runtime: improve atoi implementation

- Adds overflow checks
- Adds parsing of negative integers
- Adds boolean return value to signal parsing errors
- Adds atoi32 for parsing of integers that fit in an int32
- Adds tests

Handling of errors to provide error messages
at the call sites is left to future CLs.

Updates #17718

Change-Id: I3cacd0ab1230b9efc5404c68edae7304d39bcbc0
Reviewed-on: https://go-review.googlesource.com/32390
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

6 files changed, 174 insertions, 20 deletions

diff --git a/src/runtime/export_test.go b/src/runtime/export_test.go
index d83b3b0a49..f4a65fec18 100644
--- a/src/runtime/export_test.go
+++ b/src/runtime/export_test.go
@@ -32,6 +32,9 @@ var FuncPC = funcPC
 
 var Fastlog2 = fastlog2
 
+var Atoi = atoi
+var Atoi32 = atoi32
+
 type LFNode struct {
 	Next    uint64
 	Pushcnt uintptr
diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index 64af0a90ee..c625b75ea9 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -196,13 +196,13 @@ func gcinit() {
 
 func readgogc() int32 {
 	p := gogetenv("GOGC")
-	if p == "" {
-		return 100
-	}
 	if p == "off" {
 		return -1
 	}
-	return int32(atoi(p))
+	if n, ok := atoi32(p); ok {
+		return n
+	}
+	return 100
 }
 
 // gcenable is called after the bulk of the runtime initialization,
diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 6fb85c832d..c83644e810 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -477,17 +477,14 @@ func schedinit() {
 	gcinit()
 
 	sched.lastpoll = uint64(nanotime())
-	procs := int(ncpu)
+	procs := ncpu
+	if n, ok := atoi32(gogetenv("GOMAXPROCS")); ok && n > 0 {
+		procs = n
+	}
 	if procs > _MaxGomaxprocs {
 		procs = _MaxGomaxprocs
 	}
-	if n := atoi(gogetenv("GOMAXPROCS")); n > 0 {
-		if n > _MaxGomaxprocs {
-			n = _MaxGomaxprocs
-		}
-		procs = n
-	}
-	if procresize(int32(procs)) != nil {
+	if procresize(procs) != nil {
 		throw("unknown runnable goroutine during bootstrap")
 	}
 
diff --git a/src/runtime/runtime1.go b/src/runtime/runtime1.go
index 0acb37212e..780e1d907a 100644
--- a/src/runtime/runtime1.go
+++ b/src/runtime/runtime1.go
@@ -375,11 +375,15 @@ func parsedebugvars() {
 		// is int, not int32, and should only be updated
 		// if specified in GODEBUG.
 		if key == "memprofilerate" {
-			MemProfileRate = atoi(value)
+			if n, ok := atoi(value); ok {
+				MemProfileRate = n
+			}
 		} else {
 			for _, v := range dbgvars {
 				if v.name == key {
-					*v.value = int32(atoi(value))
+					if n, ok := atoi32(value); ok {
+						*v.value = n
+					}
 				}
 			}
 		}
@@ -422,7 +426,10 @@ func setTraceback(level string) {
 	case "crash":
 		t = 2<<tracebackShift | tracebackAll | tracebackCrash
 	default:
-		t = uint32(atoi(level))<<tracebackShift | tracebackAll
+		t = tracebackAll
+		if n, ok := atoi(level); ok && n == int(uint32(n)) {
+			t |= uint32(n) << tracebackShift
+		}
 	}
 	// when C owns the process, simply exit'ing the process on fatal errors
 	// and panics is surprising. Be louder and abort instead.
diff --git a/src/runtime/string.go b/src/runtime/string.go
index 07528236ee..822adaacf1 100644
--- a/src/runtime/string.go
+++ b/src/runtime/string.go
@@ -320,13 +320,66 @@ func hasprefix(s, t string) bool {
 	return len(s) >= len(t) && s[:len(t)] == t
 }
 
