outbuf_mmap.go

Documentation: cmd/link/internal/ld

     1  // Copyright 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build unix
     6  
     7  package ld
     8  
     9  import (
    10  	"syscall"
    11  )
    12  
    13  // Mmap maps the output file with the given size. It unmaps the old mapping
    14  // if it is already mapped. It also flushes any in-heap data to the new
    15  // mapping.
    16  func (out *OutBuf) Mmap(filesize uint64) (err error) {
    17  	oldlen := len(out.buf)
    18  	if oldlen != 0 {
    19  		out.munmap()
    20  	}
    21  
    22  	for {
    23  		if err = out.fallocate(filesize); err != syscall.EINTR {
    24  			break
    25  		}
    26  	}
    27  	if err != nil {
    28  		// Some file systems do not support fallocate. We ignore that error as linking
    29  		// can still take place, but you might SIGBUS when you write to the mmapped
    30  		// area.
    31  		if err != syscall.ENOTSUP && err != syscall.EPERM && err != errNoFallocate {
    32  			return err
    33  		}
    34  	}
    35  	err = out.f.Truncate(int64(filesize))
    36  	if err != nil {
    37  		Exitf("resize output file failed: %v", err)
    38  	}
    39  	out.buf, err = syscall.Mmap(int(out.f.Fd()), 0, int(filesize), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED|syscall.MAP_FILE)
    40  	if err != nil {
    41  		return err
    42  	}
    43  
    44  	// copy heap to new mapping
    45  	if uint64(oldlen+len(out.heap)) > filesize {
    46  		panic("mmap size too small")
    47  	}
    48  	copy(out.buf[oldlen:], out.heap)
    49  	out.heap = out.heap[:0]
    50  	return nil
    51  }
    52  
    53  func (out *OutBuf) munmap() {
    54  	if out.buf == nil {
    55  		return
    56  	}
    57  	syscall.Munmap(out.buf)
    58  	out.buf = nil
    59  }
    60
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