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>

diff --git a/src/cmd/internal/dwarf/dwarf.go b/src/cmd/internal/dwarf/dwarf.go
index 40ec8a6ec29d852460a6eea650046c8a277a2038..6d4e78fb265edfcea6db4a0eec015391a313b34a 100644 (file)
--- 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 886c1ff6725a5699418157635a63779f635f6f20..1dc31c256523fcbf5b0928c562a010d2d081953b 100644 (file)
--- 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)
        }