misc/cgo/errors: fix malloc test for dragonfly

The Dragonfly libc returns a non-zero value for malloc(-1).

Fixes #17585.

Change-Id: Icfe68011ccbc75c676273ee3c3efdf24a520a004
Reviewed-on: https://go-review.googlesource.com/32050
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

misc/cgo/errors/malloc.go

@@ -11,10 +11,21 @@ import "C"
 
 import (
 	"fmt"
+	"runtime"
 )
 
 func main() {
-	p := C.malloc(C.size_t(^uintptr(0)))
+	var size C.size_t
+	size--
+
+	// The Dragonfly libc succeeds when asked to allocate
+	// 0xffffffffffffffff bytes, so pass a different value that
+	// causes it to fail.
+	if runtime.GOOS == "dragonfly" {
+		size = C.size_t(0x7fffffff << (32 * (^uintptr(0) >> 63)))
+	}
+
+	p := C.malloc(size)
 	if p == nil {
 		fmt.Println("malloc: C.malloc returned nil")
 		// Just exit normally--the test script expects this

misc/cgo/errors/test.bash

@@ -62,7 +62,7 @@ fi
 # The malloc.go test should crash.
 rm -f malloc.out
 if go run malloc.go >malloc.out 2>&1; then
-	echo "`go run malloc.go` succeeded unexpectedly"
+	echo '`go run malloc.go` succeeded unexpectedly'
 	cat malloc.out
 	rm -f malloc.out
 	exit 1