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5d844e1b72
1. getcontext and swapcontext are updated to save the caller's shadow stack pointer and return address. 2. setcontext and swapcontext are updated to restore shadow stack and jump to new context directly. 3. makecontext is updated to allocate a new shadow stack and set the caller's return address to the helper code, L(exitcode). 4. Since we no longer save and restore EAX, ECX and EDX in getcontext, setcontext and swapcontext, we can use them as scratch register slots to enable CET in ucontext functions. Since makecontext allocates a new shadow stack when making a new context and kernel allocates a new shadow stack for clone/fork/vfork syscalls, we track the current shadow stack base. In setcontext and swapcontext, if the target shadow stack base is the same as the current shadow stack base, we unwind the shadow stack. Otherwise it is a stack switch and we look for a restore token. We enable shadow stack at run-time only if program and all used shared objects, including dlopened ones, are shadow stack enabled, which means that they must be compiled with GCC 8 or above and glibc 2.28 or above. We need to save and restore shadow stack only if shadow stack is enabled. When caller of getcontext, setcontext, swapcontext and makecontext is compiled with smaller ucontext_t, shadow stack won't be enabled at run-time. We check if shadow stack is enabled before accessing the extended field in ucontext_t. Tested on i386 CET/non-CET machines. Reviewed-by: Carlos O'Donell <carlos@redhat.com>
254 lines
6.7 KiB
ArmAsm
254 lines
6.7 KiB
ArmAsm
/* Create new context.
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Copyright (C) 2001-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2001.
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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 <asm/prctl.h>
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#include "ucontext_i.h"
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ENTRY(__makecontext)
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movl 4(%esp), %eax
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/* Load the address of the function we are supposed to run. */
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movl 8(%esp), %ecx
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/* Compute the address of the stack. The information comes from
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to us_stack element. */
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movl oSS_SP(%eax), %edx
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movl %ecx, oEIP(%eax)
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addl oSS_SIZE(%eax), %edx
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/* Remember the number of parameters for the exit handler since
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it has to remove them. We store the number in the EBX register
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which the function we will call must preserve. */
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movl 12(%esp), %ecx
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movl %ecx, oEBX(%eax)
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/* Make room on the new stack for the parameters.
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Room for the arguments, return address (== L(exitcode)) and
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oLINK pointer is needed. One of the pointer sizes is subtracted
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after aligning the stack. */
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negl %ecx
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leal -4(%edx,%ecx,4), %edx
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negl %ecx
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/* Align the stack. */
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andl $0xfffffff0, %edx
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subl $4, %edx
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/* Store the future stack pointer. */
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movl %edx, oESP(%eax)
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/* Put the next context on the new stack (from the uc_link
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element). */
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movl oLINK(%eax), %eax
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movl %eax, 4(%edx,%ecx,4)
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/* Copy all the parameters. */
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jecxz 2f
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1: movl 12(%esp,%ecx,4), %eax
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movl %eax, (%edx,%ecx,4)
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decl %ecx
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jnz 1b
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2:
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#if SHSTK_ENABLED
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/* Check if Shadow Stack is enabled. */
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testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
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jz L(skip_ssp)
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/* Reload the pointer to ucontext. */
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movl 4(%esp), %eax
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/* Shadow stack is enabled. We need to allocate a new shadow
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stack. */
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subl oSS_SP(%eax), %edx
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shrl $STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT, %edx
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/* Align shadow stack size to 8 bytes. */
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addl $7, %edx
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andl $-8, %edx
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/* Store shadow stack size in __ssp[2]. */
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movl %edx, (oSSP + 8)(%eax)
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/* Save ESI in the second scratch register slot. */
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movl %esi, oSCRATCH2(%eax)
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/* Save EDI in the third scratch register slot. */
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movl %edi, oSCRATCH3(%eax)
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/* Save the pointer to ucontext. */
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movl %eax, %edi
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/* Get the original shadow stack pointer. */
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rdsspd %esi
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/* Align the saved original shadow stack pointer to the next
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8 byte aligned boundary. */
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andl $-8, %esi
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/* Load the top of the new stack into EDX. */
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movl oESP(%eax), %edx
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/* We need to terminate the FDE here because the unwinder looks
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at ra-1 for unwind information. */
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cfi_endproc
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/* Swap the original stack pointer with the top of the new
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stack. */
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xchgl %esp, %edx
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/* Add 4 bytes since CALL will push the 4-byte return address
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onto stack. */
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addl $4, %esp
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/* Allocate the new shadow stack. Save EBX in the first scratch
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register slot. */
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movl %ebx, oSCRATCH1(%eax)
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/* CET syscall takes 64-bit sizes. */
