xref: /openbmc/linux/arch/arm/lib/backtrace.S (revision aa5b395b) 
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
22ENTRY(c_backtrace)
23
24#if !defined(CONFIG_FRAME_POINTER) || !defined(CONFIG_PRINTK)
25		ret	lr
26ENDPROC(c_backtrace)
27#else
28		stmfd	sp!, {r4 - r8, lr}	@ Save an extra register so we have a location...
29		movs	frame, r0		@ if frame pointer is zero
30		beq	no_frame		@ we have no stack frames
31
32		tst	r1, #0x10		@ 26 or 32-bit mode?
33 ARM(		moveq	mask, #0xfc000003	)
34 THUMB(		moveq	mask, #0xfc000000	)
35 THUMB(		orreq	mask, #0x03		)
36		movne	mask, #0		@ mask for 32-bit
37
381:		stmfd	sp!, {pc}		@ calculate offset of PC stored
39		ldr	r0, [sp], #4		@ by stmfd for this CPU
40		adr	r1, 1b
41		sub	offset, r0, r1
42
43/*
44 * Stack frame layout:
45 *             optionally saved caller registers (r4 - r10)
46 *             saved fp
47 *             saved sp
48 *             saved lr
49 *    frame => saved pc
50 *             optionally saved arguments (r0 - r3)
51 * saved sp => <next word>
52 *
53 * Functions start with the following code sequence:
54 *                  mov   ip, sp
55 *                  stmfd sp!, {r0 - r3} (optional)
56 * corrected pc =>  stmfd sp!, {..., fp, ip, lr, pc}
57 */
58for_each_frame:	tst	frame, mask		@ Check for address exceptions
59		bne	no_frame
60
611001:		ldr	sv_pc, [frame, #0]	@ get saved pc
621002:		ldr	sv_fp, [frame, #-12]	@ get saved fp
63
64		sub	sv_pc, sv_pc, offset	@ Correct PC for prefetching
65		bic	sv_pc, sv_pc, mask	@ mask PC/LR for the mode
66
671003:		ldr	r2, [sv_pc, #-4]	@ if stmfd sp!, {args} exists,
68		ldr	r3, .Ldsi+4		@ adjust saved 'pc' back one
69		teq	r3, r2, lsr #11		@ instruction
70		subne	r0, sv_pc, #4		@ allow for mov
71		subeq	r0, sv_pc, #8		@ allow for mov + stmia
72
73		ldr	r1, [frame, #-4]	@ get saved lr
74		mov	r2, frame
75		bic	r1, r1, mask		@ mask PC/LR for the mode
76		bl	dump_backtrace_entry
77
78		ldr	r1, [sv_pc, #-4]	@ if stmfd sp!, {args} exists,
79		ldr	r3, .Ldsi+4
80		teq	r3, r1, lsr #11
81		ldreq	r0, [frame, #-8]	@ get sp
82		subeq	r0, r0, #4		@ point at the last arg
83		bleq	dump_backtrace_stm	@ dump saved registers
84
851004:		ldr	r1, [sv_pc, #0]		@ if stmfd sp!, {..., fp, ip, lr, pc}
86		ldr	r3, .Ldsi		@ instruction exists,
87		teq	r3, r1, lsr #11
88		subeq	r0, frame, #16
89		bleq	dump_backtrace_stm	@ dump saved registers
90
91		teq	sv_fp, #0		@ zero saved fp means
92		beq	no_frame		@ no further frames
93
94		cmp	sv_fp, frame		@ next frame must be
95		mov	frame, sv_fp		@ above the current frame
96		bhi	for_each_frame
97
981006:		adr	r0, .Lbad
99		mov	r1, frame
100		bl	printk
101no_frame:	ldmfd	sp!, {r4 - r8, pc}
102ENDPROC(c_backtrace)
103
104		.pushsection __ex_table,"a"
105		.align	3
106		.long	1001b, 1006b
107		.long	1002b, 1006b
108		.long	1003b, 1006b
109		.long	1004b, 1006b
110		.popsection
111
112.Lbad:		.asciz	"Backtrace aborted due to bad frame pointer <%p>\n"
113		.align
114.Ldsi:		.word	0xe92dd800 >> 11	@ stmfd sp!, {... fp, ip, lr, pc}
115		.word	0xe92d0000 >> 11	@ stmfd sp!, {}
116
117#endif
118