libucontext/arch/x86_64/makecontext.c

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/*
* Copyright (c) 2018 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 <stddef.h>
#include <stdarg.h>
#include <string.h>
#include <stdint.h>
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#include "defs.h"
#include <libucontext/libucontext.h>
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extern void libucontext_trampoline(void);
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_Static_assert(offsetof(libucontext_ucontext_t, uc_mcontext.gregs) == MCONTEXT_GREGS, "MCONTEXT_GREGS is invalid");
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void
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libucontext_makecontext(libucontext_ucontext_t *ucp, void (*func)(void), int argc, ...)
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{
libucontext_greg_t *sp;
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va_list va;
int i;
unsigned int uc_link;
uc_link = (argc > 6 ? argc - 6 : 0) + 1;
sp = (libucontext_greg_t *) ((uintptr_t) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
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sp -= uc_link;
sp = (libucontext_greg_t *) (((uintptr_t) sp & -16L) - 8);
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ucp->uc_mcontext.gregs[REG_RIP] = (uintptr_t) func;
ucp->uc_mcontext.gregs[REG_RBX] = (uintptr_t) &sp[uc_link];
ucp->uc_mcontext.gregs[REG_RSP] = (uintptr_t) sp;
sp[0] = (uintptr_t) &libucontext_trampoline;
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sp[uc_link] = (uintptr_t) ucp->uc_link;
va_start(va, argc);
for (i = 0; i < argc; i++)
switch (i)
{
case 0:
ucp->uc_mcontext.gregs[REG_RDI] = va_arg (va, libucontext_greg_t);
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break;
case 1:
ucp->uc_mcontext.gregs[REG_RSI] = va_arg (va, libucontext_greg_t);
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break;
case 2:
ucp->uc_mcontext.gregs[REG_RDX] = va_arg (va, libucontext_greg_t);
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break;
case 3:
ucp->uc_mcontext.gregs[REG_RCX] = va_arg (va, libucontext_greg_t);
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break;
case 4:
ucp->uc_mcontext.gregs[REG_R8] = va_arg (va, libucontext_greg_t);
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break;
case 5:
ucp->uc_mcontext.gregs[REG_R9] = va_arg (va, libucontext_greg_t);
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break;
default:
sp[i - 5] = va_arg (va, libucontext_greg_t);
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break;
}
va_end(va);
}
#ifdef EXPORT_UNPREFIXED
extern __typeof(libucontext_makecontext) makecontext __attribute__((weak, __alias__("libucontext_makecontext")));
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extern __typeof(libucontext_makecontext) __makecontext __attribute__((weak, __alias__("libucontext_makecontext")));
#endif