arch/arm/lib/backtrace.S

   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
  23 ENTRY(c_backtrace)
  24
  25 #if !defined(CONFIG_FRAME_POINTER) || !defined(CONFIG_PRINTK)
  26                 ret     lr
  27 ENDPROC(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
  40 1:              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  */
  60 for_each_frame: tst     frame, mask             @ Check for address exceptions
  61                 bne     no_frame
  62
  63 1001:           ldr     sv_pc, [frame, #0]      @ get saved pc
  64 1002:           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
  69 1003:           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
  89 1004:           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
 103 1006:           adr     r0, .Lbad
 104                 mov     r1, loglvl
 105                 mov     r2, frame
 106                 bl      printk
 107 no_frame:       ldmfd   sp!, {r4 - r9, pc}
 108 ENDPROC(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