-func atoi(s string) int {
-	n := 0
-	for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
-		n = n*10 + int(s[0]) - '0'
+const (
+	maxUint = ^uint(0)
+	maxInt  = int(maxUint >> 1)
+)
+
+// atoi parses an int from a string s.
+// The bool result reports whether s is a number
+// representable by a value of type int.
+func atoi(s string) (int, bool) {
+	if s == "" {
+		return 0, false
+	}
+
+	neg := false
+	if s[0] == '-' {
+		neg = true
 		s = s[1:]
 	}
-	return n
+
+	un := uint(0)
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		if c < '0' || c > '9' {
+			return 0, false
+		}
+		if un > maxUint/10 {
+			// overflow
+			return 0, false
+		}
+		un *= 10
+		un1 := un + uint(c) - '0'
+		if un1 < un {
+			// overflow
+			return 0, false
+		}
+		un = un1
+	}
+
+	if !neg && un > uint(maxInt) {
+		return 0, false
+	}
+	if neg && un > uint(maxInt)+1 {
+		return 0, false
+	}
+
+	n := int(un)
+	if neg {
+		n = -n
+	}
+
+	return n, true
+}
+
+// atoi32 is like atoi but for integers
+// that fit into an int32.
+func atoi32(s string) (int32, bool) {
+	if n, ok := atoi(s); n == int(int32(n)) {
+		return int32(n), ok
+	}
+	return 0, false
 }
 
 //go:nosplit
diff --git a/src/runtime/string_test.go b/src/runtime/string_test.go
index ef0b01c237..fcfc52291f 100644
--- a/src/runtime/string_test.go
+++ b/src/runtime/string_test.go
@@ -279,3 +279,97 @@ func TestString2Slice(t *testing.T) {
 		t.Errorf("extra runes not zeroed")
 	}
 }
+
+const intSize = 32 << (^uint(0) >> 63)
+
+type atoi64Test struct {
+	in  string
+	out int64
+	ok  bool
+}
+
+var atoi64tests = []atoi64Test{
+	{"", 0, false},
+	{"0", 0, true},
+	{"-0", 0, true},
+	{"1", 1, true},
+	{"-1", -1, true},
+	{"12345", 12345, true},
+	{"-12345", -12345, true},
+	{"012345", 12345, true},
+	{"-012345", -12345, true},
+	{"12345x", 0, false},
+	{"-12345x", 0, false},
+	{"98765432100", 98765432100, true},
+	{"-98765432100", -98765432100, true},
+	{"20496382327982653440", 0, false},
+	{"-20496382327982653440", 0, false},
+	{"9223372036854775807", 1<<63 - 1, true},
+	{"-9223372036854775807", -(1<<63 - 1), true},
+	{"9223372036854775808", 0, false},
+	{"-9223372036854775808", -1 << 63, true},
+	{"9223372036854775809", 0, false},
+	{"-9223372036854775809", 0, false},
+}
+
+func TestAtoi(t *testing.T) {
+	switch intSize {
+	case 32:
+		for i := range atoi32tests {
+			test := &atoi32tests[i]
+			out, ok := runtime.Atoi(test.in)
+			if test.out != int32(out) || test.ok != ok {
+				t.Errorf("atoi(%q) = (%v, %v) want (%v, %v)",
+					test.in, out, ok, test.out, test.ok)
+			}
+		}
+	case 64:
+		for i := range atoi64tests {
+			test := &atoi64tests[i]
+			out, ok := runtime.Atoi(test.in)
+			if test.out != int64(out) || test.ok != ok {
+				t.Errorf("atoi(%q) = (%v, %v) want (%v, %v)",
+					test.in, out, ok, test.out, test.ok)
+			}
+		}
+	}
+}
+
+type atoi32Test struct {
+	in  string
+	out int32
+	ok  bool
+}
+
+var atoi32tests = []atoi32Test{
+	{"", 0, false},
+	{"0", 0, true},
+	{"-0", 0, true},
+	{"1", 1, true},
+	{"-1", -1, true},
+	{"12345", 12345, true},
+	{"-12345", -12345, true},
+	{"012345", 12345, true},
+	{"-012345", -12345, true},
+	{"12345x", 0, false},
+	{"-12345x", 0, false},
+	{"987654321", 987654321, true},
+	{"-987654321", -987654321, true},
+	{"2147483647", 1<<31 - 1, true},
+	{"-2147483647", -(1<<31 - 1), true},
+	{"2147483648", 0, false},
+	{"-2147483648", -1 << 31, true},
+	{"2147483649", 0, false},
+	{"-2147483649", 0, false},
+}
+
+func TestAtoi32(t *testing.T) {
+	for i := range atoi32tests {
+		test := &atoi32tests[i]
+		out, ok := runtime.Atoi32(test.in)
+		if test.out != out || test.ok != ok {
+			t.Errorf("atoi32(%q) = (%v, %v) want (%v, %v)",
+				test.in, out, ok, test.out, test.ok)
+		}
+	}
+}