := range fn.DebugInfo.(*ssa.FuncDebug).OptDcl {
   178  			if n.Class != ir.PAUTO {
   179  				continue
   180  			}
   181  			types.CalcSize(n.Type())
   182  			if n.Type().Size() == 0 {
   183  				decls = append(decls, n)
   184  				vars = append(vars, createSimpleVar(fnsym, n, closureVars))
   185  				vars[len(vars)-1].StackOffset = 0
   186  				fnsym.Func().RecordAutoType(reflectdata.TypeLinksym(n.Type()))
   187  			}
   188  		}
   189  	}
   190  
   191  	dcl := apDecls
   192  	if fnsym.WasInlined() {
   193  		dcl = preInliningDcls(fnsym)
   194  	} else {
   195  		// The backend's stackframe pass prunes away entries from the
   196  		// fn's Dcl list, including PARAMOUT nodes that correspond to
   197  		// output params passed in registers. Add back in these
   198  		// entries here so that we can process them properly during
   199  		// DWARF-gen. See issue 48573 for more details.
   200  		debugInfo := fn.DebugInfo.(*ssa.FuncDebug)
   201  		for _, n := range debugInfo.RegOutputParams {
   202  			if !ssa.IsVarWantedForDebug(n) {
   203  				continue
   204  			}
   205  			if n.Class != ir.PPARAMOUT || !n.IsOutputParamInRegisters() {
   206  				panic("invalid ir.Name on debugInfo.RegOutputParams list")
   207  			}
   208  			dcl = append(dcl, n)
   209  		}
   210  	}
   211  
   212  	// If optimization is enabled, the list above will typically be
   213  	// missing some of the original pre-optimization variables in the
   214  	// function (they may have been promoted to registers, folded into
   215  	// constants, dead-coded away, etc).  Input arguments not eligible
   216  	// for SSA optimization are also missing.  Here we add back in entries
   217  	// for selected missing vars. Note that the recipe below creates a
   218  	// conservative location. The idea here is that we want to
   219  	// communicate to the user that "yes, there is a variable named X
   220  	// in this function, but no, I don't have enough information to
   221  	// reliably report its contents."
   222  	// For non-SSA-able arguments, however, the correct information
   223  	// is known -- they have a single home on the stack.
   224  	for _, n := range dcl {
   225  		if selected.Has(n) {
   226  			continue
   227  		}
   228  		c := n.Sym().Name[0]
   229  		if c == '.' || n.Type().IsUntyped() {
   230  			continue
   231  		}
   232  		if n.Class == ir.PPARAM && !ssa.CanSSA(n.Type()) {
   233  			// SSA-able args get location lists, and may move in and
   234  			// out of registers, so those are handled elsewhere.
   235  			// Autos and named output params seem to get handled
   236  			// with VARDEF, which creates location lists.
   237  			// Args not of SSA-able type are treated here; they
   238  			// are homed on the stack in a single place for the
   239  			// entire call.
   240  			vars = append(vars, createSimpleVar(fnsym, n, closureVars))
   241  			decls = append(decls, n)
   242  			continue
   243  		}
   244  		typename := dwarf.InfoPrefix + types.TypeSymName(n.Type())
   245  		decls = append(decls, n)
   246  		tag := dwarf.DW_TAG_variable
   247  		isReturnValue := (n.Class == ir.PPARAMOUT)
   248  		if n.Class == ir.PPARAM || n.Class == ir.PPARAMOUT {
   249  			tag = dwarf.DW_TAG_formal_parameter
   250  		}
   251  		if n.Esc() == ir.EscHeap {
   252  			// The variable in question has been promoted to the heap.
   253  			// Its address is in n.Heapaddr.
