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/*
* thunks.S - assembly helpers for mixed-bitness code
* Copyright (c) 2015 Andrew Lutomirski
*
* This program is free software; you can redistribute it and/or modify
* it under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* These are little helpers that make it easier to switch bitness on
* the fly.
*/
.text
.global call32_from_64
.type call32_from_64, @function
call32_from_64:
// rdi: stack to use
// esi: function to call
// Save registers
pushq %rbx
pushq %rbp
pushq %r12
pushq %r13
pushq %r14
pushq %r15
pushfq
// Switch stacks
mov %rsp,(%rdi)
mov %rdi,%rsp
// Switch to compatibility mode
pushq $0x23 /* USER32_CS */
pushq $1f
lretq
1:
.code32
// Call the function
call *%esi
// Switch back to long mode
jmp $0x33,$1f
.code64
1:
// Restore the stack
mov (%rsp),%rsp
// Restore registers
popfq
popq %r15
popq %r14
popq %r13
popq %r12
popq %rbp
popq %rbx
ret
.size call32_from_64, .-call32_from_64
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