LXR linux/tools/testing/selftests/x86/thunks.S

   1/* SPDX-License-Identifier: GPL-2.0-only */
   2/*
   3 * thunks.S - assembly helpers for mixed-bitness code
   4 * Copyright (c) 2015 Andrew Lutomirski
   5 *
   6 * These are little helpers that make it easier to switch bitness on
   7 * the fly.
   8 */
   9
  10        .text
  11
  12        .global call32_from_64
  13        .type call32_from_64, @function
  14call32_from_64:
  15        // rdi: stack to use
  16        // esi: function to call
  17
  18        // Save registers
  19        pushq %rbx
  20        pushq %rbp
  21        pushq %r12
  22        pushq %r13
  23        pushq %r14
  24        pushq %r15
  25        pushfq
  26
  27        // Switch stacks
  28        mov %rsp,(%rdi)
  29        mov %rdi,%rsp
  30
  31        // Switch to compatibility mode
  32        pushq $0x23  /* USER32_CS */
  33        pushq $1f
  34        lretq
  35
  361:
  37        .code32
  38        // Call the function
  39        call *%esi
  40        // Switch back to long mode
  41        jmp $0x33,$1f
  42        .code64
  43
  441:
  45        // Restore the stack
  46        mov (%rsp),%rsp
  47
  48        // Restore registers
  49        popfq
  50        popq %r15
  51        popq %r14
  52        popq %r13
  53        popq %r12
  54        popq %rbp
  55        popq %rbx
  56
  57        ret
  58
  59.size call32_from_64, .-call32_from_64
  60
  61.section .note.GNU-stack,"",%progbits
  62