arch/mips/kernel/ftrace.c

   1 /*
   2  * Code for replacing ftrace calls with jumps.
   3  *
   4  * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
   5  * Copyright (C) 2009, 2010 DSLab, Lanzhou University, China
   6  * Author: Wu Zhangjin <wuzhangjin@gmail.com>
   7  *
   8  * Thanks goes to Steven Rostedt for writing the original x86 version.
   9  */
  10
  11 #include <linux/uaccess.h>
  12 #include <linux/init.h>
  13 #include <linux/ftrace.h>
  14
  15 #include <asm/asm.h>
  16 #include <asm/asm-offsets.h>
  17 #include <asm/cacheflush.h>
  18 #include <asm/uasm.h>
  19
  20 #include <asm-generic/sections.h>
  21
  22 #ifdef CONFIG_DYNAMIC_FTRACE
  23
  24 #define JAL 0x0c000000          /* jump & link: ip --> ra, jump to target */
  25 #define ADDR_MASK 0x03ffffff    /*  op_code|addr : 31...26|25 ....0 */
  26 #define JUMP_RANGE_MASK ((1UL << 28) - 1)
  27
  28 #define INSN_NOP 0x00000000     /* nop */
  29 #define INSN_JAL(addr)  \
  30         ((unsigned int)(JAL | (((addr) >> 2) & ADDR_MASK)))
  31
  32 static unsigned int insn_jal_ftrace_caller __read_mostly;
  33 static unsigned int insn_lui_v1_hi16_mcount __read_mostly;
  34 static unsigned int insn_j_ftrace_graph_caller __maybe_unused __read_mostly;
  35
  36 static inline void ftrace_dyn_arch_init_insns(void)
  37 {
  38         u32 *buf;
  39         unsigned int v1;
  40
  41         /* lui v1, hi16_mcount */
  42         v1 = 3;
  43         buf = (u32 *)&insn_lui_v1_hi16_mcount;
  44         UASM_i_LA_mostly(&buf, v1, MCOUNT_ADDR);
  45
  46         /* jal (ftrace_caller + 8), jump over the first two instruction */
  47         buf = (u32 *)&insn_jal_ftrace_caller;
  48         uasm_i_jal(&buf, (FTRACE_ADDR + 8) & JUMP_RANGE_MASK);
  49
  50 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
  51         /* j ftrace_graph_caller */
  52         buf = (u32 *)&insn_j_ftrace_graph_caller;
  53         uasm_i_j(&buf, (unsigned long)ftrace_graph_caller & JUMP_RANGE_MASK);
  54 #endif
  55 }
  56
  57 /*
  58  * Check if the address is in kernel space
  59  *
  60  * Clone core_kernel_text() from kernel/extable.c, but doesn't call
  61  * init_kernel_text() for Ftrace doesn't trace functions in init sections.
  62  */
  63 static inline int in_kernel_space(unsigned long ip)
  64 {
  65         if (ip >= (unsigned long)_stext &&
  66             ip <= (unsigned long)_etext)
  67                 return 1;
  68         return 0;
  69 }
  70
  71 static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
  72 {
  73         int faulted;
  74
  75         /* *(unsigned int *)ip = new_code; */
  76         safe_store_code(new_code, ip, faulted);
  77
  78         if (unlikely(faulted))
  79                 return -EFAULT;
  80
  81         flush_icache_range(ip, ip + 8);
  82
  83         return 0;
  84 }
  85
  86 /*
  87  * The details about the calling site of mcount on MIPS
  88  *
  89  * 1. For kernel:
  90  *
  91  * move at, ra
  92  * jal _mcount          --> nop
  93  *
  94  * 2. For modules:
  95  *
  96  * 2.1 For KBUILD_MCOUNT_RA_ADDRESS and CONFIG_32BIT
  97  *
  98  * lui v1, hi_16bit_of_mcount        --> b 1f (0x10000005)
  99  * addiu v1, v1, low_16bit_of_mcount
 100  * move at, ra
 101  * move $12, ra_address
 102  * jalr v1
 103  *  sub sp, sp, 8
 104  *                                  1: offset = 5 instructions
 105  * 2.2 For the Other situations
 106  *
 107  * lui v1, hi_16bit_of_mcount        --> b 1f (0x10000004)
 108  * addiu v1, v1, low_16bit_of_mcount
 109  * move at, ra
 110  * jalr v1
 111  *  nop | move $12, ra_address | sub sp, sp, 8
 112  *                                  1: offset = 4 instructions
 113  */
 114
 115 #if defined(KBUILD_MCOUNT_RA_ADDRESS) && defined(CONFIG_32BIT)
 116 #define MCOUNT_OFFSET_INSNS 5
 117 #else
 118 #define MCOUNT_OFFSET_INSNS 4
 119 #endif
 120 #define INSN_B_1F (0x10000000 | MCOUNT_OFFSET_INSNS)
 121
 122 int ftrace_make_nop(struct module *mod,
 123                     struct dyn_ftrace *rec, unsigned long addr)
 124 {
 125         unsigned int new;
 126         unsigned long ip = rec->ip;
 127
 128         /*
 129          * If ip is in kernel space, no long call, otherwise, long call is
 130          * needed.
