cmd/internal/obj/wasm, runtime: detect wasmexport call before runtime initialization

If a wasmexport function is called from the host before
initializing the Go Wasm module, currently it will likely fail
with a bounds error, because the uninitialized SP is 0, and any
SP decrement will make it out of bounds.

As at least some Wasm runtime doesn't call _initialize by default,
This error can be common. And the bounds error looks confusing to
the users. Therefore, we detect this case and emit a clearer error.

Fixes #71240.
Updates #65199.

Change-Id: I107095f08c76cdceb7781ab0304218eab7029ab6
Reviewed-on: https://go-review.googlesource.com/c/go/+/643115
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

src/cmd/internal/obj/wasm/wasmobj.go

@@ -129,6 +129,7 @@ var (
 	morestackNoCtxt       *obj.LSym
 	sigpanic              *obj.LSym
 	wasm_pc_f_loop_export *obj.LSym
+	runtimeNotInitialized *obj.LSym
 )
 
 const (
@@ -149,6 +150,7 @@ func instinit(ctxt *obj.Link) {
 	morestackNoCtxt = ctxt.Lookup("runtime.morestack_noctxt")
 	sigpanic = ctxt.LookupABI("runtime.sigpanic", obj.ABIInternal)
 	wasm_pc_f_loop_export = ctxt.Lookup("wasm_pc_f_loop_export")
+	runtimeNotInitialized = ctxt.Lookup("runtime.notInitialized")
 }
 
 func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
@@ -255,7 +257,7 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 		p = appendp(p, AEnd)
 	}
 
-	if framesize > 0 {
+	if framesize > 0 && s.Func().WasmExport == nil { // genWasmExportWrapper has its own prologue generation
 		p := s.Func().Text
 		p = appendp(p, AGet, regAddr(REG_SP))
 		p = appendp(p, AI32Const, constAddr(framesize))
@@ -935,6 +937,23 @@ func genWasmExportWrapper(s *obj.LSym, appendp func(p *obj.Prog, as obj.As, args
 		panic("wrapper functions for WASM export should not have a body")
 	}
 
+	// Detect and error out if called before runtime initialization
+	// SP is 0 if not initialized
+	p = appendp(p, AGet, regAddr(REG_SP))
+	p = appendp(p, AI32Eqz)
+	p = appendp(p, AIf)
+	p = appendp(p, ACall, obj.Addr{Type: obj.TYPE_MEM, Name: obj.NAME_EXTERN, Sym: runtimeNotInitialized})
+	p = appendp(p, AEnd)
+
+	// Now that we've checked the SP, generate the prologue
+	if framesize > 0 {
+		p = appendp(p, AGet, regAddr(REG_SP))
+		p = appendp(p, AI32Const, constAddr(framesize))
+		p = appendp(p, AI32Sub)
+		p = appendp(p, ASet, regAddr(REG_SP))
+		p.Spadj = int32(framesize)
+	}
+
 	// Store args
 	for i, f := range we.Params {
 		p = appendp(p, AGet, regAddr(REG_SP))
@@ -1056,6 +1075,7 @@ var notUsePC_B = map[string]bool{
 	"runtime.gcWriteBarrier6": true,
 	"runtime.gcWriteBarrier7": true,
 	"runtime.gcWriteBarrier8": true,
+	"runtime.notInitialized":  true,
 	"runtime.wasmDiv":         true,
 	"runtime.wasmTruncS":      true,
 	"runtime.wasmTruncU":      true,
@@ -1121,7 +1141,8 @@ func assemble(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 		"runtime.gcWriteBarrier5",
 		"runtime.gcWriteBarrier6",
 		"runtime.gcWriteBarrier7",
-		"runtime.gcWriteBarrier8":
+		"runtime.gcWriteBarrier8",
+		"runtime.notInitialized":
 		// no locals
 		useAssemblyRegMap()
 	default:

src/cmd/link/internal/wasm/asm.go

@@ -87,6 +87,7 @@ var wasmFuncTypes = map[string]*wasmFuncType{
 	"runtime.gcWriteBarrier6": {Results: []byte{I64}},                                     // -> bufptr
 	"runtime.gcWriteBarrier7": {Results: []byte{I64}},                                     // -> bufptr
 	"runtime.gcWriteBarrier8": {Results: []byte{I64}},                                     // -> bufptr
+	"runtime.notInitialized":  {},                                                         //
 	"cmpbody":                 {Params: []byte{I64, I64, I64, I64}, Results: []byte{I64}}, // a, alen, b, blen -> -1/0/1
 	"memeqbody":               {Params: []byte{I64, I64, I64}, Results: []byte{I64}},      // a, b, len -> 0/1
 	"memcmp":                  {Params: []byte{I32, I32, I32}, Results: []byte{I32}},      // a, b, len -> <0/0/>0

src/runtime/asm_wasm.s

@@ -614,3 +614,13 @@ TEXT runtime·pause(SB), NOSPLIT, $0-8
 	I32Const $1
 	Set PAUSE
 	RETUNWIND
+
+// Called if a wasmexport function is called before runtime initialization
+TEXT runtime·notInitialized(SB), NOSPLIT, $0
+	MOVD $runtime·wasmStack+(m0Stack__size-16-8)(SB), SP
+	I32Const $0 // entry PC_B
+	Call runtime·notInitialized1(SB)
+	Drop
+	I32Const $0 // entry PC_B
+	Call runtime·abort(SB)
+	UNDEF

src/runtime/sys_wasm.go

@@ -34,3 +34,17 @@ func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
 	buf.pc = uintptr(fn)
 	buf.ctxt = ctxt
 }
+
+func notInitialized() // defined in assembly, call notInitialized1
+
+// Called if a wasmexport function is called before runtime initialization
+//
+//go:nosplit
+func notInitialized1() {
+	writeErrStr("runtime: wasmexport function called before runtime initialization\n")
+	if isarchive || islibrary {
+		writeErrStr("\tcall _initialize first\n")
+	} else {
+		writeErrStr("\tcall _start first\n")
+	}
+}