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authorJamie Liu <jamieliu@google.com>2021-09-01 14:04:50 -0700
committergVisor bot <gvisor-bot@google.com>2021-09-01 14:07:57 -0700
commitb4de26d6b1bbb0e75187690da6d3fe120f53656b (patch)
treef34266f08c7ea44369231969b48aacc733910399
parent702fe7d60da4d38344f00200187fe1f0766bef8d (diff)
Don't use reflection in fpu.alignedBytes.
reflect.ValueOf takes an interface{}, so when passed a slice the compiler emits a call to runtime.convTslice to heap-allocate a copy of the slice header. PiperOrigin-RevId: 394310052
-rw-r--r--pkg/sentry/arch/fpu/BUILD1
-rw-r--r--pkg/sentry/arch/fpu/fpu.go13
-rw-r--r--pkg/sentry/arch/fpu/fpu_unsafe.go31
3 files changed, 32 insertions, 13 deletions
diff --git a/pkg/sentry/arch/fpu/BUILD b/pkg/sentry/arch/fpu/BUILD
index 6cdd21b1b..1f371e513 100644
--- a/pkg/sentry/arch/fpu/BUILD
+++ b/pkg/sentry/arch/fpu/BUILD
@@ -9,6 +9,7 @@ go_library(
"fpu_amd64.go",
"fpu_amd64.s",
"fpu_arm64.go",
+ "fpu_unsafe.go",
],
visibility = ["//:sandbox"],
deps = [
diff --git a/pkg/sentry/arch/fpu/fpu.go b/pkg/sentry/arch/fpu/fpu.go
index 867d309a3..62bde19d3 100644
--- a/pkg/sentry/arch/fpu/fpu.go
+++ b/pkg/sentry/arch/fpu/fpu.go
@@ -17,7 +17,6 @@ package fpu
import (
"fmt"
- "reflect"
)
// State represents floating point state.
@@ -40,15 +39,3 @@ type ErrLoadingState struct {
func (e ErrLoadingState) Error() string {
return fmt.Sprintf("floating point state contains unsupported features; supported: %#x saved: %#x", e.supportedFeatures, e.savedFeatures)
}
-
-// alignedBytes returns a slice of size bytes, aligned in memory to the given
-// alignment. This is used because we require certain structures to be aligned
-// in a specific way (for example, the X86 floating point data).
-func alignedBytes(size, alignment uint) []byte {
- data := make([]byte, size+alignment-1)
- offset := uint(reflect.ValueOf(data).Index(0).Addr().Pointer() % uintptr(alignment))
- if offset == 0 {
- return data[:size:size]
- }
- return data[alignment-offset:][:size:size]
-}
diff --git a/pkg/sentry/arch/fpu/fpu_unsafe.go b/pkg/sentry/arch/fpu/fpu_unsafe.go
new file mode 100644
index 000000000..c91dc99be
--- /dev/null
+++ b/pkg/sentry/arch/fpu/fpu_unsafe.go
@@ -0,0 +1,31 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fpu
+
+import (
+ "unsafe"
+)
+
+// alignedBytes returns a slice of size bytes, aligned in memory to the given
+// alignment. This is used because we require certain structures to be aligned
+// in a specific way (for example, the X86 floating point data).
+func alignedBytes(size, alignment uint) []byte {
+ data := make([]byte, size+alignment-1)
+ offset := uint(uintptr(unsafe.Pointer(&data[0])) % uintptr(alignment))
+ if offset == 0 {
+ return data[:size:size]
+ }
+ return data[alignment-offset:][:size:size]
+}