libucontext/arch/x86_64/swapcontext.S

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2018-01-30 03:41:02 +00:00
/*
* Copyright (c) 2018 William Pitcock <nenolod@dereferenced.org>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* This software is provided 'as is' and without any warranty, express or
* implied. In no event shall the authors be liable for any damages arising
* from the use of this software.
*/
.globl __swapcontext;
__swapcontext:
/* copy all of the current registers into the ucontext structure pointed by
the first argument */
movq %r8, 40(%rdi)
movq %r9, 48(%rdi)
movq %r10, 56(%rdi)
movq %r11, 64(%rdi)
movq %r12, 72(%rdi)
movq %r13, 80(%rdi)
movq %r14, 88(%rdi)
movq %r15, 96(%rdi)
movq %rdi, 104(%rdi)
movq %rbp, 112(%rdi)
movq %rsi, 120(%rdi)
movq %rbx, 128(%rdi)
movq %rdx, 136(%rdi)
movq $1, 144(%rdi) /* $1 is %rax */
movq %rcx, 152(%rdi)
/* the first argument on the stack is the jump target (%rip), so we store it in the RIP
register in the ucontext structure. */
movq (%rsp), %rcx
movq %rcx, 168(%rdi)
/* finally take the stack pointer address (%rsp) offsetting by 8 to skip over the jump
target. */
leaq 8(%rsp), %rcx
movq %rcx, 160(%rdi)
/* set all of the registers to their new states, stored in the second
ucontext structure */
movq 40(%rsi), %r8
movq 48(%rsi), %r9
movq 56(%rsi), %r10
movq 64(%rsi), %r11
movq 72(%rsi), %r12
movq 80(%rsi), %r13
movq 88(%rsi), %r14
movq 96(%rsi), %r15
movq 104(%rsi), %rdi
movq 112(%rsi), %rbp
movq 128(%rsi), %rbx
movq 136(%rsi), %rdx
movq 144(%rsi), %rax
movq 152(%rsi), %rcx
movq 160(%rsi), %rsp
/* set the jump target by pushing it to the stack.
ret will pop the new %rip from the stack, causing us to jump there. */
pushq 168(%rsi)
/* finally, set %rsi correctly since we do not need it anymore. */
movq 120(%rsi), %rsi
/* we're all done here, return 0 */
xorl %eax, %eax
ret
.weak swapcontext;
swapcontext = __swapcontext;