arch/arm/kernel/entry-ftrace.S

   1 /*
   2  * This program is free software; you can redistribute it and/or modify
   3  * it under the terms of the GNU General Public License version 2 as
   4  * published by the Free Software Foundation.
   5  */
   6
   7 #include <asm/assembler.h>
   8 #include <asm/ftrace.h>
   9 #include <asm/unwind.h>
  10
  11 #include "entry-header.S"
  12
  13 /*
  14  * When compiling with -pg, gcc inserts a call to the mcount routine at the
  15  * start of every function.  In mcount, apart from the function's address (in
  16  * lr), we need to get hold of the function's caller's address.
  17  *
  18  * Older GCCs (pre-4.4) inserted a call to a routine called mcount like this:
  19  *
  20  *      bl      mcount
  21  *
  22  * These versions have the limitation that in order for the mcount routine to
  23  * be able to determine the function's caller's address, an APCS-style frame
  24  * pointer (which is set up with something like the code below) is required.
  25  *
  26  *      mov     ip, sp
  27  *      push    {fp, ip, lr, pc}
  28  *      sub     fp, ip, #4
  29  *
  30  * With EABI, these frame pointers are not available unless -mapcs-frame is
  31  * specified, and if building as Thumb-2, not even then.
  32  *
  33  * Newer GCCs (4.4+) solve this problem by introducing a new version of mcount,
  34  * with call sites like:
  35  *
  36  *      push    {lr}
  37  *      bl      __gnu_mcount_nc
  38  *
  39  * With these compilers, frame pointers are not necessary.
  40  *
  41  * mcount can be thought of as a function called in the middle of a subroutine
  42  * call.  As such, it needs to be transparent for both the caller and the
  43  * callee: the original lr needs to be restored when leaving mcount, and no
  44  * registers should be clobbered.  (In the __gnu_mcount_nc implementation, we
  45  * clobber the ip register.  This is OK because the ARM calling convention
  46  * allows it to be clobbered in subroutines and doesn't use it to hold
  47  * parameters.)
  48  *
  49  * When using dynamic ftrace, we patch out the mcount call by a "mov r0, r0"
  50  * for the mcount case, and a "pop {lr}" for the __gnu_mcount_nc case (see
  51  * arch/arm/kernel/ftrace.c).
  52  */
  53
  54 #ifndef CONFIG_OLD_MCOUNT
  55 #if (__GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 4))
  56 #error Ftrace requires CONFIG_FRAME_POINTER=y with GCC older than 4.4.0.
  57 #endif
  58 #endif
  59
  60 .macro mcount_adjust_addr rd, rn
  61         bic     \rd, \rn, #1            @ clear the Thumb bit if present
  62         sub     \rd, \rd, #MCOUNT_INSN_SIZE
  63 .endm
  64
  65 .macro __mcount suffix
  66         mcount_enter
  67         ldr     r0, =ftrace_trace_function
  68         ldr     r2, [r0]
  69         adr     r0, .Lftrace_stub
  70         cmp     r0, r2
  71         bne     1f
  72
  73 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
  74         ldr     r1, =ftrace_graph_return
  75         ldr     r2, [r1]
  76         cmp     r0, r2
  77         bne     ftrace_graph_caller\suffix
  78
  79         ldr     r1, =ftrace_graph_entry
  80         ldr     r2, [r1]
  81         ldr     r0, =ftrace_graph_entry_stub
  82         cmp     r0, r2
  83         bne     ftrace_graph_caller\suffix
  84 #endif
  85
  86         mcount_exit
  87
  88 1:      mcount_get_lr   r1                      @ lr of instrumented func
  89         mcount_adjust_addr      r0, lr          @ instrumented function
  90         badr    lr, 2f
  91         mov     pc, r2
  92 2:      mcount_exit
  93 .endm
  94
  95 .macro __ftrace_caller suffix
  96         mcount_enter
  97
  98         mcount_get_lr   r1                      @ lr of instrumented func
  99         mcount_adjust_addr      r0, lr          @ instrumented function
