runtime: fetch physical page size from the OS

Currently the physical page size assumed by the runtime is hard-coded.
On Linux the runtime at least fetches the OS page size during init and
sanity checks against the hard-coded value, but they may still differ.
On other OSes we wouldn't even notice.

Add support on all OSes to fetch the actual OS physical page size
during runtime init and lift the sanity check of PhysPageSize from the
Linux init code to general malloc init. Currently this is the only use
of the retrieved page size, but we'll add more shortly.

Updates #12480 and #10180.

Change-Id: I065f2834bc97c71d3208edc17fd990ec9058b6da
Reviewed-on: https://go-review.googlesource.com/25050
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

1 files changed, 26 insertions, 2 deletions

diff --git a/src/runtime/runtime_mmap_test.go b/src/runtime/runtime_mmap_test.go
index cf240c1350..2eca6b9e88 100644
--- a/src/runtime/runtime_mmap_test.go
+++ b/src/runtime/runtime_mmap_test.go
@@ -8,15 +8,15 @@ package runtime_test
 
 import (
 	"runtime"
-	"runtime/internal/sys"
 	"testing"
+	"unsafe"
 )
 
 // Test that the error value returned by mmap is positive, as that is
 // what the code in mem_bsd.go, mem_darwin.go, and mem_linux.go expects.
 // See the uses of ENOMEM in sysMap in those files.
 func TestMmapErrorSign(t *testing.T) {
-	p := runtime.Mmap(nil, ^uintptr(0)&^(sys.PhysPageSize-1), 0, runtime.MAP_ANON|runtime.MAP_PRIVATE, -1, 0)
+	p := runtime.Mmap(nil, ^uintptr(0)&^(runtime.GetPhysPageSize()-1), 0, runtime.MAP_ANON|runtime.MAP_PRIVATE, -1, 0)
 
 	// The runtime.mmap function is nosplit, but t.Errorf is not.
 	// Reset the pointer so that we don't get an "invalid stack
@@ -28,3 +28,27 @@ func TestMmapErrorSign(t *testing.T) {
 		t.Errorf("mmap = %v, want %v", v, runtime.ENOMEM)
 	}
 }
+
+func TestPhysPageSize(t *testing.T) {
+	// Mmap fails if the address is not page aligned, so we can
+	// use this to test if the page size is the true page size.
+	ps := runtime.GetPhysPageSize()
+
+	// Get a region of memory to play with. This should be page-aligned.
+	b := uintptr(runtime.Mmap(nil, 2*ps, 0, runtime.MAP_ANON|runtime.MAP_PRIVATE, -1, 0))
+	if b < 4096 {
+		t.Fatalf("Mmap: %v", b)
+	}
+
+	// Mmap should fail at a half page into the buffer.
+	err := uintptr(runtime.Mmap(unsafe.Pointer(uintptr(b)+ps/2), ps, 0, runtime.MAP_ANON|runtime.MAP_PRIVATE|runtime.MAP_FIXED, -1, 0))
+	if err >= 4096 {
+		t.Errorf("Mmap should have failed with half-page alignment %d, but succeeded: %v", ps/2, err)
+	}
+
+	// Mmap should succeed at a full page into the buffer.
+	err = uintptr(runtime.Mmap(unsafe.Pointer(uintptr(b)+ps), ps, 0, runtime.MAP_ANON|runtime.MAP_PRIVATE|runtime.MAP_FIXED, -1, 0))
+	if err < 4096 {
+		t.Errorf("Mmap at full-page alignment %d failed: %v", ps, err)
+	}
+}