runtime, cmd/link: store type descriptor length, not end

Storing the type descriptor length lets us save a relocation.
It also avoids a problem for Darwin dynamic linking.

For #6853
Fixes #77350

Change-Id: If5c94330fe10d75690325f3d0b0658060ef3eb2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/739681
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

3 files changed, 20 insertions, 16 deletions

diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index 51163c2c8b..682ae267bf 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -1535,10 +1535,6 @@ func fixZeroSizedSymbols(ctxt *Link) {
 	types.SetSize(8)
 	ldr.SetAttrSpecial(types.Sym(), false)
 
-	etypedesc := ldr.CreateSymForUpdate("runtime.etypedesc", 0)
-	etypedesc.SetType(sym.STYPE)
-	ldr.SetAttrSpecial(etypedesc.Sym(), false)
-
 	etypes := ldr.CreateSymForUpdate("runtime.etypes", 0)
 	etypes.SetType(sym.STYPE)
 	ldr.SetAttrSpecial(etypes.Sym(), false)
@@ -2218,7 +2214,6 @@ func (state *dodataState) allocateDataSections(ctxt *Link) {
 
 	sect = createRelroSect(".go.type", sym.STYPE)
 	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.types", 0), sect)
-	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.etypedesc", 0), sect)
 	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.etypes", 0), sect)
 
 	sect = createRelroSect(".go.func", sym.SGOFUNC)
@@ -2437,20 +2432,30 @@ func (state *dodataState) dodataSect(ctxt *Link, symn sym.SymKind, syms []loader
 		})
 
 		// Find the end of the typelink descriptors.
-		// The offset starts at 1 to match the increment in
+		// The size starts at 1 to match the increment in
 		// createRelroSect in allocateDataSections.
 		// TODO: This wastes some space.
-		offset := int64(1)
+		typeLinkSize := int64(1)
 		for i := range sl {
 			si := sl[i].sym
+			if si == head {
+				continue
+			}
 			if _, isTypelink := typelinkStrings[si]; !isTypelink {
 				break
 			}
-			offset = Rnd(offset, int64(symalign(ldr, si)))
-			offset += sl[i].sz
+			typeLinkSize = Rnd(typeLinkSize, int64(symalign(ldr, si)))
+			typeLinkSize += sl[i].sz
 		}
 
-		ldr.SetSymValue(ldr.LookupOrCreateSym("runtime.etypedesc", 0), offset)
+		// Store the length of the typelink descriptors
+		// in the typedesclen field of moduledata.
+		if ctxt.moduledataTypeDescOffset == 0 {
+			Errorf("internal error: phase error: moduledataTypeDescOffset not set in dodataSect")
+		} else {
+			su := ldr.MakeSymbolUpdater(ctxt.Moduledata)
+			su.SetUint(ctxt.Arch, ctxt.moduledataTypeDescOffset, uint64(typeLinkSize))
+		}
 
 	default:
 		sort.Slice(sl, sortFn)
@@ -3098,12 +3103,9 @@ func (ctxt *Link) address() []*sym.Segment {
 	ctxt.xdefine("runtime.rodata", sym.SRODATA, int64(rodata.Vaddr))
 	ctxt.xdefine("runtime.erodata", sym.SRODATA, int64(rodata.Vaddr+rodata.Length))
 	ctxt.xdefine("runtime.types", sym.SRODATA, int64(types.Vaddr))
-	// etypedesc was set to the offset from the symbol start in dodataSect.
-	s := ldr.Lookup("runtime.etypedesc", 0)
-	ctxt.xdefine("runtime.etypedesc", sym.SRODATA, int64(types.Vaddr+uint64(ldr.SymValue(s))))
 	ctxt.xdefine("runtime.etypes", sym.SRODATA, int64(types.Vaddr+types.Length))
 
-	s = ldr.Lookup("runtime.gcdata", 0)
+	s := ldr.Lookup("runtime.gcdata", 0)
 	ldr.SetAttrLocal(s, true)
 	ctxt.xdefine("runtime.egcdata", sym.SRODATA, ldr.SymAddr(s)+ldr.SymSize(s))
 	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.egcdata", 0), ldr.SymSect(s))
diff --git a/src/cmd/link/internal/ld/link.go b/src/cmd/link/internal/ld/link.go
index 2276d39d88..aa4f655cc9 100644
--- a/src/cmd/link/internal/ld/link.go
+++ b/src/cmd/link/internal/ld/link.go
@@ -96,6 +96,8 @@ type Link struct {
 	Textp        []loader.Sym
 	Moduledata   loader.Sym
 
+	moduledataTypeDescOffset int64
+
 	PackageFile  map[string]string
 	PackageShlib map[string]string
 
diff --git a/src/cmd/link/internal/ld/symtab.go b/src/cmd/link/internal/ld/symtab.go
index d63a96d12b..142fb15785 100644
--- a/src/cmd/link/internal/ld/symtab.go
+++ b/src/cmd/link/internal/ld/symtab.go
@@ -433,7 +433,6 @@ func (ctxt *Link) symtab(pcln *pclntab) []sym.SymKind {
 	ctxt.xdefine("runtime.rodata", sym.SRODATA, 0)
 	ctxt.xdefine("runtime.erodata", sym.SRODATAEND, 0)
 	ctxt.xdefine("runtime.types", sym.SRODATA, 0)
-	ctxt.xdefine("runtime.etypedesc", sym.SRODATA, 0)
 	ctxt.xdefine("runtime.etypes", sym.SRODATA, 0)
 	ctxt.xdefine("runtime.noptrdata", sym.SNOPTRDATA, 0)
 	ctxt.xdefine("runtime.enoptrdata", sym.SNOPTRDATAEND, 0)
@@ -619,7 +618,8 @@ func (ctxt *Link) symtab(pcln *pclntab) []sym.SymKind {
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.gcdata", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.gcbss", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.types", 0))
-	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.etypedesc", 0))
+	ctxt.moduledataTypeDescOffset = moduledata.Size()
+	moduledata.AddUint(ctxt.Arch, 0) // filled in by dodataSect
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.etypes", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.rodata", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("go:func.*", 0))