 100
 101         .globl ftrace_call\suffix
 102 ftrace_call\suffix:
 103         bl      ftrace_stub
 104
 105 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 106         .globl ftrace_graph_call\suffix
 107 ftrace_graph_call\suffix:
 108         mov     r0, r0
 109 #endif
 110
 111         mcount_exit
 112 .endm
 113
 114 .macro __ftrace_graph_caller
 115         sub     r0, fp, #4              @ &lr of instrumented routine (&parent)
 116 #ifdef CONFIG_DYNAMIC_FTRACE
 117         @ called from __ftrace_caller, saved in mcount_enter
 118         ldr     r1, [sp, #16]           @ instrumented routine (func)
 119         mcount_adjust_addr      r1, r1
 120 #else
 121         @ called from __mcount, untouched in lr
 122         mcount_adjust_addr      r1, lr  @ instrumented routine (func)
 123 #endif
 124         mov     r2, fp                  @ frame pointer
 125         bl      prepare_ftrace_return
 126         mcount_exit
 127 .endm
 128
 129 #ifdef CONFIG_OLD_MCOUNT
 130 /*
 131  * mcount
 132  */
 133
 134 .macro mcount_enter
 135         stmdb   sp!, {r0-r3, lr}
 136 .endm
 137
 138 .macro mcount_get_lr reg
 139         ldr     \reg, [fp, #-4]
 140 .endm
 141
 142 .macro mcount_exit
 143         ldr     lr, [fp, #-4]
 144         ldmia   sp!, {r0-r3, pc}
 145 .endm
 146
 147 ENTRY(mcount)
 148 #ifdef CONFIG_DYNAMIC_FTRACE
 149         stmdb   sp!, {lr}
 150         ldr     lr, [fp, #-4]
 151         ldmia   sp!, {pc}
 152 #else
 153         __mcount _old
 154 #endif
 155 ENDPROC(mcount)
 156
 157 #ifdef CONFIG_DYNAMIC_FTRACE
 158 ENTRY(ftrace_caller_old)
 159         __ftrace_caller _old
 160 ENDPROC(ftrace_caller_old)
 161 #endif
 162
 163 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 164 ENTRY(ftrace_graph_caller_old)
 165         __ftrace_graph_caller
 166 ENDPROC(ftrace_graph_caller_old)
 167 #endif
 168
 169 .purgem mcount_enter
 170 .purgem mcount_get_lr
 171 .purgem mcount_exit
 172 #endif
 173
 174 /*
 175  * __gnu_mcount_nc
 176  */
 177
 178 .macro mcount_enter
 179 /*
 180  * This pad compensates for the push {lr} at the call site.  Note that we are
 181  * unable to unwind through a function which does not otherwise save its lr.
 182  */
 183  UNWIND(.pad    #4)
 184         stmdb   sp!, {r0-r3, lr}
 185  UNWIND(.save   {r0-r3, lr})
 186 .endm
 187
 188 .macro mcount_get_lr reg
 189         ldr     \reg, [sp, #20]
 190 .endm
 191
 192 .macro mcount_exit
 193         ldmia   sp!, {r0-r3, ip, lr}
 194         ret     ip
 195 .endm
 196
 197 ENTRY(__gnu_mcount_nc)
 198 UNWIND(.fnstart)
 199 #ifdef CONFIG_DYNAMIC_FTRACE
 200         mov     ip, lr
 201         ldmia   sp!, {lr}
 202         ret     ip
 203 #else
 204         __mcount
 205 #endif
 206 UNWIND(.fnend)
 207 ENDPROC(__gnu_mcount_nc)
 208
 209 #ifdef CONFIG_DYNAMIC_FTRACE
 210 ENTRY(ftrace_caller)
 211 UNWIND(.fnstart)
 212         __ftrace_caller
 213 UNWIND(.fnend)
 214 ENDPROC(ftrace_caller)
 215 #endif
 216
 217 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 218 ENTRY(ftrace_graph_caller)
 219 UNWIND(.fnstart)
 220         __ftrace_graph_caller
 221 UNWIND(.fnend)
 222 ENDPROC(ftrace_graph_caller)
 223 #endif
 224
 225 .purgem mcount_enter
 226 .purgem mcount_get_lr
 227 .purgem mcount_exit
 228
 229 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 230         .globl return_to_handler
 231 return_to_handler:
 232         stmdb   sp!, {r0-r3}
 233         mov     r0, fp                  @ frame pointer
 234         bl      ftrace_return_to_handler
 235         mov     lr, r0                  @ r0 has real ret addr
 236         ldmia   sp!, {r0-r3}
 237         ret     lr
 238 #endif
 239
 240 ENTRY(ftrace_stub)
 241 .Lftrace_stub:
 242         ret     lr
 243 ENDPROC(ftrace_stub)