1 files changed, 48 insertions, 0 deletions
diff --git a/src/cmd/link/internal/ld/outbuf_darwin.go b/src/cmd/link/internal/ld/outbuf_darwin.go
new file mode 100644
index 0000000..17f7e2a
--- /dev/null
+++ b/src/cmd/link/internal/ld/outbuf_darwin.go
@@ -0,0 +1,48 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ld
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+// Implemented in the syscall package.
+//
+//go:linkname fcntl syscall.fcntl
+func fcntl(fd int, cmd int, arg int) (int, error)
+
+func (out *OutBuf) fallocate(size uint64) error {
+	stat, err := out.f.Stat()
+	if err != nil {
+		return err
+	}
+	// F_PEOFPOSMODE allocates from the end of the file, so we want the size difference.
+	// Apparently, it uses the end of the allocation, instead of the logical end of the
+	// file.
+	cursize := uint64(stat.Sys().(*syscall.Stat_t).Blocks * 512) // allocated size
+	if size <= cursize {
+		return nil
+	}
+
+	store := &syscall.Fstore_t{
+		Flags:   syscall.F_ALLOCATEALL,
+		Posmode: syscall.F_PEOFPOSMODE,
+		Offset:  0,
+		Length:  int64(size - cursize),
+	}
+
+	_, err = fcntl(int(out.f.Fd()), syscall.F_PREALLOCATE, int(uintptr(unsafe.Pointer(store))))
+	return err
+}
+
+func (out *OutBuf) purgeSignatureCache() {
+	// Apparently, the Darwin kernel may cache the code signature at mmap.
+	// When we mmap the output buffer, it doesn't have a code signature
+	// (as we haven't generated one). Invalidate the kernel cache now that
+	// we have generated the signature. See issue #42684.
+	msync(out.buf, syscall.MS_INVALIDATE)
+	// Best effort. Ignore error.
+}