unix: offs2lohi should shift by bits, not bytes
Fixes golang/go#57291
Change-Id: I212ab8a9f47563d9c124a0f20c17df35d7aa8e6d
Reviewed-on: https://go-review.googlesource.com/c/sys/+/457315
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
diff --git a/unix/syscall_linux.go b/unix/syscall_linux.go
index c5a9844..73b12b6 100644
--- a/unix/syscall_linux.go
+++ b/unix/syscall_linux.go
@@ -1986,12 +1986,10 @@
return iovecs
}
-// offs2lohi splits offs into its lower and upper unsigned long. On 64-bit
-// systems, hi will always be 0. On 32-bit systems, offs will be split in half.
-// preadv/pwritev chose this calling convention so they don't need to add a
-// padding-register for alignment on ARM.
+// offs2lohi splits offs into its low and high order bits.
func offs2lohi(offs int64) (lo, hi uintptr) {
- return uintptr(offs), uintptr(uint64(offs) >> SizeofLong)
+ const longBits = SizeofLong * 8
+ return uintptr(offs), uintptr(uint64(offs) >> longBits)
}
func Readv(fd int, iovs [][]byte) (n int, err error) {
diff --git a/unix/syscall_linux_test.go b/unix/syscall_linux_test.go
index 9fc641a..170e37e 100644
--- a/unix/syscall_linux_test.go
+++ b/unix/syscall_linux_test.go
@@ -1099,3 +1099,36 @@
dedupe.Info[1].Bytes_deduped, 0)
}
}
+
+// TestPwritevOffsets tests golang.org/issues/57291 where
+// offs2lohi was shifting by the size of long in bytes, not bits.
+func TestPwritevOffsets(t *testing.T) {
+ path := filepath.Join(t.TempDir(), "x.txt")
+
+ f, err := os.Create(path)
+ if err != nil {
+ t.Fatal(err)
+ }
+ t.Cleanup(func() { f.Close() })
+
+ const (
+ off = 20
+ )
+ b := [][]byte{{byte(0)}}
+ n, err := unix.Pwritev(int(f.Fd()), b, off)
+ if err != nil {
+ t.Fatal(err)
+ }
+ if n != len(b) {
+ t.Fatalf("expected to write %d, wrote %d", len(b), n)
+ }
+
+ info, err := f.Stat()
+ if err != nil {
+ t.Fatal(err)
+ }
+ want := off + int64(len(b))
+ if info.Size() != want {
+ t.Fatalf("expected size to be %d, got %d", want, info.Size())
+ }
+}
