1 files changed, 59 insertions, 0 deletions
diff --git a/src/cmd/link/internal/ld/outbuf_mmap.go b/src/cmd/link/internal/ld/outbuf_mmap.go
new file mode 100644
index 0000000..7bb728a
--- /dev/null
+++ b/src/cmd/link/internal/ld/outbuf_mmap.go
@@ -0,0 +1,59 @@
+// Copyright 2019 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.
+
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || (solaris && go1.20)
+
+package ld
+
+import (
+	"syscall"
+)
+
+// Mmap maps the output file with the given size. It unmaps the old mapping
+// if it is already mapped. It also flushes any in-heap data to the new
+// mapping.
+func (out *OutBuf) Mmap(filesize uint64) (err error) {
+	oldlen := len(out.buf)
+	if oldlen != 0 {
+		out.munmap()
+	}
+
+	for {
+		if err = out.fallocate(filesize); err != syscall.EINTR {
+			break
+		}
+	}
+	if err != nil {
+		// Some file systems do not support fallocate. We ignore that error as linking
+		// can still take place, but you might SIGBUS when you write to the mmapped
+		// area.
+		if err != syscall.ENOTSUP && err != syscall.EPERM && err != errNoFallocate {
+			return err
+		}
+	}
+	err = out.f.Truncate(int64(filesize))
+	if err != nil {
+		Exitf("resize output file failed: %v", err)
+	}
+	out.buf, err = syscall.Mmap(int(out.f.Fd()), 0, int(filesize), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED|syscall.MAP_FILE)
+	if err != nil {
+		return err
+	}
+
+	// copy heap to new mapping
+	if uint64(oldlen+len(out.heap)) > filesize {
+		panic("mmap size too small")
+	}
+	copy(out.buf[oldlen:], out.heap)
+	out.heap = out.heap[:0]
+	return nil
+}
+
+func (out *OutBuf) munmap() {
+	if out.buf == nil {
+		return
+	}
+	syscall.Munmap(out.buf)
+	out.buf = nil
+}