   254  			// TODO(thanm): generate a better location expression
   255  		}
   256  		inlIndex := 0
   257  		if base.Flag.GenDwarfInl > 1 {
   258  			if n.InlFormal() || n.InlLocal() {
   259  				inlIndex = posInlIndex(n.Pos()) + 1
   260  				if n.InlFormal() {
   261  					tag = dwarf.DW_TAG_formal_parameter
   262  				}
   263  			}
   264  		}
   265  		declpos := base.Ctxt.InnermostPos(n.Pos())
   266  		vars = append(vars, &dwarf.Var{
   267  			Name:          n.Sym().Name,
   268  			IsReturnValue: isReturnValue,
   269  			Tag:           tag,
   270  			WithLoclist:   true,
   271  			StackOffset:   int32(n.FrameOffset()),
   272  			Type:          base.Ctxt.Lookup(typename),
   273  			DeclFile:      declpos.RelFilename(),
   274  			DeclLine:      declpos.RelLine(),
   275  			DeclCol:       declpos.RelCol(),
   276  			InlIndex:      int32(inlIndex),
   277  			ChildIndex:    -1,
   278  			DictIndex:     n.DictIndex,
   279  			ClosureOffset: closureOffset(n, closureVars),
   280  		})
   281  		// Record go type of to insure that it gets emitted by the linker.
   282  		fnsym.Func().RecordAutoType(reflectdata.TypeLinksym(n.Type()))
   283  	}
   284  
   285  	// Sort decls and vars.
   286  	sortDeclsAndVars(fn, decls, vars)
   287  
   288  	return decls, vars
   289  }
   290  
   291  // sortDeclsAndVars sorts the decl and dwarf var lists according to
   292  // parameter declaration order, so as to insure that when a subprogram
   293  // DIE is emitted, its parameter children appear in declaration order.
   294  // Prior to the advent of the register ABI, sorting by frame offset
   295  // would achieve this; with the register we now need to go back to the
   296  // original function signature.
   297  func sortDeclsAndVars(fn *ir.Func, decls []*ir.Name, vars []*dwarf.Var) {
   298  	paramOrder := make(map[*ir.Name]int)
   299  	idx := 1
   300  	for _, f := range fn.Type().RecvParamsResults() {
   301  		if n, ok := f.Nname.(*ir.Name); ok {
   302  			paramOrder[n] = idx
   303  			idx++
   304  		}
   305  	}
   306  	sort.Stable(varsAndDecls{decls, vars, paramOrder})
   307  }
   308  
   309  type varsAndDecls struct {
   310  	decls      []*ir.Name
   311  	vars       []*dwarf.Var
   312  	paramOrder map[*ir.Name]int
   313  }
   314  
   315  func (v varsAndDecls) Len() int {
   316  	return len(v.decls)
   317  }
   318  
   319  func (v varsAndDecls) Less(i, j int) bool {
   320  	nameLT := func(ni, nj *ir.Name) bool {
   321  		oi, foundi := v.paramOrder[ni]
   322  		oj, foundj := v.paramOrder[nj]
   323  		if foundi {
   324  			if foundj {
   325  				return oi < oj
   326  			} else {
   327  				return true
   328  			}
   329  		}
   330  		return false
   331  	}
   332  	return nameLT(v.decls[i], v.decls[j])
   333  }
   334  
   335  func (v varsAndDecls) Swap(i, j int) {
   336  	v.vars[i], v.vars[j] = v.vars[j], v.vars[i]
   337  	v.decls[i], v.decls[j] = v.decls[j], v.decls[i]
   338  }
   339  
   340  // Given a function that was inlined at some point during the
   341  // compilation, return a sorted list of nodes corresponding to the
   342  // autos/locals in that function prior to inlining. If this is a
   343  // function that is not local to the package being compiled, then the
   344  // names of the variables may have been "versioned" to avoid conflicts
   345  // with local vars; disregard this versioning when sorting.
   346  func preInliningDcls(fnsym *obj.LSym) []*ir.Name {
   347  	fn := base.Ctxt.DwFixups.GetPrecursorFunc(fnsym).(*ir.Func)
   348  	var rdcl []*ir.Name
   349  	for _, n := range fn.Inl.Dcl {
   350  		c := n.Sym().Name[0]
   351  		// Avoid reporting "_" parameters, since if there are more than
   352  		// one, it can result in a collision later on, as in #23179.
