libucontext/arch/x86/getcontext.S

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/*
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* Copyright (c) 2018, 2020 Ariadne Conill <ariadne@dereferenced.org>
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*
* 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.
*/
#include "defs.h"
ALIAS(getcontext, libucontext_getcontext)
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ALIAS(__getcontext, libucontext_getcontext)
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FUNC(libucontext_getcontext)
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/* load address of the ucontext structure */
movl 4(%esp), %eax
/* EAX is not a preserved register */
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movl $0, REG_OFFSET(REG_EAX)(%eax)
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/* copy all of the current registers into the ucontext structure */
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movl %ecx, REG_OFFSET(REG_ECX)(%eax)
movl %ebx, REG_OFFSET(REG_EBX)(%eax)
movl %edx, REG_OFFSET(REG_EDX)(%eax)
movl %edi, REG_OFFSET(REG_EDI)(%eax)
movl %esi, REG_OFFSET(REG_ESI)(%eax)
movl %ebp, REG_OFFSET(REG_EBP)(%eax)
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/* the first argument on the stack is the jump target (%eip), so we store it in the EIP
register in the ucontext structure. */
movl (%esp), %ecx
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movl %ecx, REG_OFFSET(REG_EIP)(%eax)
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/* take the stack pointer address (%esp) offsetting by 4 to skip over the jump target. */
leal 4(%esp), %ecx
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movl %ecx, REG_OFFSET(REG_ESP)(%eax)
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/* finally, save the FS segment register */
xorl %ecx, %ecx
movw %fs, %cx
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movl %ecx, REG_OFFSET(REG_FS)(%eax)
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/* we're all done here, return 0 */
xorl %eax, %eax
ret
END(libucontext_getcontext)