 131          */
 132         new = in_kernel_space(ip) ? INSN_NOP : INSN_B_1F;
 133
 134         return ftrace_modify_code(ip, new);
 135 }
 136
 137 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 138 {
 139         unsigned int new;
 140         unsigned long ip = rec->ip;
 141
 142         new = in_kernel_space(ip) ? insn_jal_ftrace_caller :
 143                 insn_lui_v1_hi16_mcount;
 144
 145         return ftrace_modify_code(ip, new);
 146 }
 147
 148 #define FTRACE_CALL_IP ((unsigned long)(&ftrace_call))
 149
 150 int ftrace_update_ftrace_func(ftrace_func_t func)
 151 {
 152         unsigned int new;
 153
 154         new = INSN_JAL((unsigned long)func);
 155
 156         return ftrace_modify_code(FTRACE_CALL_IP, new);
 157 }
 158
 159 int __init ftrace_dyn_arch_init(void *data)
 160 {
 161         /* Encode the instructions when booting */
 162         ftrace_dyn_arch_init_insns();
 163
 164         /* Remove "b ftrace_stub" to ensure ftrace_caller() is executed */
 165         ftrace_modify_code(MCOUNT_ADDR, INSN_NOP);
 166
 167         /* The return code is retured via data */
 168         *(unsigned long *)data = 0;
 169
 170         return 0;
 171 }
 172 #endif  /* CONFIG_DYNAMIC_FTRACE */
 173
 174 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 175
 176 #ifdef CONFIG_DYNAMIC_FTRACE
 177
 178 extern void ftrace_graph_call(void);
 179 #define FTRACE_GRAPH_CALL_IP    ((unsigned long)(&ftrace_graph_call))
 180
 181 int ftrace_enable_ftrace_graph_caller(void)
 182 {
 183         return ftrace_modify_code(FTRACE_GRAPH_CALL_IP,
 184                         insn_j_ftrace_graph_caller);
 185 }
 186
 187 int ftrace_disable_ftrace_graph_caller(void)
 188 {
 189         return ftrace_modify_code(FTRACE_GRAPH_CALL_IP, INSN_NOP);
 190 }
 191
 192 #endif  /* CONFIG_DYNAMIC_FTRACE */
 193
 194 #ifndef KBUILD_MCOUNT_RA_ADDRESS
 195
 196 #define S_RA_SP (0xafbf << 16)  /* s{d,w} ra, offset(sp) */
 197 #define S_R_SP  (0xafb0 << 16)  /* s{d,w} R, offset(sp) */
 198 #define OFFSET_MASK     0xffff  /* stack offset range: 0 ~ PT_SIZE */
 199
 200 unsigned long ftrace_get_parent_ra_addr(unsigned long self_ra, unsigned long
 201                 old_parent_ra, unsigned long parent_ra_addr, unsigned long fp)
 202 {
 203         unsigned long sp, ip, tmp;
 204         unsigned int code;
 205         int faulted;
 206
 207         /*
 208          * For module, move the ip from the return address after the
 209          * instruction "lui v1, hi_16bit_of_mcount"(offset is 24), but for
 210          * kernel, move after the instruction "move ra, at"(offset is 16)
 211          */
 212         ip = self_ra - (in_kernel_space(self_ra) ? 16 : 24);
 213
 214         /*
 215          * search the text until finding the non-store instruction or "s{d,w}
 216          * ra, offset(sp)" instruction
 217          */
 218         do {
 219                 /* get the code at "ip": code = *(unsigned int *)ip; */
 220                 safe_load_code(code, ip, faulted);
 221
 222                 if (unlikely(faulted))
 223                         return 0;
 224                 /*
 225                  * If we hit the non-store instruction before finding where the
 226                  * ra is stored, then this is a leaf function and it does not
 227                  * store the ra on the stack
 228                  */
 229                 if ((code & S_R_SP) != S_R_SP)
 230                         return parent_ra_addr;
 231
 232                 /* Move to the next instruction */
 233                 ip -= 4;
 234         } while ((code & S_RA_SP) != S_RA_SP);
 235
 236         sp = fp + (code & OFFSET_MASK);
 237
 238         /* tmp = *(unsigned long *)sp; */
 239         safe_load_stack(tmp, sp, faulted);
 240         if (unlikely(faulted))
 241                 return 0;
 242
 243         if (tmp == old_parent_ra)
 244                 return sp;
 245         return 0;
 246 }
 247
 248 #endif  /* !KBUILD_MCOUNT_RA_ADDRESS */
 249
 250 /*
 251  * Hook the return address and push it in the stack of return addrs
 252  * in current thread info.