   353  		if n.Sym().Name == "_" || c == '.' || n.Type().IsUntyped() {
   354  			continue
   355  		}
   356  		rdcl = append(rdcl, n)
   357  	}
   358  	return rdcl
   359  }
   360  
   361  // createSimpleVars creates a DWARF entry for every variable declared in the
   362  // function, claiming that they are permanently on the stack.
   363  func createSimpleVars(fnsym *obj.LSym, apDecls []*ir.Name, closureVars map[*ir.Name]int64) ([]*ir.Name, []*dwarf.Var, ir.NameSet) {
   364  	var vars []*dwarf.Var
   365  	var decls []*ir.Name
   366  	var selected ir.NameSet
   367  	for _, n := range apDecls {
   368  		if ir.IsAutoTmp(n) {
   369  			continue
   370  		}
   371  
   372  		decls = append(decls, n)
   373  		vars = append(vars, createSimpleVar(fnsym, n, closureVars))
   374  		selected.Add(n)
   375  	}
   376  	return decls, vars, selected
   377  }
   378  
   379  func createSimpleVar(fnsym *obj.LSym, n *ir.Name, closureVars map[*ir.Name]int64) *dwarf.Var {
   380  	var tag int
   381  	var offs int64
   382  
   383  	localAutoOffset := func() int64 {
   384  		offs = n.FrameOffset()
   385  		if base.Ctxt.Arch.FixedFrameSize == 0 {
   386  			offs -= int64(types.PtrSize)
   387  		}
   388  		if buildcfg.FramePointerEnabled {
   389  			offs -= int64(types.PtrSize)
   390  		}
   391  		return offs
   392  	}
   393  
   394  	switch n.Class {
   395  	case ir.PAUTO:
   396  		offs = localAutoOffset()
   397  		tag = dwarf.DW_TAG_variable
   398  	case ir.PPARAM, ir.PPARAMOUT:
   399  		tag = dwarf.DW_TAG_formal_parameter
   400  		if n.IsOutputParamInRegisters() {
   401  			offs = localAutoOffset()
   402  		} else {
   403  			offs = n.FrameOffset() + base.Ctxt.Arch.FixedFrameSize
   404  		}
   405  
   406  	default:
   407  		base.Fatalf("createSimpleVar unexpected class %v for node %v", n.Class, n)
   408  	}
   409  
   410  	typename := dwarf.InfoPrefix + types.TypeSymName(n.Type())
   411  	delete(fnsym.Func().Autot, reflectdata.TypeLinksym(n.Type()))
   412  	inlIndex := 0
   413  	if base.Flag.GenDwarfInl > 1 {
   414  		if n.InlFormal() || n.InlLocal() {
   415  			inlIndex = posInlIndex(n.Pos()) + 1
   416  			if n.InlFormal() {
   417  				tag = dwarf.DW_TAG_formal_parameter
   418  			}
   419  		}
   420  	}
   421  	declpos := base.Ctxt.InnermostPos(declPos(n))
   422  	return &dwarf.Var{
   423  		Name:          n.Sym().Name,
   424  		IsReturnValue: n.Class == ir.PPARAMOUT,
   425  		IsInlFormal:   n.InlFormal(),
   426  		Tag:           tag,
   427  		StackOffset:   int32(offs),
   428  		Type:          base.Ctxt.Lookup(typename),
   429  		DeclFile:      declpos.RelFilename(),
   430  		DeclLine:      declpos.RelLine(),
   431  		DeclCol:       declpos.RelCol(),
   432  		InlIndex:      int32(inlIndex),
   433  		ChildIndex:    -1,
   434  		DictIndex:     n.DictIndex,
   435  		ClosureOffset: closureOffset(n, closureVars),
   436  	}
   437  }
   438  
   439  // createABIVars creates DWARF variables for functions in which the
   440  // register ABI is enabled but optimization is turned off. It uses a
   441  // hybrid approach in which register-resident input params are
   442  // captured with location lists, and all other vars use the "simple"
   443  // strategy.
   444  func createABIVars(fnsym *obj.LSym, fn *ir.Func, apDecls []*ir.Name, closureVars map[*ir.Name]int64) ([]*ir.Name, []*dwarf.Var, ir.NameSet) {
   445  
   446  	// Invoke createComplexVars to generate dwarf vars for input parameters
   447  	// that are register-allocated according to the ABI rules.
