xref: /openbmc/linux/arch/arm/lib/backtrace.S (revision f20c7d91) 
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		bhi	for_each_frame
102
1031006:		adr	r0, .Lbad
104		mov	r1, loglvl
105		mov	r2, frame
106		bl	printk
107no_frame:	ldmfd	sp!, {r4 - r9, pc}
108ENDPROC(c_backtrace)
109
110		.pushsection __ex_table,"a"
111		.align	3
112		.long	1001b, 1006b
113		.long	1002b, 1006b
114		.long	1003b, 1006b
115		.long	1004b, 1006b
116		.popsection
117
118.Lbad:		.asciz	"%sBacktrace aborted due to bad frame pointer <%p>\n"
119		.align
120.Ldsi:		.word	0xe92dd800 >> 11	@ stmfd sp!, {... fp, ip, lr, pc}
121		.word	0xe92d0000 >> 11	@ stmfd sp!, {}
122
123#endif
124