runtime: fix off-by-one error finding module for PC

Also fix compiler-invoked panics to avoid a confusing "malloc deadlock"
crash if they are invoked while executing the runtime.

Fixes #14599.

Change-Id: I89436abcbf3587901909abbdca1973301654a76e
Reviewed-on: https://go-review.googlesource.com/20219
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-on: https://go-review.googlesource.com/22042Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/crash_cgo_test.go

@@ -178,3 +178,11 @@ func TestCgoCheckBytes(t *testing.T) {
 		t.Errorf("cgo check too slow: got %v, expected at most %v", d1, d2*10)
 	}
 }
+
+func TestCgoCCodeSIGPROF(t *testing.T) {
+	got := runTestProg(t, "testprogcgo", "CgoCCodeSIGPROF")
+	want := "OK\n"
+	if got != want {
+		t.Errorf("expected %q got %v", want, got)
+	}
+}

src/runtime/panic.go

@@ -9,39 +9,56 @@ import (
 	"unsafe"
 )
 
+// Calling panic with one of the errors below will call errorString.Error
+// which will call mallocgc to concatenate strings. That will fail if
+// malloc is locked, causing a confusing error message. Throw a better
+// error message instead.
+func panicCheckMalloc(err error) {
+	gp := getg()
+	if gp != nil && gp.m != nil && gp.m.mallocing != 0 {
+		throw(string(err.(errorString)))
+	}
+}
+
 var indexError = error(errorString("index out of range"))
 
 func panicindex() {
+	panicCheckMalloc(indexError)
 	panic(indexError)
 }
 
 var sliceError = error(errorString("slice bounds out of range"))
 
 func panicslice() {
+	panicCheckMalloc(sliceError)
 	panic(sliceError)
 }
 
 var divideError = error(errorString("integer divide by zero"))
 
 func panicdivide() {
+	panicCheckMalloc(divideError)
 	panic(divideError)
 }
 
 var overflowError = error(errorString("integer overflow"))
 
 func panicoverflow() {
+	panicCheckMalloc(overflowError)
 	panic(overflowError)
 }
 
 var floatError = error(errorString("floating point error"))
 
 func panicfloat() {
+	panicCheckMalloc(floatError)
 	panic(floatError)
 }
 
 var memoryError = error(errorString("invalid memory address or nil pointer dereference"))
 
 func panicmem() {
+	panicCheckMalloc(memoryError)
 	panic(memoryError)
 }
 

src/runtime/symtab.go

@@ -199,7 +199,7 @@ func (f *Func) FileLine(pc uintptr) (file string, line int) {
 
 func findmoduledatap(pc uintptr) *moduledata {
 	for datap := &firstmoduledata; datap != nil; datap = datap.next {
-		if datap.minpc <= pc && pc <= datap.maxpc {
+		if datap.minpc <= pc && pc < datap.maxpc {
 			return datap
 		}
 	}

src/runtime/testdata/testprogcgo/aprof.go

+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+// Test that SIGPROF received in C code does not crash the process
+// looking for the C code's func pointer.
+
+// The test fails when the function is the first C function.
+// The exported functions are the first C functions, so we use that.
+
+// extern void GoNop();
+import "C"
+
+import (
+	"bytes"
+	"fmt"
+	"runtime/pprof"
+)
+
+func init() {
+	register("CgoCCodeSIGPROF", CgoCCodeSIGPROF)
+}
+
+//export GoNop
+func GoNop() {}
+
+func CgoCCodeSIGPROF() {
+	c := make(chan bool)
+	go func() {
+		for {
+			<-c
+			for i := 0; i < 1e7; i++ {
+				C.GoNop()
+			}
+			c <- true
+		}
+	}()
+
+	var buf bytes.Buffer
+	pprof.StartCPUProfile(&buf)
+	c <- true
+	<-c
+	pprof.StopCPUProfile()
+
+	fmt.Println("OK")
+}