mremap_size.go raw

   1  //go:build linux && !arm64 && !arm && !js
   2  // +build linux,!arm64,!arm,!js
   3  
   4  /*
   5   * SPDX-FileCopyrightText: © Hypermode Inc. <hello@hypermode.com>
   6   * SPDX-License-Identifier: Apache-2.0
   7   */
   8  
   9  package z
  10  
  11  import (
  12  	"fmt"
  13  	"reflect"
  14  	"unsafe"
  15  
  16  	"golang.org/x/sys/unix"
  17  )
  18  
  19  // mremap is a Linux-specific system call to remap pages in memory. This can be used in place of munmap + mmap.
  20  func mremap(data []byte, size int) ([]byte, error) {
  21  	//nolint:lll
  22  	// taken from <https://github.com/torvalds/linux/blob/f8394f232b1eab649ce2df5c5f15b0e528c92091/include/uapi/linux/mman.h#L8>
  23  	const MREMAP_MAYMOVE = 0x1
  24  
  25  	header := (*reflect.SliceHeader)(unsafe.Pointer(&data))
  26  	mmapAddr, mmapSize, errno := unix.Syscall6(
  27  		unix.SYS_MREMAP,
  28  		header.Data,
  29  		uintptr(header.Len),
  30  		uintptr(size),
  31  		uintptr(MREMAP_MAYMOVE),
  32  		0,
  33  		0,
  34  	)
  35  	if errno != 0 {
  36  		return nil, errno
  37  	}
  38  	if mmapSize != uintptr(size) {
  39  		return nil, fmt.Errorf("mremap size mismatch: requested: %d got: %d", size, mmapSize)
  40  	}
  41  
  42  	header.Data = mmapAddr
  43  	header.Cap = size
  44  	header.Len = size
  45  	return data, nil
  46  }
  47