cmd/link: put moduledata in its own .go.module section

There is a test for this in CL 721480 later in this series.

For #76038

Change-Id: Ib7ed1f0b0aed2d929ca0f135b54d6b62112cae30
Reviewed-on: https://go-review.googlesource.com/c/go/+/720660
TryBot-Bypass: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>

Author: ianlancetaylor

src/cmd/link/internal/ld/data.go

@@ -1937,6 +1937,26 @@ func (state *dodataState) allocateDataSections(ctxt *Link) {
 	}
 	ldr := ctxt.loader
 
+	// SMODULEDATA needs to be writable, but the GC doesn't need to
+	// look at it. We don't use allocateSingleSymSections because
+	// the name of the section is not the name of the symbol.
+	if len(state.data[sym.SMODULEDATA]) > 0 {
+		if len(state.data[sym.SMODULEDATA]) != 1 {
+			Errorf("internal error: more than one SMODULEDATA symbol")
+		}
+		s := state.data[sym.SMODULEDATA][0]
+		sect := addsection(ldr, ctxt.Arch, &Segdata, ".go.module", 06)
+		sect.Align = symalign(ldr, s)
+		state.datsize = Rnd(state.datsize, int64(sect.Align))
+		sect.Vaddr = uint64(state.datsize)
+		ldr.SetSymSect(s, sect)
+		state.setSymType(s, sym.SDATA)
+		ldr.SetSymValue(s, int64(uint64(state.datsize)-sect.Vaddr))
+		state.datsize += ldr.SymSize(s)
+		sect.Length = uint64(state.datsize) - sect.Vaddr
+		state.checkdatsize(sym.SMODULEDATA)
+	}
+
 	// writable .got (note that for PIE binaries .got goes in relro)
 	if len(state.data[sym.SELFGOT]) > 0 {
 		state.allocateNamedSectionAndAssignSyms(&Segdata, ".got", sym.SELFGOT, sym.SDATA, 06)

src/cmd/link/internal/ld/lib.go

@@ -923,9 +923,7 @@ func (ctxt *Link) linksetup() {
 		mdsb = ctxt.loader.MakeSymbolUpdater(moduledata)
 		ctxt.loader.SetAttrLocal(moduledata, true)
 	}
-	// In all cases way we mark the moduledata as noptrdata to hide it from
-	// the GC.
-	mdsb.SetType(sym.SNOPTRDATA)
+	mdsb.SetType(sym.SMODULEDATA)
 	ctxt.loader.SetAttrReachable(moduledata, true)
 	ctxt.Moduledata = moduledata
 

src/cmd/link/internal/ld/xcoff.go

@@ -1254,7 +1254,7 @@ func Xcoffadddynrel(target *Target, ldr *loader.Loader, syms *ArchSyms, s loader
 					break
 				}
 			}
-		} else if t := ldr.SymType(s); t.IsDATA() || t.IsNOPTRDATA() || t == sym.SBUILDINFO || t == sym.SXCOFFTOC {
+		} else if t := ldr.SymType(s); t.IsDATA() || t.IsNOPTRDATA() || t == sym.SBUILDINFO || t == sym.SXCOFFTOC || t == sym.SMODULEDATA {
 			switch ldr.SymSect(targ).Seg {
 			default:
 				ldr.Errorf(s, "unknown segment for .loader relocation with symbol %s", ldr.SymName(targ))

src/cmd/link/internal/sym/symkind.go

@@ -99,9 +99,10 @@ const (
 	SFIPSINFO           // go:fipsinfo aka crypto/internal/fips140/check.Linkinfo (why is this writable)?
 	SELFSECT            // .got.plt, .plt, .dynamic where appropriate.
 	SMACHO              // Used only for .llvmasm?
-	SMACHOGOT           // Mach-O GOT.
 	SWINDOWS            // Windows dynamic symbols.
+	SMODULEDATA         // Linker generated moduledata struct.
 	SELFGOT             // Writable ELF GOT section.
+	SMACHOGOT           // Mach-O GOT.
 	SNOPTRDATA          // Data with no heap pointers.
 	SNOPTRDATAFIPSSTART // Start of FIPS non-pointer writable data.
 	SNOPTRDATAFIPS      // FIPS non-pointer writable data.

src/cmd/link/internal/sym/symkind_string.go

@@ -127,6 +127,7 @@ func asmb(ctxt *ld.Link, ldr *loader.Loader) {
 		ldr.SymSect(ldr.Lookup("runtime.rodata", 0)),
 		ldr.SymSect(ldr.Lookup("runtime.typelink", 0)),
 		ldr.SymSect(ldr.Lookup("runtime.itablink", 0)),
+		ldr.SymSect(ldr.Lookup("runtime.firstmoduledata", 0)),
 		ldr.SymSect(ldr.Lookup("runtime.pclntab", 0)),
 		ldr.SymSect(ldr.Lookup("runtime.noptrdata", 0)),
 		ldr.SymSect(ldr.Lookup("runtime.data", 0)),