cmd/internal/obj: minor refactor of wasmimport code

This CL does some minor refactoring of the code handling
wasmimport.
- Put the WasmImport aux reading and writing code together for
  symmetry.
- Define WasmFuncType, embedded in WasmImport. WasmFuncType could
  also be used (later) for wasmexport.
- Move code generation code to a separate function. The containing
  function is already pretty large.
- Simplify linker code a little bit. The loader convention is to
  return the 0 Sym for nonexistent symbol, instead of a separate
  boolean.

No change in generated code. Passes toolstash -cmp
(GOARCH=wasm GOOS=wasip1 go build -toolexec "toolstash -cmp" -a std cmd).

Change-Id: Idc2514f84a08621333841ae4034b81130e0ce411
Reviewed-on: https://go-review.googlesource.com/c/go/+/603135
Reviewed-by: Than McIntosh <thanm@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>

2 files changed, 5 insertions, 63 deletions

diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index f448a3ee7c..98bff775fb 100644
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -1620,21 +1620,11 @@ func (l *Loader) Aux(i Sym, j int) Aux {
 // contains the information necessary for the linker to add a WebAssembly
 // import statement.
 // (https://webassembly.github.io/spec/core/syntax/modules.html#imports)
-func (l *Loader) WasmImportSym(fnSymIdx Sym) (Sym, bool) {
+func (l *Loader) WasmImportSym(fnSymIdx Sym) Sym {
 	if l.SymType(fnSymIdx) != sym.STEXT {
 		log.Fatalf("error: non-function sym %d/%s t=%s passed to WasmImportSym", fnSymIdx, l.SymName(fnSymIdx), l.SymType(fnSymIdx).String())
 	}
-	r, li := l.toLocal(fnSymIdx)
-	auxs := r.Auxs(li)
-	for i := range auxs {
-		a := &auxs[i]
-		switch a.Type() {
-		case goobj.AuxWasmImport:
-			return l.resolve(r, a.Sym()), true
-		}
-	}
-
-	return 0, false
+	return l.aux1(fnSymIdx, goobj.AuxWasmImport)
 }
 
 // SEHUnwindSym returns the auxiliary SEH unwind symbol associated with
diff --git a/src/cmd/link/internal/wasm/asm.go b/src/cmd/link/internal/wasm/asm.go
index 2f511b97c7..09c54c1392 100644
--- a/src/cmd/link/internal/wasm/asm.go
+++ b/src/cmd/link/internal/wasm/asm.go
@@ -12,7 +12,6 @@ import (
 	"cmd/link/internal/ld"
 	"cmd/link/internal/loader"
 	"cmd/link/internal/sym"
-	"encoding/binary"
 	"fmt"
 	"internal/abi"
 	"internal/buildcfg"
@@ -61,55 +60,8 @@ type wasmFuncType struct {
 }
 
 func readWasmImport(ldr *loader.Loader, s loader.Sym) obj.WasmImport {
-	reportError := func(err error) { panic(fmt.Sprintf("failed to read WASM import in sym %v: %v", s, err)) }
-
-	data := ldr.Data(s)
-
-	readUint32 := func() (v uint32) {
-		v = binary.LittleEndian.Uint32(data)
-		data = data[4:]
-		return
-	}
-
-	readUint64 := func() (v uint64) {
-		v = binary.LittleEndian.Uint64(data)
-		data = data[8:]
-		return
-	}
-
-	readByte := func() byte {
-		if len(data) == 0 {
-			reportError(io.EOF)
-		}
-
-		b := data[0]
-		data = data[1:]
-		return b
-	}
-
-	readString := func() string {
-		n := readUint32()
-
-		s := string(data[:n])
-
-		data = data[n:]
-
-		return s
-	}
-
 	var wi obj.WasmImport
-	wi.Module = readString()
-	wi.Name = readString()
-	wi.Params = make([]obj.WasmField, readUint32())
-	for i := range wi.Params {
-		wi.Params[i].Type = obj.WasmFieldType(readByte())
-		wi.Params[i].Offset = int64(readUint64())
-	}
-	wi.Results = make([]obj.WasmField, readUint32())
-	for i := range wi.Results {
-		wi.Results[i].Type = obj.WasmFieldType(readByte())
-		wi.Results[i].Offset = int64(readUint64())
-	}
+	wi.Read(ldr.Data(s))
 	return wi
 }
 
@@ -207,8 +159,8 @@ func asmb2(ctxt *ld.Link, ldr *loader.Loader) {
 		for ri := 0; ri < relocs.Count(); ri++ {
 			r := relocs.At(ri)
 			if r.Type() == objabi.R_WASMIMPORT {
-				if lsym, ok := ldr.WasmImportSym(fn); ok {
-					wi := readWasmImport(ldr, lsym)
+				if wsym := ldr.WasmImportSym(fn); wsym != 0 {
+					wi := readWasmImport(ldr, wsym)
 					hostImportMap[fn] = int64(len(hostImports))
 					hostImports = append(hostImports, &wasmFunc{
 						Module: wi.Module,