runtime, cmd/internal/ld: initialize themoduledata slices directly

This CL is quite conservative in some ways.  It continues to define
symbols that have no real purpose (e.g. epclntab).  These could be
deleted if there is no concern that external tools might look for them.

It would also now be possible to make some changes to the pcln data but
I get the impression that would definitely require some thought and
discussion.

Change-Id: Ib33cde07e4ec38ecc1d6c319a10138c9347933a3
Reviewed-on: https://go-review.googlesource.com/7616
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/proc1.go

@@ -51,7 +51,7 @@ func schedinit() {
 	framepointer_enabled = haveexperiment("framepointer")
 
 	tracebackinit()
-	symtabinit()
+	symtabverify()
 	stackinit()
 	mallocinit()
 	mcommoninit(_g_.m)

src/runtime/runtime1.go

@@ -427,12 +427,7 @@ func gomcache() *mcache {
 //go:linkname reflect_typelinks reflect.typelinks
 //go:nosplit
 func reflect_typelinks() []*_type {
-	var ret []*_type
-	sp := (*slice)(unsafe.Pointer(&ret))
-	sp.array = (*byte)(unsafe.Pointer(themoduledata.typelink))
-	sp.len = uint((themoduledata.etypelink - themoduledata.typelink) / unsafe.Sizeof(ret[0]))
-	sp.cap = sp.len
-	return ret
+	return themoduledata.typelinks
 }
 
 // TODO: move back into mgc.go

src/runtime/symtab.go

@@ -33,11 +33,11 @@ const (
 // image. It is written by the linker. Any changes here must be
 // matched changes to the code in cmd/internal/ld/symtab.go:symtab.
 type moduledata struct {
-	pclntable                      []byte
-	ftab                           []functab
-	filetab                        []uint32
-	pclntab, epclntab, findfunctab uintptr
-	minpc, maxpc                   uintptr
+	pclntable    []byte
+	ftab         []functab
+	filetab      []uint32
+	findfunctab  uintptr
+	minpc, maxpc uintptr
 
 	text, etext           uintptr
 	noptrdata, enoptrdata uintptr
@@ -46,7 +46,7 @@ type moduledata struct {
 	noptrbss, enoptrbss   uintptr
 	end, gcdata, gcbss    uintptr
 
-	typelink, etypelink uintptr
+	typelinks []*_type
 }
 
 var themoduledata moduledata // linker symbol
@@ -72,30 +72,19 @@ type findfuncbucket struct {
 	subbuckets [16]byte
 }
 
-func symtabinit() {
+func symtabverify() {
 	// See golang.org/s/go12symtab for header: 0xfffffffb,
 	// two zero bytes, a byte giving the PC quantum,
 	// and a byte giving the pointer width in bytes.
-	pcln := (*[8]byte)(unsafe.Pointer(themoduledata.pclntab))
-	pcln32 := (*[2]uint32)(unsafe.Pointer(themoduledata.pclntab))
+	pcln := *(**[8]byte)(unsafe.Pointer(&themoduledata.pclntable))
+	pcln32 := *(**[2]uint32)(unsafe.Pointer(&themoduledata.pclntable))
 	if pcln32[0] != 0xfffffffb || pcln[4] != 0 || pcln[5] != 0 || pcln[6] != _PCQuantum || pcln[7] != ptrSize {
 		println("runtime: function symbol table header:", hex(pcln32[0]), hex(pcln[4]), hex(pcln[5]), hex(pcln[6]), hex(pcln[7]))
 		throw("invalid function symbol table\n")
 	}
 
-	// pclntable is all bytes of pclntab symbol.
-	sp := (*sliceStruct)(unsafe.Pointer(&themoduledata.pclntable))
-	sp.array = unsafe.Pointer(themoduledata.pclntab)
-	sp.len = int(uintptr(unsafe.Pointer(themoduledata.epclntab)) - uintptr(unsafe.Pointer(themoduledata.pclntab)))
-	sp.cap = sp.len
-
 	// ftab is lookup table for function by program counter.
-	nftab := int(*(*uintptr)(add(unsafe.Pointer(pcln), 8)))
-	p := add(unsafe.Pointer(pcln), 8+ptrSize)
-	sp = (*sliceStruct)(unsafe.Pointer(&themoduledata.ftab))
-	sp.array = p
-	sp.len = nftab + 1
-	sp.cap = sp.len
+	nftab := len(themoduledata.ftab) - 1
 	for i := 0; i < nftab; i++ {
 		// NOTE: ftab[nftab].entry is legal; it is the address beyond the final function.
 		if themoduledata.ftab[i].entry > themoduledata.ftab[i+1].entry {
@@ -113,22 +102,10 @@ func symtabinit() {
 		}
 	}
 
-	// The ftab ends with a half functab consisting only of
-	// 'entry', followed by a uint32 giving the pcln-relative
-	// offset of the file table.
-	sp = (*sliceStruct)(unsafe.Pointer(&themoduledata.filetab))
-	end := unsafe.Pointer(&themoduledata.ftab[nftab].funcoff) // just beyond ftab
-	fileoffset := *(*uint32)(end)
-	sp.array = unsafe.Pointer(&themoduledata.pclntable[fileoffset])
-	// length is in first element of array.
-	// set len to 1 so we can get first element.
-	sp.len = 1
-	sp.cap = 1
-	sp.len = int(themoduledata.filetab[0])
-	sp.cap = sp.len
-
-	themoduledata.minpc = themoduledata.ftab[0].entry
-	themoduledata.maxpc = themoduledata.ftab[nftab].entry
+	if themoduledata.minpc != themoduledata.ftab[0].entry ||
+		themoduledata.maxpc != themoduledata.ftab[nftab].entry {
+		throw("minpc or maxpc invalid")
+	}
 }
 
 // FuncForPC returns a *Func describing the function that contains the