Merge lp:~mwhudson/mgo/evaluation-order into lp:mgo/v2

[Michael Hudson-Doyle]

bson: don't trust expression evaluation order

The evaluation order of

  end := d.i - 4 + int(d.readInt32())

differs when compiled with gccgo vs the gc toolchain, and is
apparently unspecified according to the spec.

[Dave Cheney (dave-cheney)]

I've raised the question on the gccgo mailing list.

https://groups.google.com/d/msg/gofrontend-dev/y5g92hnEGfg/6tYHbfw-YtcJ

[Gustavo Niemeyer (niemeyer)]

*** Submitted:

bson: don't trust expression evaluation order

The evaluation order of

  end := d.i - 4 + int(d.readInt32())

differs when compiled with gccgo vs the gc toolchain, and is
apparently unspecified according to the spec.

[Gustavo Niemeyer (niemeyer)]

Thanks!

=== modified file 'bson/decode.go'
--- bson/decode.go	2013-08-04 23:00:08 +0000
+++ bson/decode.go	2013-11-13 01:35:47 +0000
@@ -214,7 +214,8 @@
 		panic("Unsupported document type for unmarshalling: " + out.Type().String())
 	}
 
-	end := d.i - 4 + int(d.readInt32())
+	end := int(d.readInt32())
+	end += d.i - 4
 	if end <= d.i || end > len(d.in) || d.in[end-1] != '\x00' {
 		corrupted()
 	}
@@ -272,7 +273,8 @@
 }
 
 func (d *decoder) readArrayDocTo(out reflect.Value) {
-	end := d.i - 4 + int(d.readInt32())
+	end := int(d.readInt32())
+	end += d.i - 4
 	if end <= d.i || end > len(d.in) || d.in[end-1] != '\x00' {
 		corrupted()
 	}
@@ -309,7 +311,8 @@
 	tmp := make([]reflect.Value, 0, 8)
 	elemType := t.Elem()
 
-	end := d.i - 4 + int(d.readInt32())
+	end := int(d.readInt32())
+	end += d.i - 4
 	if end <= d.i || end > len(d.in) || d.in[end-1] != '\x00' {
 		corrupted()
 	}
@@ -381,7 +384,8 @@
 }
 
 func (d *decoder) readDocWith(f func(kind byte, name string)) {
-	end := d.i - 4 + int(d.readInt32())
+	end := int(d.readInt32())
+	end += d.i - 4
 	if end <= d.i || end > len(d.in) || d.in[end-1] != '\x00' {
 		corrupted()
 	}