 253  */
 254 void prepare_ftrace_return(unsigned long *parent_ra_addr, unsigned long self_ra,
 255                            unsigned long fp)
 256 {
 257         unsigned long old_parent_ra;
 258         struct ftrace_graph_ent trace;
 259         unsigned long return_hooker = (unsigned long)
 260             &return_to_handler;
 261         int faulted, insns;
 262
 263         if (unlikely(atomic_read(&current->tracing_graph_pause)))
 264                 return;
 265
 266         /*
 267          * "parent_ra_addr" is the stack address saved the return address of
 268          * the caller of _mcount.
 269          *
 270          * if the gcc < 4.5, a leaf function does not save the return address
 271          * in the stack address, so, we "emulate" one in _mcount's stack space,
 272          * and hijack it directly, but for a non-leaf function, it save the
 273          * return address to the its own stack space, we can not hijack it
 274          * directly, but need to find the real stack address,
 275          * ftrace_get_parent_addr() does it!
 276          *
 277          * if gcc>= 4.5, with the new -mmcount-ra-address option, for a
 278          * non-leaf function, the location of the return address will be saved
 279          * to $12 for us, and for a leaf function, only put a zero into $12. we
 280          * do it in ftrace_graph_caller of mcount.S.
 281          */
 282
 283         /* old_parent_ra = *parent_ra_addr; */
 284         safe_load_stack(old_parent_ra, parent_ra_addr, faulted);
 285         if (unlikely(faulted))
 286                 goto out;
 287 #ifndef KBUILD_MCOUNT_RA_ADDRESS
 288         parent_ra_addr = (unsigned long *)ftrace_get_parent_ra_addr(self_ra,
 289                         old_parent_ra, (unsigned long)parent_ra_addr, fp);
 290         /*
 291          * If fails when getting the stack address of the non-leaf function's
 292          * ra, stop function graph tracer and return
 293          */
 294         if (parent_ra_addr == 0)
 295                 goto out;
 296 #endif
 297         /* *parent_ra_addr = return_hooker; */
 298         safe_store_stack(return_hooker, parent_ra_addr, faulted);
 299         if (unlikely(faulted))
 300                 goto out;
 301
 302         if (ftrace_push_return_trace(old_parent_ra, self_ra, &trace.depth, fp)
 303             == -EBUSY) {
 304                 *parent_ra_addr = old_parent_ra;
 305                 return;
 306         }
 307
 308         /*
 309          * Get the recorded ip of the current mcount calling site in the
 310          * __mcount_loc section, which will be used to filter the function
 311          * entries configured through the tracing/set_graph_function interface.
 312          */
 313
 314         insns = in_kernel_space(self_ra) ? 2 : MCOUNT_OFFSET_INSNS + 1;
 315         trace.func = self_ra - (MCOUNT_INSN_SIZE * insns);
 316
 317         /* Only trace if the calling function expects to */
 318         if (!ftrace_graph_entry(&trace)) {
 319                 current->curr_ret_stack--;
 320                 *parent_ra_addr = old_parent_ra;
 321         }
 322         return;
 323 out:
 324         ftrace_graph_stop();
 325         WARN_ON(1);
 326 }
 327 #endif  /* CONFIG_FUNCTION_GRAPH_TRACER */