5 files changed, 24 insertions, 36 deletions
diff --git a/pkg/usermem/BUILD b/pkg/usermem/BUILD
index ff8b9e91a..6c9ada9c7 100644
--- a/pkg/usermem/BUILD
+++ b/pkg/usermem/BUILD
@@ -25,7 +25,6 @@ go_library(
         "bytes_io_unsafe.go",
         "usermem.go",
         "usermem_arm64.go",
-        "usermem_unsafe.go",
         "usermem_x86.go",
     ],
     visibility = ["//:sandbox"],
@@ -33,6 +32,7 @@ go_library(
         "//pkg/atomicbitops",
         "//pkg/binary",
         "//pkg/context",
+        "//pkg/gohacks",
         "//pkg/log",
         "//pkg/safemem",
         "//pkg/syserror",
diff --git a/pkg/usermem/addr.go b/pkg/usermem/addr.go
index e79210804..c4100481e 100644
--- a/pkg/usermem/addr.go
+++ b/pkg/usermem/addr.go
@@ -106,3 +106,20 @@ func (ar AddrRange) IsPageAligned() bool {
 func (ar AddrRange) String() string {
 	return fmt.Sprintf("[%#x, %#x)", ar.Start, ar.End)
 }
+
+// PageRoundDown/Up are equivalent to Addr.RoundDown/Up, but without the
+// potentially truncating conversion from uint64 to Addr. This is necessary
+// because there is no way to define generic "PageRoundDown/Up" functions in Go.
+
+// PageRoundDown returns x rounded down to the nearest page boundary.
+func PageRoundDown(x uint64) uint64 {
+	return x &^ (PageSize - 1)
+}
+
+// PageRoundUp returns x rounded up to the nearest page boundary.
+// ok is true iff rounding up did not wrap around.
+func PageRoundUp(x uint64) (addr uint64, ok bool) {
+	addr = PageRoundDown(x + PageSize - 1)
+	ok = addr >= x
+	return
+}
diff --git a/pkg/usermem/usermem.go b/pkg/usermem/usermem.go
index 71fd4e155..cd6a0ea6b 100644
--- a/pkg/usermem/usermem.go
+++ b/pkg/usermem/usermem.go
@@ -23,14 +23,12 @@ import (
 
 	"gvisor.dev/gvisor/pkg/binary"
 	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/gohacks"
 	"gvisor.dev/gvisor/pkg/safemem"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
 // IO provides access to the contents of a virtual memory space.
-//
-// FIXME(b/38173783): Implementations of IO cannot expect ctx to contain any
-// meaningful data.
 type IO interface {
 	// CopyOut copies len(src) bytes from src to the memory mapped at addr. It
 	// returns the number of bytes copied. If the number of bytes copied is <
@@ -251,7 +249,7 @@ func CopyStringIn(ctx context.Context, uio IO, addr Addr, maxlen int, opts IOOpt
 		}
 		end, ok := addr.AddLength(uint64(readlen))
 		if !ok {
-			return stringFromImmutableBytes(buf[:done]), syserror.EFAULT
+			return gohacks.StringFromImmutableBytes(buf[:done]), syserror.EFAULT
 		}
 		// Shorten the read to avoid crossing page boundaries, since faulting
 		// in a page unnecessarily is expensive. This also ensures that partial
@@ -272,16 +270,16 @@ func CopyStringIn(ctx context.Context, uio IO, addr Addr, maxlen int, opts IOOpt
 		// Look for the terminating zero byte, which may have occurred before
 		// hitting err.
 		if i := bytes.IndexByte(buf[done:done+n], byte(0)); i >= 0 {
-			return stringFromImmutableBytes(buf[:done+i]), nil
+			return gohacks.StringFromImmutableBytes(buf[:done+i]), nil
 		}
 
 		done += n
 		if err != nil {
-			return stringFromImmutableBytes(buf[:done]), err
+			return gohacks.StringFromImmutableBytes(buf[:done]), err
 		}
 		addr = end
 	}
-	return stringFromImmutableBytes(buf), syserror.ENAMETOOLONG
+	return gohacks.StringFromImmutableBytes(buf), syserror.ENAMETOOLONG
 }
 
 // CopyOutVec copies bytes from src to the memory mapped at ars in uio. The
diff --git a/pkg/usermem/usermem_unsafe.go b/pkg/usermem/usermem_unsafe.go
deleted file mode 100644
index 876783e78..000000000
--- a/pkg/usermem/usermem_unsafe.go
+++ /dev/null
@@ -1,27 +0,0 @@
-// Copyright 2019 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 usermem
-
-import (
-	"unsafe"
-)
-
-// stringFromImmutableBytes is equivalent to string(bs), except that it never
-// copies even if escape analysis can't prove that bs does not escape. This is
-// only valid if bs is never mutated after stringFromImmutableBytes returns.
-func stringFromImmutableBytes(bs []byte) string {
-	// Compare strings.Builder.String().
-	return *(*string)(unsafe.Pointer(&bs))
-}
diff --git a/pkg/usermem/usermem_x86.go b/pkg/usermem/usermem_x86.go
index 8059b72d2..d96f829fb 100644
--- a/pkg/usermem/usermem_x86.go
+++ b/pkg/usermem/usermem_x86.go
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// +build amd64 i386
+// +build amd64 386
 
 package usermem