1/* Save current context.
2   Copyright (C) 2002-2022 Free Software Foundation, Inc.
3   This file is part of the GNU C Library.
4
5   The GNU C Library is free software; you can redistribute it and/or
6   modify it under the terms of the GNU Lesser General Public
7   License as published by the Free Software Foundation; either
8   version 2.1 of the License, or (at your option) any later version.
9
10   The GNU C Library is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13   Lesser General Public License for more details.
14
15   You should have received a copy of the GNU Lesser General Public
16   License along with the GNU C Library; if not, see
17   <https://www.gnu.org/licenses/>.  */
18
19#include <sysdep.h>
20#include <asm/prctl.h>
21
22#include "ucontext_i.h"
23
24/*  int __getcontext (ucontext_t *ucp)
25
26  Saves the machine context in UCP such that when it is activated,
27  it appears as if __getcontext() returned again.
28
29  This implementation is intended to be used for *synchronous* context
30  switches only.  Therefore, it does not have to save anything
31  other than the PRESERVED state.  */
32
33
34ENTRY(__getcontext)
35	/* Save the preserved registers, the registers used for passing
36	   args, and the return address.  */
37	movq	%rbx, oRBX(%rdi)
38	movq	%rbp, oRBP(%rdi)
39	movq	%r12, oR12(%rdi)
40	movq	%r13, oR13(%rdi)
41	movq	%r14, oR14(%rdi)
42	movq	%r15, oR15(%rdi)
43
44	movq	%rdi, oRDI(%rdi)
45	movq	%rsi, oRSI(%rdi)
46	movq	%rdx, oRDX(%rdi)
47	movq	%rcx, oRCX(%rdi)
48	movq	%r8, oR8(%rdi)
49	movq	%r9, oR9(%rdi)
50
51	movq	(%rsp), %rcx
52	movq	%rcx, oRIP(%rdi)
53	leaq	8(%rsp), %rcx		/* Exclude the return address.  */
54	movq	%rcx, oRSP(%rdi)
55
56#if SHSTK_ENABLED
57	/* Check if shadow stack is enabled.  */
58	testl	$X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET
59	jz	L(no_shstk)
60
61	/* Save RDI in RDX which won't be clobbered by syscall.  */
62	movq	%rdi, %rdx
63
64	xorl	%eax, %eax
65	cmpq	%fs:SSP_BASE_OFFSET, %rax
66	jnz	L(shadow_stack_bound_recorded)
67
68	/* Get the base address and size of the default shadow stack
69	   which must be the current shadow stack since nothing has
70	   been recorded yet.  */
71	sub	$24, %RSP_LP
72	mov	%RSP_LP, %RSI_LP
73	movl	$ARCH_CET_STATUS, %edi
74	movl	$__NR_arch_prctl, %eax
75	syscall
76	testq	%rax, %rax
77	jz	L(continue_no_err)
78
79	/* This should never happen.  */
80	hlt
81
82L(continue_no_err):
83	/* Record the base of the current shadow stack.  */
84	movq	8(%rsp), %rax
85	movq	%rax, %fs:SSP_BASE_OFFSET
86	add	$24, %RSP_LP
87
88	/* Restore RDI.  */
89	movq	%rdx, %rdi
90
91L(shadow_stack_bound_recorded):
92	/* Get the current shadow stack pointer.  */
93	rdsspq	%rax
94	/* NB: Save the caller's shadow stack so that we can jump back
95	   to the caller directly.  */
96	addq	$8, %rax
97	movq	%rax, oSSP(%rdx)
98
99	/* Save the current shadow stack base in ucontext.  */
100	movq	%fs:SSP_BASE_OFFSET, %rax
101	movq	%rax, (oSSP + 8)(%rdi)
102
103L(no_shstk):
104#endif
105	/* We have separate floating-point register content memory on the
106	   stack.  We use the __fpregs_mem block in the context.  Set the
107	   links up correctly.  */
108
109	leaq	oFPREGSMEM(%rdi), %rcx
110	movq	%rcx, oFPREGS(%rdi)
111	/* Save the floating-point environment.  */
112	fnstenv	(%rcx)
113	fldenv	(%rcx)
114	stmxcsr oMXCSR(%rdi)
115
116	/* Save the current signal mask with
117	   rt_sigprocmask (SIG_BLOCK, NULL, set,_NSIG/8).  */
118	leaq	oSIGMASK(%rdi), %rdx
119	xorl	%esi,%esi
120#if SIG_BLOCK == 0
121	xorl	%edi, %edi
122#else
123	movl	$SIG_BLOCK, %edi
124#endif
125	movl	$_NSIG8,%r10d
126	movl	$__NR_rt_sigprocmask, %eax
127	syscall
128	cmpq	$-4095, %rax		/* Check %rax for error.  */
129	jae	SYSCALL_ERROR_LABEL	/* Jump to error handler if error.  */
130
131	/* All done, return 0 for success.  */
132	xorl	%eax, %eax
133	ret
134PSEUDO_END(__getcontext)
135
136weak_alias (__getcontext, getcontext)
137