   448  	decls, vars, selected := createComplexVars(fnsym, fn, closureVars)
   449  
   450  	// Now fill in the remainder of the variables: input parameters
   451  	// that are not register-resident, output parameters, and local
   452  	// variables.
   453  	for _, n := range apDecls {
   454  		if ir.IsAutoTmp(n) {
   455  			continue
   456  		}
   457  		if _, ok := selected[n]; ok {
   458  			// already handled
   459  			continue
   460  		}
   461  
   462  		decls = append(decls, n)
   463  		vars = append(vars, createSimpleVar(fnsym, n, closureVars))
   464  		selected.Add(n)
   465  	}
   466  
   467  	return decls, vars, selected
   468  }
   469  
   470  // createComplexVars creates recomposed DWARF vars with location lists,
   471  // suitable for describing optimized code.
   472  func createComplexVars(fnsym *obj.LSym, fn *ir.Func, closureVars map[*ir.Name]int64) ([]*ir.Name, []*dwarf.Var, ir.NameSet) {
   473  	debugInfo := fn.DebugInfo.(*ssa.FuncDebug)
   474  
   475  	// Produce a DWARF variable entry for each user variable.
   476  	var decls []*ir.Name
   477  	var vars []*dwarf.Var
   478  	var ssaVars ir.NameSet
   479  
   480  	for varID, dvar := range debugInfo.Vars {
   481  		n := dvar
   482  		ssaVars.Add(n)
   483  		for _, slot := range debugInfo.VarSlots[varID] {
   484  			ssaVars.Add(debugInfo.Slots[slot].N)
   485  		}
   486  
   487  		if dvar := createComplexVar(fnsym, fn, ssa.VarID(varID), closureVars); dvar != nil {
   488  			decls = append(decls, n)
   489  			vars = append(vars, dvar)
   490  		}
   491  	}
   492  
   493  	return decls, vars, ssaVars
   494  }
   495  
   496  // createComplexVar builds a single DWARF variable entry and location list.
   497  func createComplexVar(fnsym *obj.LSym, fn *ir.Func, varID ssa.VarID, closureVars map[*ir.Name]int64) *dwarf.Var {
   498  	debug := fn.DebugInfo.(*ssa.FuncDebug)
   499  	n := debug.Vars[varID]
   500  
   501  	var tag int
   502  	switch n.Class {
   503  	case ir.PAUTO:
   504  		tag = dwarf.DW_TAG_variable
   505  	case ir.PPARAM, ir.PPARAMOUT:
   506  		tag = dwarf.DW_TAG_formal_parameter
   507  	default:
   508  		return nil
   509  	}
   510  
   511  	gotype := reflectdata.TypeLinksym(n.Type())
   512  	delete(fnsym.Func().Autot, gotype)
   513  	typename := dwarf.InfoPrefix + gotype.Name[len("type:"):]
   514  	inlIndex := 0
   515  	if base.Flag.GenDwarfInl > 1 {
   516  		if n.InlFormal() || n.InlLocal() {
   517  			inlIndex = posInlIndex(n.Pos()) + 1
   518  			if n.InlFormal() {
   519  				tag = dwarf.DW_TAG_formal_parameter
   520  			}
   521  		}
   522  	}
   523  	declpos := base.Ctxt.InnermostPos(n.Pos())
   524  	dvar := &dwarf.Var{
   525  		Name:          n.Sym().Name,
   526  		IsReturnValue: n.Class == ir.PPARAMOUT,
   527  		IsInlFormal:   n.InlFormal(),
   528  		Tag:           tag,
   529  		WithLoclist:   true,
   530  		Type:          base.Ctxt.Lookup(typename),
   531  		// The stack offset is used as a sorting key, so for decomposed
   532  		// variables just give it the first one. It's not used otherwise.
   533  		// This won't work well if the first slot hasn't been assigned a stack
   534  		// location, but it's not obvious how to do better.
