1/* longjmp for i386.
2   Copyright (C) 1995-2022 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 <jmpbuf-offsets.h>
21#include <jmp_buf-ssp.h>
22#include <asm-syntax.h>
23#include <stap-probe.h>
24
25/* Don't restore shadow stack register if
26   1. Shadow stack isn't enabled.  Or
27   2. __longjmp is defined for __longjmp_cancel.
28 */
29#if !SHSTK_ENABLED || defined __longjmp
30# undef SHADOW_STACK_POINTER_OFFSET
31#endif
32
33	.text
34ENTRY (__longjmp)
35#ifdef PTR_DEMANGLE
36	movl 4(%esp), %eax	/* User's jmp_buf in %eax.  */
37
38# ifdef SHADOW_STACK_POINTER_OFFSET
39#  if IS_IN (libc) && defined SHARED && defined FEATURE_1_OFFSET
40	/* Check if Shadow Stack is enabled.  */
41	testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
42	jz L(skip_ssp)
43#  else
44	xorl %edx, %edx
45#  endif
46	/* Check and adjust the Shadow-Stack-Pointer.  */
47	rdsspd %edx
48	/* And compare it with the saved ssp value.  */
49	subl SHADOW_STACK_POINTER_OFFSET(%eax), %edx
50	je L(skip_ssp)
51	/* Count the number of frames to adjust and adjust it
52	   with incssp instruction.  The instruction can adjust
53	   the ssp by [0..255] value only thus use a loop if
54	   the number of frames is bigger than 255.  */
55	negl %edx
56	shrl $2, %edx
57	/* NB: We saved Shadow-Stack-Pointer of setjmp.  Since we are
58	       restoring Shadow-Stack-Pointer of setjmp's caller, we
59	       need to unwind shadow stack by one more frame.  */
60	addl $1, %edx
61	movl	$255, %ebx
62L(loop):
63	cmpl	%ebx, %edx
64	cmovb	%edx, %ebx
65	incsspd	%ebx
66	subl	%ebx, %edx
67	ja	L(loop)
68L(skip_ssp):
69# endif
70	/* Save the return address now.  */
71	movl (JB_PC*4)(%eax), %edx
72	/* Get the stack pointer.  */
73	movl (JB_SP*4)(%eax), %ecx
74	PTR_DEMANGLE (%edx)
75	PTR_DEMANGLE (%ecx)
76	LIBC_PROBE (longjmp, 3, 4@%eax, -4@8(%esp), 4@%edx)
77	cfi_def_cfa(%eax, 0)
78	cfi_register(%eip, %edx)
79	cfi_register(%esp, %ecx)
80	cfi_offset(%ebx, JB_BX*4)
81	cfi_offset(%esi, JB_SI*4)
82	cfi_offset(%edi, JB_DI*4)
83	cfi_offset(%ebp, JB_BP*4)
84	/* Restore registers.  */
85	movl (JB_BX*4)(%eax), %ebx
86	movl (JB_SI*4)(%eax), %esi
87	movl (JB_DI*4)(%eax), %edi
88	movl (JB_BP*4)(%eax), %ebp
89	cfi_restore(%ebx)
90	cfi_restore(%esi)
91	cfi_restore(%edi)
92	cfi_restore(%ebp)
93
94	LIBC_PROBE (longjmp_target, 3, 4@%eax, -4@8(%esp), 4@%edx)
95	movl 8(%esp), %eax	/* Second argument is return value.  */
96	movl %ecx, %esp
97#else
98	movl 4(%esp), %ecx	/* User's jmp_buf in %ecx.  */
99	movl 8(%esp), %eax	/* Second argument is return value.  */
100# ifdef SHADOW_STACK_POINTER_OFFSET
101#  if IS_IN (libc) && defined SHARED
102	/* Check if Shadow Stack is enabled.  */
103	testl $X86_FEATURE_1_SHSTK, %gs:FEATURE_1_OFFSET
104	jz L(skip_ssp)
105#  endif
106	/* Check and adjust the Shadow-Stack-Pointer.  */
107	xorl %edx, %edx
108	/* Get the current ssp.  */
109	rdsspd	%edx
110	/* And compare it with the saved ssp value.  */
111	subl SHADOW_STACK_POINTER_OFFSET(%ecx), %edx
112	je L(skip_ssp)
113	/* Count the number of frames to adjust and adjust it
114	   with incssp instruction.  The instruction can adjust
115	   the ssp by [0..255] value only thus use a loop if
116	   the number of frames is bigger than 255.  */
117	negl %edx
118	shrl $2, %edx
119	/* NB: We saved Shadow-Stack-Pointer of setjmp.  Since we are
120	       restoring Shadow-Stack-Pointer of setjmp's caller, we
121	       need to unwind shadow stack by one more frame.  */
122	addl $1, %edx
123	movl	$255, %ebx
124L(loop):
125	cmpl	%ebx, %edx
126	cmovb	%edx, %ebx
127	incsspd	%ebx
128	subl	%ebx, %edx
129	ja	L(loop)
130L(skip_ssp):
131# endif
132	/* Save the return address now.  */
133	movl (JB_PC*4)(%ecx), %edx
134	LIBC_PROBE (longjmp, 3, 4@%ecx, -4@%eax, 4@%edx)
135	/* Restore registers.  */
136	movl (JB_BX*4)(%ecx), %ebx
137	movl (JB_SI*4)(%ecx), %esi
138	movl (JB_DI*4)(%ecx), %edi
139	movl (JB_BP*4)(%ecx), %ebp
140	movl (JB_SP*4)(%ecx), %esp
141	LIBC_PROBE (longjmp_target, 3, 4@%ecx, -4@%ecx, 4@%edx)
142#endif
143	/* Jump to saved PC.  */
144	jmp *%edx
145END (__longjmp)
146