1/* Save current context.
2 Copyright (C) 2002-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Andreas Jaeger <aj@suse.de>, 2002.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20#include <sysdep.h>
21#include <asm/prctl.h>
22
23#include "ucontext_i.h"
24
25/* int __getcontext (ucontext_t *ucp)
26
27 Saves the machine context in UCP such that when it is activated,
28 it appears as if __getcontext() returned again.
29
30 This implementation is intended to be used for *synchronous* context
31 switches only. Therefore, it does not have to save anything
32 other than the PRESERVED state. */
33
34
35ENTRY(__getcontext)
36 /* Save the preserved registers, the registers used for passing
37 args, and the return address. */
38 movq %rbx, oRBX(%rdi)
39 movq %rbp, oRBP(%rdi)
40 movq %r12, oR12(%rdi)
41 movq %r13, oR13(%rdi)
42 movq %r14, oR14(%rdi)
43 movq %r15, oR15(%rdi)
44
45 movq %rdi, oRDI(%rdi)
46 movq %rsi, oRSI(%rdi)
47 movq %rdx, oRDX(%rdi)
48 movq %rcx, oRCX(%rdi)
49 movq %r8, oR8(%rdi)
50 movq %r9, oR9(%rdi)
51
52 movq (%rsp), %rcx
53 movq %rcx, oRIP(%rdi)
54 leaq 8(%rsp), %rcx /* Exclude the return address. */
55 movq %rcx, oRSP(%rdi)
56
57#if SHSTK_ENABLED
58 /* Check if shadow stack is enabled. */
59 testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
60 jz L(no_shstk)
61
62 /* Save RDI in RDX which won't be clobbered by syscall. */
63 movq %rdi, %rdx
64
65 xorl %eax, %eax
66 cmpq %fs:SSP_BASE_OFFSET, %rax
67 jnz L(shadow_stack_bound_recorded)
68
69 /* Get the base address and size of the default shadow stack
70 which must be the current shadow stack since nothing has
71 been recorded yet. */
72 sub $24, %RSP_LP
73 mov %RSP_LP, %RSI_LP
74 movl $ARCH_CET_STATUS, %edi
75 movl $__NR_arch_prctl, %eax
76 syscall
77 testq %rax, %rax
78 jz L(continue_no_err)
79
80 /* This should never happen. */
81 hlt
82
83L(continue_no_err):
84 /* Record the base of the current shadow stack. */
85 movq 8(%rsp), %rax
86 movq %rax, %fs:SSP_BASE_OFFSET
87 add $24, %RSP_LP
88
89 /* Restore RDI. */
90 movq %rdx, %rdi
91
92L(shadow_stack_bound_recorded):
93 /* Get the current shadow stack pointer. */
94 rdsspq %rax
95 /* NB: Save the caller's shadow stack so that we can jump back
96 to the caller directly. */
97 addq $8, %rax
98 movq %rax, oSSP(%rdx)
99
100 /* Save the current shadow stack base in ucontext. */
101 movq %fs:SSP_BASE_OFFSET, %rax
102 movq %rax, (oSSP + 8)(%rdi)
103
104L(no_shstk):
105#endif
106 /* We have separate floating-point register content memory on the
107 stack. We use the __fpregs_mem block in the context. Set the
108 links up correctly. */
109
110 leaq oFPREGSMEM(%rdi), %rcx
111 movq %rcx, oFPREGS(%rdi)
112 /* Save the floating-point environment. */
113 fnstenv (%rcx)
114 fldenv (%rcx)
115 stmxcsr oMXCSR(%rdi)
116
117 /* Save the current signal mask with
118 rt_sigprocmask (SIG_BLOCK, NULL, set,_NSIG/8). */
119 leaq oSIGMASK(%rdi), %rdx
120 xorl %esi,%esi
121#if SIG_BLOCK == 0
122 xorl %edi, %edi
123#else
124 movl $SIG_BLOCK, %edi
125#endif
126 movl $_NSIG8,%r10d
127 movl $__NR_rt_sigprocmask, %eax
128 syscall
129 cmpq $-4095, %rax /* Check %rax for error. */
130 jae SYSCALL_ERROR_LABEL /* Jump to error handler if error. */
131
132 /* All done, return 0 for success. */
133 xorl %eax, %eax
134 ret
135PSEUDO_END(__getcontext)
136
137weak_alias (__getcontext, getcontext)
138