1/* Save current context.
2   Copyright (C) 2001-2022 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
25ENTRY(__getcontext)
26	/* Load address of the context data structure.  */
27	movl	4(%esp), %eax
28
29	/* Save the preserved register values and the return address.  */
30	movl	%edi, oEDI(%eax)
31	movl	%esi, oESI(%eax)
32	movl	%ebp, oEBP(%eax)
33	movl	(%esp), %ecx
34	movl	%ecx, oEIP(%eax)
35	leal	4(%esp), %ecx		/* Exclude the return address.  */
36	movl	%ecx, oESP(%eax)
37	movl	%ebx, oEBX(%eax)
38
39	/* Save the FS segment register.  We don't touch the GS register
40	   since it is used for threads.  */
41	xorl	%edx, %edx
42	movw	%fs, %dx
43	movl	%edx, oFS(%eax)
44
45#if SHSTK_ENABLED
46	/* Check if shadow stack is enabled.  */
47	testl	$X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
48	jz	L(no_shstk)
49
50	/* Save EAX in EDX.  */
51	movl	%eax, %edx
52
53	xorl	%eax, %eax
54	cmpl	%gs:SSP_BASE_OFFSET, %eax
55	jnz	L(shadow_stack_bound_recorded)
56
57	/* Save EBX in the first scratch register slot.  */
58	movl	%ebx, oSCRATCH1(%edx)
59
60	/* Get the base address and size of the default shadow stack
61	   which must be the current shadow stack since nothing has
62	   been recorded yet.  */
63	sub	$24, %esp
64	mov	%esp, %ecx
65	movl	$ARCH_CET_STATUS, %ebx
66	movl	$__NR_arch_prctl, %eax
67	ENTER_KERNEL
68	testl	%eax, %eax
69	jz	L(continue_no_err)
70
71	/* This should never happen.  */
72	hlt
73
74L(continue_no_err):
75	/* Restore EBX from the first scratch register slot.  */
76	movl	oSCRATCH1(%edx), %ebx
77
78	/* Record the base of the current shadow stack.  */
79	movl	8(%esp), %eax
80	movl	%eax, %gs:SSP_BASE_OFFSET
81	add	$24, %esp
82
83L(shadow_stack_bound_recorded):
84	/* Load address of the context data structure.  */
85	movl	4(%esp), %eax
86
87	/* Get the current shadow stack pointer.  */
88	rdsspd	%edx
89	/* NB: Save the caller's shadow stack so that we can jump back
90	   to the caller directly.  */
91	addl	$4, %edx
92	movl	%edx, oSSP(%eax)
93
94	/* Save the current shadow stack base in ucontext.  */
95	movl	%gs:SSP_BASE_OFFSET, %edx
96	movl	%edx, (oSSP + 4)(%eax)
97
98L(no_shstk):
99#endif
100	/* We have separate floating-point register content memory on the
101	   stack.  We use the __fpregs_mem block in the context.  Set the
102	   links up correctly.  */
103	leal	oFPREGSMEM(%eax), %ecx
104	movl	%ecx, oFPREGS(%eax)
105	/* Save the floating-point context.  */
106	fnstenv	(%ecx)
107	/* And load it right back since the processor changes the mask.
108	   Intel thought this opcode to be used in interrupt handlers which
109	   would block all exceptions.  */
110	fldenv	(%ecx)
111
112	/* Save the current signal mask.  */
113	pushl	%ebx
114	cfi_adjust_cfa_offset (4)
115	cfi_rel_offset (ebx, 0)
116	leal	oSIGMASK(%eax), %edx
117	xorl	%ecx, %ecx
118	movl	$SIG_BLOCK, %ebx
119	movl	$__NR_sigprocmask, %eax
120	ENTER_KERNEL
121	popl	%ebx
122	cfi_adjust_cfa_offset (-4)
123	cfi_restore (ebx)
124	cmpl	$-4095, %eax		/* Check %eax for error.  */
125	jae	SYSCALL_ERROR_LABEL	/* Jump to error handler if error.  */
126
127	/* All done, return 0 for success.  */
128	xorl	%eax, %eax
129	ret
130PSEUDO_END(__getcontext)
131
132weak_alias (__getcontext, getcontext)
133