runtime: don't panic for bad size hint in hashmap

Because the hint parameter is supposed to be treated
purely as a hint, if it doesn't meet the requirements
we disregard it and continue as if there was no hint
at all.

Fixes #19926

Change-Id: I86e7f99472fad6b99ba4e2fd33e4a9e55d55115e
Reviewed-on: https://go-review.googlesource.com/40854
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

3 files changed, 10 insertions, 14 deletions

diff --git a/src/runtime/hashmap.go b/src/runtime/hashmap.go
index c6c2fa5fdf..11ce0cbc4b 100644
--- a/src/runtime/hashmap.go
+++ b/src/runtime/hashmap.go
@@ -255,9 +255,8 @@ func makemap(t *maptype, hint int64, h *hmap, bucket unsafe.Pointer) *hmap {
 		throw("bad hmap size")
 	}
 
-	if hint < 0 || int64(int32(hint)) != hint {
-		panic(plainError("makemap: size out of range"))
-		// TODO: make hint an int, then none of this nonsense
+	if hint < 0 || hint > int64(maxSliceCap(t.bucket.size)) {
+		hint = 0
 	}
 
 	if !ismapkey(t.key) {
diff --git a/src/runtime/map_test.go b/src/runtime/map_test.go
index 45d14126c2..81f05a0613 100644
--- a/src/runtime/map_test.go
+++ b/src/runtime/map_test.go
@@ -588,6 +588,14 @@ func TestMapLargeValNoPointer(t *testing.T) {
 	}
 }
 
+// Test that making a map with a large or invalid hint
+// doesn't panic. (Issue 19926).
+func TestIgnoreBogusMapHint(t *testing.T) {
+	for _, hint := range []int64{-1, 1 << 62} {
+		_ = make(map[int]int, hint)
+	}
+}
+
 func benchmarkMapPop(b *testing.B, n int) {
 	m := map[int]int{}
 	for i := 0; i < b.N; i++ {
diff --git a/test/fixedbugs/bug273.go b/test/fixedbugs/bug273.go
index b6258d54fc..c04f2116c5 100644
--- a/test/fixedbugs/bug273.go
+++ b/test/fixedbugs/bug273.go
@@ -48,15 +48,6 @@ func bigcap() {
 	g1 = make([]block, 10, big)
 }
 
-var g3 map[block]block
-func badmapcap() {
-	g3 = make(map[block]block, minus1)
-}
-
-func bigmapcap() {
-	g3 = make(map[block]block, big)
-}
-
 type cblock [1<<16-1]byte
 
 var g4 chan cblock
@@ -78,8 +69,6 @@ func main() {
 	shouldfail(badcap, "badcap")
 	shouldfail(badcap1, "badcap1")
 	shouldfail(bigcap, "bigcap")
-	shouldfail(badmapcap, "badmapcap")
-	shouldfail(bigmapcap, "bigmapcap")
 	shouldfail(badchancap, "badchancap")
 	shouldfail(bigchancap, "bigchancap")
 	shouldfail(overflowchan, "overflowchan")