cmd/link: add variable_parameter attr to functype outparams

When generating DW_TAG_subroutine_type DIEs during linker DWARF type
synthesis, ensure that in the list of children of the subroutine type
DIE (correspondings to input/output params) the output params are
marked with the DW_AT_variable_parameter attribute. In addition, fix
up the generated types of the output params: prior to this patch for a
given output parameter of type T, we would emit the DIE type as *T
(presumably due to how parameter passing/returning worked prior to the
register ABI); with this patch the emitted type will just be T, not *T.

Fixes #59977.

Change-Id: I5b5600be86473695663c75b85baeecad667b9245
Reviewed-on: https://go-review.googlesource.com/c/go/+/595715
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

2 files changed, 30 insertions, 4 deletions

diff --git a/src/cmd/internal/dwarf/dwarf.go b/src/cmd/internal/dwarf/dwarf.go
index 40ec8a6ec2..6d4e78fb26 100644
--- a/src/cmd/internal/dwarf/dwarf.go
+++ b/src/cmd/internal/dwarf/dwarf.go
@@ -338,6 +338,7 @@ const (
 	DW_ABRV_LEXICAL_BLOCK_SIMPLE
 	DW_ABRV_STRUCTFIELD
 	DW_ABRV_FUNCTYPEPARAM
+	DW_ABRV_FUNCTYPEOUTPARAM
 	DW_ABRV_DOTDOTDOT
 	DW_ABRV_ARRAYRANGE
 	DW_ABRV_NULLTYPE
@@ -572,6 +573,8 @@ var abbrevs = []dwAbbrev{
 	{
 		DW_TAG_member,
 		DW_CHILDREN_no,
+		// This abbrev is special-cased by the linker (unlike other DIEs
+		// we don't want a loader.Sym created for this DIE).
 		[]dwAttrForm{
 			{DW_AT_name, DW_FORM_string},
 			{DW_AT_data_member_location, DW_FORM_udata},
@@ -586,15 +589,34 @@ var abbrevs = []dwAbbrev{
 		DW_CHILDREN_no,
 
 		// No name!
+		// This abbrev is special-cased by the linker (unlike other DIEs
+		// we don't want a loader.Sym created for this DIE).
 		[]dwAttrForm{
 			{DW_AT_type, DW_FORM_ref_addr},
 		},
 	},
 
+	/* FUNCTYPEOUTPARAM */
+	{
+		DW_TAG_formal_parameter,
+		DW_CHILDREN_no,
+
+		// No name!
+		// This abbrev is special-cased by the linker (unlike other DIEs
+		// we don't want a loader.Sym created for this DIE).
+		[]dwAttrForm{
+			{DW_AT_variable_parameter, DW_FORM_flag},
+			{DW_AT_type, DW_FORM_ref_addr},
+		},
+	},
+
 	/* DOTDOTDOT */
 	{
 		DW_TAG_unspecified_parameters,
 		DW_CHILDREN_no,
+		// No name.
+		// This abbrev is special-cased by the linker (unlike other DIEs
+		// we don't want a loader.Sym created for this DIE).
 		[]dwAttrForm{},
 	},
 
@@ -604,6 +626,8 @@ var abbrevs = []dwAbbrev{
 		DW_CHILDREN_no,
 
 		// No name!
+		// This abbrev is special-cased by the linker (unlike other DIEs
+		// we don't want a loader.Sym created for this DIE).
 		[]dwAttrForm{
 			{DW_AT_type, DW_FORM_ref_addr},
 			{DW_AT_count, DW_FORM_udata},
diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go
index 886c1ff672..1dc31c2565 100644
--- a/src/cmd/link/internal/ld/dwarf.go
+++ b/src/cmd/link/internal/ld/dwarf.go
@@ -286,7 +286,7 @@ func (d *dwctxt) newdie(parent *dwarf.DWDie, abbrev int, name string) *dwarf.DWD
 
 	var st sym.SymKind
 	switch abbrev {
-	case dwarf.DW_ABRV_FUNCTYPEPARAM, dwarf.DW_ABRV_DOTDOTDOT, dwarf.DW_ABRV_STRUCTFIELD, dwarf.DW_ABRV_ARRAYRANGE:
+	case dwarf.DW_ABRV_FUNCTYPEPARAM, dwarf.DW_ABRV_FUNCTYPEOUTPARAM, dwarf.DW_ABRV_DOTDOTDOT, dwarf.DW_ABRV_STRUCTFIELD, dwarf.DW_ABRV_ARRAYRANGE:
 		// There are no relocations against these dies, and their names
 		// are not unique, so don't create a symbol.
 		return die
@@ -622,8 +622,9 @@ func (d *dwctxt) newtype(gotype loader.Sym) *dwarf.DWDie {
 		for i := 0; i < nfields; i++ {
 			s := decodetypeFuncOutType(d.ldr, d.arch, gotype, &relocs, i)
 			sn := d.ldr.SymName(s)
-			fld := d.newdie(die, dwarf.DW_ABRV_FUNCTYPEPARAM, sn[5:])
-			d.newrefattr(fld, dwarf.DW_AT_type, d.defptrto(d.defgotype(s)))
+			fld := d.newdie(die, dwarf.DW_ABRV_FUNCTYPEOUTPARAM, sn[5:])
+			newattr(fld, dwarf.DW_AT_variable_parameter, dwarf.DW_CLS_FLAG, 1, 0)
+			d.newrefattr(fld, dwarf.DW_AT_type, d.defgotype(s))
 		}
 
 	case abi.Interface:
@@ -2096,7 +2097,8 @@ func (d *dwctxt) dwarfGenerateDebugSyms() {
 	seen := loader.MakeBitmap(d.ldr.NSym())
 	for _, s := range infoSec.syms {
 		if seen.Has(s) {
-			log.Fatalf("symbol %s listed multiple times", d.ldr.SymName(s))
+			log.Fatalf("dwarf symbol %s listed multiple times",
+				d.ldr.SymName(s))
 		}
 		seen.Set(s)
 	}