[dev.garbage] runtime: document sysAlloc

In particular, it always returns an aligned pointer.

Change-Id: I763789a539a4bfd8b0efb36a39a80be1a479d3e2
Reviewed-on: https://go-review.googlesource.com/22558
Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index ec4939f1dd4e10e0bb950434185fa0e66c315f15..2d8905b88ddf2825810bf6c3e2eb85bd6d042032 100644 (file)
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -387,6 +387,10 @@ func sysReserveHigh(n uintptr, reserved *bool) unsafe.Pointer {
        return sysReserve(nil, n, reserved)
 }
 
+// sysAlloc allocates the next n bytes from the heap arena. The
+// returned pointer is always _PageSize aligned and between
+// h.arena_start and h.arena_end. sysAlloc returns nil on failure.
+// There is no corresponding free function.
 func (h *mheap) sysAlloc(n uintptr) unsafe.Pointer {
        if n > h.arena_end-h.arena_used {
                // We are in 32-bit mode, maybe we didn't use all possible address space yet.