   535  		StackOffset:   ssagen.StackOffset(debug.Slots[debug.VarSlots[varID][0]]),
   536  		DeclFile:      declpos.RelFilename(),
   537  		DeclLine:      declpos.RelLine(),
   538  		DeclCol:       declpos.RelCol(),
   539  		InlIndex:      int32(inlIndex),
   540  		ChildIndex:    -1,
   541  		DictIndex:     n.DictIndex,
   542  		ClosureOffset: closureOffset(n, closureVars),
   543  	}
   544  	list := debug.LocationLists[varID]
   545  	if len(list) != 0 {
   546  		dvar.PutLocationList = func(listSym, startPC dwarf.Sym) {
   547  			debug.PutLocationList(list, base.Ctxt, listSym.(*obj.LSym), startPC.(*obj.LSym))
   548  		}
   549  	}
   550  	return dvar
   551  }
   552  
   553  // RecordFlags records the specified command-line flags to be placed
   554  // in the DWARF info.
   555  func RecordFlags(flags ...string) {
   556  	if base.Ctxt.Pkgpath == "" {
   557  		panic("missing pkgpath")
   558  	}
   559  
   560  	type BoolFlag interface {
   561  		IsBoolFlag() bool
   562  	}
   563  	type CountFlag interface {
   564  		IsCountFlag() bool
   565  	}
   566  	var cmd bytes.Buffer
   567  	for _, name := range flags {
   568  		f := flag.Lookup(name)
   569  		if f == nil {
   570  			continue
   571  		}
   572  		getter := f.Value.(flag.Getter)
   573  		if getter.String() == f.DefValue {
   574  			// Flag has default value, so omit it.
   575  			continue
   576  		}
   577  		if bf, ok := f.Value.(BoolFlag); ok && bf.IsBoolFlag() {
   578  			val, ok := getter.Get().(bool)
   579  			if ok && val {
   580  				fmt.Fprintf(&cmd, " -%s", f.Name)
   581  				continue
   582  			}
   583  		}
   584  		if cf, ok := f.Value.(CountFlag); ok && cf.IsCountFlag() {
   585  			val, ok := getter.Get().(int)
   586  			if ok && val == 1 {
   587  				fmt.Fprintf(&cmd, " -%s", f.Name)
   588  				continue
   589  			}
   590  		}
   591  		fmt.Fprintf(&cmd, " -%s=%v", f.Name, getter.Get())
   592  	}
   593  
   594  	// Adds flag to producer string signaling whether regabi is turned on or
   595  	// off.
   596  	// Once regabi is turned on across the board and the relative GOEXPERIMENT
   597  	// knobs no longer exist this code should be removed.
   598  	if buildcfg.Experiment.RegabiArgs {
   599  		cmd.Write([]byte(" regabi"))
   600  	}
   601  
   602  	if cmd.Len() == 0 {
   603  		return
   604  	}
   605  	s := base.Ctxt.Lookup(dwarf.CUInfoPrefix + "producer." + base.Ctxt.Pkgpath)
   606  	s.Type = objabi.SDWARFCUINFO
   607  	// Sometimes (for example when building tests) we can link
   608  	// together two package main archives. So allow dups.
   609  	s.Set(obj.AttrDuplicateOK, true)
   610  	base.Ctxt.Data = append(base.Ctxt.Data, s)
   611  	s.P = cmd.Bytes()[1:]
   612  }
   613  
   614  // RecordPackageName records the name of the package being
   615  // compiled, so that the linker can save it in the compile unit's DIE.
   616  func RecordPackageName() {
   617  	s := base.Ctxt.Lookup(dwarf.CUInfoPrefix + "packagename." + base.Ctxt.Pkgpath)
   618  	s.Type = objabi.SDWARFCUINFO
   619  	// Sometimes (for example when building tests) we can link
   620  	// together two package main archives. So allow dups.
   621  	s.Set(obj.AttrDuplicateOK, true)
   622  	base.Ctxt.Data = append(base.Ctxt.Data, s)
   623  	s.P = []byte(types.LocalPkg.Name)
   624  }
   625  
   626  func closureOffset(n *ir.Name, closureVars map[*ir.Name]int64) int64 {
   627  	return closureVars[n]
   628  }
   629
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