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