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80 lines
2.4 KiB
C
80 lines
2.4 KiB
C
/* Create new context.
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Copyright (C) 2015-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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#include <stdarg.h>
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#include <stdint.h>
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#include <ucontext.h>
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/* makecontext sets up a stack and the registers for the
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user context. The stack looks like this:
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+-----------------------+
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| padding as required |
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+-----------------------+
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sp -> | parameters 5 to n |
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+-----------------------+
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The registers are set up like this:
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r4--r7 : parameter 1 to 4
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r16 : uc_link
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sp : stack pointer.
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*/
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void
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__makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
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{
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extern void __startcontext (void);
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unsigned long *sp;
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va_list ap;
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int i;
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sp = (unsigned long *)
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((uintptr_t) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
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/* Allocate stack arguments. */
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sp -= argc < 4 ? 0 : argc - 4;
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/* Keep the stack aligned. */
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sp = (unsigned long*) (((uintptr_t) sp) & -4L);
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/* Init version field. */
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ucp->uc_mcontext.version = 2;
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/* Keep uc_link in r16. */
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ucp->uc_mcontext.regs[15] = (uintptr_t) ucp->uc_link;
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/* Return address points to __startcontext(). */
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ucp->uc_mcontext.regs[23] = (uintptr_t) &__startcontext;
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/* Frame pointer is null. */
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ucp->uc_mcontext.regs[24] = (uintptr_t) 0;
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/* Restart in user-space starting at 'func'. */
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ucp->uc_mcontext.regs[27] = (uintptr_t) func;
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/* Set stack pointer. */
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ucp->uc_mcontext.regs[28] = (uintptr_t) sp;
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va_start (ap, argc);
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for (i = 0; i < argc; ++i)
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if (i < 4)
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ucp->uc_mcontext.regs[i + 3] = va_arg (ap, unsigned long);
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else
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sp[i - 4] = va_arg (ap, unsigned long);
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va_end (ap);
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}
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weak_alias (__makecontext, makecontext)
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