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1/* SPDX-License-Identifier: GPL-2.0-only */
2/*
3 * linux/arch/arm/lib/backtrace.S
4 *
5 * Copyright (C) 1995, 1996 Russell King
6 *
7 * 27/03/03 Ian Molton Clean up CONFIG_CPU
8 */
9#include <linux/kern_levels.h>
10#include <linux/linkage.h>
11#include <asm/assembler.h>
12 .text
13
14@ fp is 0 or stack frame
15
16#define frame r4
17#define sv_fp r5
18#define sv_pc r6
19#define mask r7
20#define offset r8
21#define loglvl r9
22
23ENTRY(c_backtrace)
24
25#if !defined(CONFIG_FRAME_POINTER) || !defined(CONFIG_PRINTK)
26 ret lr
27ENDPROC(c_backtrace)
28#else
29 stmfd sp!, {r4 - r9, lr} @ Save an extra register so we have a location...
30 movs frame, r0 @ if frame pointer is zero
31 beq no_frame @ we have no stack frames
32 mov loglvl, r2
33
34 tst r1, #0x10 @ 26 or 32-bit mode?
35 ARM( moveq mask, #0xfc000003 )
36 THUMB( moveq mask, #0xfc000000 )
37 THUMB( orreq mask, #0x03 )
38 movne mask, #0 @ mask for 32-bit
39
401: stmfd sp!, {pc} @ calculate offset of PC stored
41 ldr r0, [sp], #4 @ by stmfd for this CPU
42 adr r1, 1b
43 sub offset, r0, r1
44
45/*
46 * Stack frame layout:
47 * optionally saved caller registers (r4 - r10)
48 * saved fp
49 * saved sp
50 * saved lr
51 * frame => saved pc
52 * optionally saved arguments (r0 - r3)
53 * saved sp => <next word>
54 *
55 * Functions start with the following code sequence:
56 * mov ip, sp
57 * stmfd sp!, {r0 - r3} (optional)
58 * corrected pc => stmfd sp!, {..., fp, ip, lr, pc}
59 */
60for_each_frame: tst frame, mask @ Check for address exceptions
61 bne no_frame
62
631001: ldr sv_pc, [frame, #0] @ get saved pc
641002: ldr sv_fp, [frame, #-12] @ get saved fp
65
66 sub sv_pc, sv_pc, offset @ Correct PC for prefetching
67 bic sv_pc, sv_pc, mask @ mask PC/LR for the mode
68
691003: ldr r2, [sv_pc, #-4] @ if stmfd sp!, {args} exists,
70 ldr r3, .Ldsi+4 @ adjust saved 'pc' back one
71 teq r3, r2, lsr #11 @ instruction
72 subne r0, sv_pc, #4 @ allow for mov
73 subeq r0, sv_pc, #8 @ allow for mov + stmia
74
75 ldr r1, [frame, #-4] @ get saved lr
76 mov r2, frame
77 bic r1, r1, mask @ mask PC/LR for the mode
78 mov r3, loglvl
79 bl dump_backtrace_entry
80
81 ldr r1, [sv_pc, #-4] @ if stmfd sp!, {args} exists,
82 ldr r3, .Ldsi+4
83 teq r3, r1, lsr #11
84 ldreq r0, [frame, #-8] @ get sp
85 subeq r0, r0, #4 @ point at the last arg
86 mov r2, loglvl
87 bleq dump_backtrace_stm @ dump saved registers
88
891004: ldr r1, [sv_pc, #0] @ if stmfd sp!, {..., fp, ip, lr, pc}
90 ldr r3, .Ldsi @ instruction exists,
91 teq r3, r1, lsr #11
92 subeq r0, frame, #16
93 mov r2, loglvl
94 bleq dump_backtrace_stm @ dump saved registers
95
96 teq sv_fp, #0 @ zero saved fp means
97 beq no_frame @ no further frames
98
99 cmp sv_fp, frame @ next frame must be
100 mov frame, sv_fp @ above the current frame
101#ifdef CONFIG_IRQSTACKS
102 @
103 @ Kernel stacks may be discontiguous in memory. If the next
104 @ frame is below the previous frame, accept it as long as it
105 @ lives in kernel memory.
106 @
107 cmpls sv_fp, #PAGE_OFFSET
108#endif
109 bhi for_each_frame
110
1111006: adr r0, .Lbad
112 mov r1, loglvl
113 mov r2, frame
114 bl _printk
115no_frame: ldmfd sp!, {r4 - r9, pc}
116ENDPROC(c_backtrace)
117
118 .pushsection __ex_table,"a"
119 .align 3
120 .long 1001b, 1006b
121 .long 1002b, 1006b
122 .long 1003b, 1006b
123 .long 1004b, 1006b
124 .popsection
125
126.Lbad: .asciz "%sBacktrace aborted due to bad frame pointer <%p>\n"
127 .align
128.Ldsi: .word 0xe92dd800 >> 11 @ stmfd sp!, {... fp, ip, lr, pc}
129 .word 0xe92d0000 >> 11 @ stmfd sp!, {}
130
131#endif