root/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 
  22 ENTRY(c_backtrace)
  23 
  24 #if !defined(CONFIG_FRAME_POINTER) || !defined(CONFIG_PRINTK)
  25                 ret     lr
  26 ENDPROC(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 
  38 1:              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  */
  58 for_each_frame: tst     frame, mask             @ Check for address exceptions
  59                 bne     no_frame
  60 
  61 1001:           ldr     sv_pc, [frame, #0]      @ get saved pc
  62 1002:           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 
  67 1003:           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 
  85 1004:           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 
  98 1006:           adr     r0, .Lbad
  99                 mov     r1, frame
 100                 bl      printk
 101 no_frame:       ldmfd   sp!, {r4 - r8, pc}
 102 ENDPROC(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