about summary refs log tree commit diff
path: root/sysdeps/unix/sysv/linux/x86_64/getcontext.S
blob: 5ca779b15b7c6c239fdc8ff34d151b6c3158075d (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
/* Save current context.
   Copyright (C) 2002-2021 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Andreas Jaeger <aj@suse.de>, 2002.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <sysdep.h>
#include <asm/prctl.h>

#include "ucontext_i.h"

/*  int __getcontext (ucontext_t *ucp)

  Saves the machine context in UCP such that when it is activated,
  it appears as if __getcontext() returned again.

  This implementation is intended to be used for *synchronous* context
  switches only.  Therefore, it does not have to save anything
  other than the PRESERVED state.  */


ENTRY(__getcontext)
	/* Save the preserved registers, the registers used for passing
	   args, and the return address.  */
	movq	%rbx, oRBX(%rdi)
	movq	%rbp, oRBP(%rdi)
	movq	%r12, oR12(%rdi)
	movq	%r13, oR13(%rdi)
	movq	%r14, oR14(%rdi)
	movq	%r15, oR15(%rdi)

	movq	%rdi, oRDI(%rdi)
	movq	%rsi, oRSI(%rdi)
	movq	%rdx, oRDX(%rdi)
	movq	%rcx, oRCX(%rdi)
	movq	%r8, oR8(%rdi)
	movq	%r9, oR9(%rdi)

	movq	(%rsp), %rcx
	movq	%rcx, oRIP(%rdi)
	leaq	8(%rsp), %rcx		/* Exclude the return address.  */
	movq	%rcx, oRSP(%rdi)

#if SHSTK_ENABLED
	/* Check if shadow stack is enabled.  */
	testl	$X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
	jz	L(no_shstk)

	/* Save RDI in RDX which won't be clobbered by syscall.  */
	movq	%rdi, %rdx

	xorl	%eax, %eax
	cmpq	%fs:SSP_BASE_OFFSET, %rax
	jnz	L(shadow_stack_bound_recorded)

	/* Get the base address and size of the default shadow stack
	   which must be the current shadow stack since nothing has
	   been recorded yet.  */
	sub	$24, %RSP_LP
	mov	%RSP_LP, %RSI_LP
	movl	$ARCH_CET_STATUS, %edi
	movl	$__NR_arch_prctl, %eax
	syscall
	testq	%rax, %rax
	jz	L(continue_no_err)

	/* This should never happen.  */
	hlt

L(continue_no_err):
	/* Record the base of the current shadow stack.  */
	movq	8(%rsp), %rax
	movq	%rax, %fs:SSP_BASE_OFFSET
	add	$24, %RSP_LP

	/* Restore RDI.  */
	movq	%rdx, %rdi

L(shadow_stack_bound_recorded):
	/* Get the current shadow stack pointer.  */
	rdsspq	%rax
	/* NB: Save the caller's shadow stack so that we can jump back
	   to the caller directly.  */
	addq	$8, %rax
	movq	%rax, oSSP(%rdx)

	/* Save the current shadow stack base in ucontext.  */
	movq	%fs:SSP_BASE_OFFSET, %rax
	movq	%rax, (oSSP + 8)(%rdi)

L(no_shstk):
#endif
	/* We have separate floating-point register content memory on the
	   stack.  We use the __fpregs_mem block in the context.  Set the
	   links up correctly.  */

	leaq	oFPREGSMEM(%rdi), %rcx
	movq	%rcx, oFPREGS(%rdi)
	/* Save the floating-point environment.  */
	fnstenv	(%rcx)
	fldenv	(%rcx)
	stmxcsr oMXCSR(%rdi)

	/* Save the current signal mask with
	   rt_sigprocmask (SIG_BLOCK, NULL, set,_NSIG/8).  */
	leaq	oSIGMASK(%rdi), %rdx
	xorl	%esi,%esi
#if SIG_BLOCK == 0
	xorl	%edi, %edi
#else
	movl	$SIG_BLOCK, %edi
#endif
	movl	$_NSIG8,%r10d
	movl	$__NR_rt_sigprocmask, %eax
	syscall
	cmpq	$-4095, %rax		/* Check %rax for error.  */
	jae	SYSCALL_ERROR_LABEL	/* Jump to error handler if error.  */

	/* All done, return 0 for success.  */
	xorl	%eax, %eax
	ret
PSEUDO_END(__getcontext)

weak_alias (__getcontext, getcontext)