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subl $16, %esp
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movl (oSSP + 8)(%eax), %ecx
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movl %ecx, (%esp)
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movl $0, 4(%esp)
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movl %ecx, 8(%esp)
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movl $0, 12(%esp)
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movl %esp, %ecx
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movl $ARCH_CET_ALLOC_SHSTK, %ebx
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movl $__NR_arch_prctl, %eax
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ENTER_KERNEL
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testl %eax, %eax
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jne L(hlt) /* This should never happen. */
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/* Copy the base address of the new shadow stack to __ssp[1]. */
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movl (%esp), %eax
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movl %eax, (oSSP + 4)(%edi)
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addl $16, %esp
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/* Restore EBX from the first scratch register slot. */
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movl oSCRATCH1(%edi), %ebx
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/* Get the size of the new shadow stack. */
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movl (oSSP + 8)(%edi), %ecx
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/* Use the restore stoken to restore the new shadow stack. */
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rstorssp -8(%eax, %ecx)
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/* Save the restore token at the next 8 byte aligned boundary
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on the original shadow stack. */
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saveprevssp
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/* Push the address of "jmp exitcode" onto the new stack as
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well as the new shadow stack. */
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call 1f
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jmp L(exitcode)
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1:
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/* Get the new shadow stack pointer. */
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rdsspd %eax
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/* Use the restore stoken to restore the original shadow stack. */
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rstorssp -8(%esi)
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/* Save the restore token on the new shadow stack. */
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saveprevssp
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/* Store the new shadow stack pointer in __ssp[0]. */
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movl %eax, oSSP(%edi)
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/* Restore the original stack. */
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mov %edx, %esp
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cfi_startproc
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/* Restore ESI from the second scratch register slot. */
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movl oSCRATCH2(%edi), %esi
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/* Restore EDI from the third scratch register slot. */
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movl oSCRATCH3(%edi), %edi
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ret
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L(skip_ssp):
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#endif
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/* If the function we call returns we must continue with the
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context which is given in the uc_link element. To do this
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set the return address for the function the user provides
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to a little bit of helper code which does the magic (see
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below). */
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#ifdef PIC
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call 1f
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cfi_adjust_cfa_offset (4)
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1: popl %ecx
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cfi_adjust_cfa_offset (-4)
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addl $L(exitcode)-1b, %ecx
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movl %ecx, (%edx)
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#else
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movl $L(exitcode), (%edx)
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#endif
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/* We need to terminate the FDE here instead of after ret because
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the unwinder looks at ra-1 for unwind information. */
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cfi_endproc
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/* 'makecontext' returns no value. */
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ret
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/* This is the helper code which gets called if a function which
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is registered with 'makecontext' returns. In this case we
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have to install the context listed in the uc_link element of
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the context 'makecontext' manipulated at the time of the
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'makecontext' call. If the pointer is NULL the process must
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terminate. */
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L(exitcode):
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/* This removes the parameters passed to the function given to
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'makecontext' from the stack. EBX contains the number of
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parameters (see above). */
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leal (%esp,%ebx,4), %esp
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cmpl $0, (%esp) /* Check the next context. */
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je 2f /* If it is zero exit. */
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call HIDDEN_JUMPTARGET(__setcontext)
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/* If this returns (which can happen if the syscall fails) we'll
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exit the program with the return error value (-1). */
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jmp L(call_exit)
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2:
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/* Exit with status 0. */
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xorl %eax, %eax
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L(call_exit):
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/* Align the stack and pass the exit code (from %eax). */
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andl $0xfffffff0, %esp
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subl $12, %esp
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pushl %eax
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call HIDDEN_JUMPTARGET(exit)
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/* The 'exit' call should never return. In case it does cause
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the process to terminate. */
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L(hlt):
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hlt
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cfi_startproc
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END(__makecontext)
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weak_alias (__makecontext, makecontext)
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