1 /* 2 * Dynamic function tracer architecture backend. 3 * 4 * Copyright IBM Corp. 2009 5 * 6 * Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>, 7 * Martin Schwidefsky <schwidefsky@de.ibm.com> 8 */ 9 10 #include <linux/hardirq.h> 11 #include <linux/uaccess.h> 12 #include <linux/ftrace.h> 13 #include <linux/kernel.h> 14 #include <linux/types.h> 15 #include <linux/kprobes.h> 16 #include <trace/syscall.h> 17 #include <asm/asm-offsets.h> 18 19 #ifdef CONFIG_DYNAMIC_FTRACE 20 21 void ftrace_disable_code(void); 22 void ftrace_enable_insn(void); 23 24 #ifdef CONFIG_64BIT 25 /* 26 * The 64-bit mcount code looks like this: 27 * stg %r14,8(%r15) # offset 0 28 * > larl %r1,<&counter> # offset 6 29 * > brasl %r14,_mcount # offset 12 30 * lg %r14,8(%r15) # offset 18 31 * Total length is 24 bytes. The middle two instructions of the mcount 32 * block get overwritten by ftrace_make_nop / ftrace_make_call. 33 * The 64-bit enabled ftrace code block looks like this: 34 * stg %r14,8(%r15) # offset 0 35 * > lg %r1,__LC_FTRACE_FUNC # offset 6 36 * > lgr %r0,%r0 # offset 12 37 * > basr %r14,%r1 # offset 16 38 * lg %r14,8(%15) # offset 18 39 * The return points of the mcount/ftrace function have the same offset 18. 40 * The 64-bit disable ftrace code block looks like this: 41 * stg %r14,8(%r15) # offset 0 42 * > jg .+18 # offset 6 43 * > lgr %r0,%r0 # offset 12 44 * > basr %r14,%r1 # offset 16 45 * lg %r14,8(%15) # offset 18 46 * The jg instruction branches to offset 24 to skip as many instructions 47 * as possible. 48 */ 49 asm( 50 " .align 4\n" 51 "ftrace_disable_code:\n" 52 " jg 0f\n" 53 " lgr %r0,%r0\n" 54 " basr %r14,%r1\n" 55 "0:\n" 56 " .align 4\n" 57 "ftrace_enable_insn:\n" 58 " lg %r1,"__stringify(__LC_FTRACE_FUNC)"\n"); 59 60 #define FTRACE_INSN_SIZE 6 61 62 #else /* CONFIG_64BIT */ 63 /* 64 * The 31-bit mcount code looks like this: 65 * st %r14,4(%r15) # offset 0 66 * > bras %r1,0f # offset 4 67 * > .long _mcount # offset 8 68 * > .long <&counter> # offset 12 69 * > 0: l %r14,0(%r1) # offset 16 70 * > l %r1,4(%r1) # offset 20 71 * basr %r14,%r14 # offset 24 72 * l %r14,4(%r15) # offset 26 73 * Total length is 30 bytes. The twenty bytes starting from offset 4 74 * to offset 24 get overwritten by ftrace_make_nop / ftrace_make_call. 75 * The 31-bit enabled ftrace code block looks like this: 76 * st %r14,4(%r15) # offset 0 77 * > l %r14,__LC_FTRACE_FUNC # offset 4 78 * > j 0f # offset 8 79 * > .fill 12,1,0x07 # offset 12 80 * 0: basr %r14,%r14 # offset 24 81 * l %r14,4(%r14) # offset 26 82 * The return points of the mcount/ftrace function have the same offset 26. 83 * The 31-bit disabled ftrace code block looks like this: 84 * st %r14,4(%r15) # offset 0 85 * > j .+26 # offset 4 86 * > j 0f # offset 8 87 * > .fill 12,1,0x07 # offset 12 88 * 0: basr %r14,%r14 # offset 24 89 * l %r14,4(%r14) # offset 26 90 * The j instruction branches to offset 30 to skip as many instructions 91 * as possible. 92 */ 93 asm( 94 " .align 4\n" 95 "ftrace_disable_code:\n" 96 " j 1f\n" 97 " j 0f\n" 98 " .fill 12,1,0x07\n" 99 "0: basr %r14,%r14\n" 100 "1:\n" 101 " .align 4\n" 102 "ftrace_enable_insn:\n" 103 " l %r14,"__stringify(__LC_FTRACE_FUNC)"\n"); 104 105 #define FTRACE_INSN_SIZE 4 106 107 #endif /* CONFIG_64BIT */ 108 109 110 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, 111 unsigned long addr) 112 { 113 if (probe_kernel_write((void *) rec->ip, ftrace_disable_code, 114 MCOUNT_INSN_SIZE)) 115 return -EPERM; 116 return 0; 117 } 118 119 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) 120 { 121 if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn, 122 FTRACE_INSN_SIZE)) 123 return -EPERM; 124 return 0; 125 } 126 127 int ftrace_update_ftrace_func(ftrace_func_t func) 128 { 129 return 0; 130 } 131 132 int __init ftrace_dyn_arch_init(void *data) 133 { 134 *(unsigned long *) data = 0; 135 return 0; 136 } 137 138 #endif /* CONFIG_DYNAMIC_FTRACE */ 139 140 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 141 /* 142 * Hook the return address and push it in the stack of return addresses 143 * in current thread info. 144 */ 145 unsigned long __kprobes prepare_ftrace_return(unsigned long parent, 146 unsigned long ip) 147 { 148 struct ftrace_graph_ent trace; 149 150 if (unlikely(atomic_read(¤t->tracing_graph_pause))) 151 goto out; 152 ip = (ip & PSW_ADDR_INSN) - MCOUNT_INSN_SIZE; 153 if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY) 154 goto out; 155 trace.func = ip; 156 /* Only trace if the calling function expects to. */ 157 if (!ftrace_graph_entry(&trace)) { 158 current->curr_ret_stack--; 159 goto out; 160 } 161 parent = (unsigned long) return_to_handler; 162 out: 163 return parent; 164 } 165 166 #ifdef CONFIG_DYNAMIC_FTRACE 167 /* 168 * Patch the kernel code at ftrace_graph_caller location. The instruction 169 * there is branch relative and save to prepare_ftrace_return. To disable 170 * the call to prepare_ftrace_return we patch the bras offset to point 171 * directly after the instructions. To enable the call we calculate 172 * the original offset to prepare_ftrace_return and put it back. 173 */ 174 int ftrace_enable_ftrace_graph_caller(void) 175 { 176 unsigned short offset; 177 178 offset = ((void *) prepare_ftrace_return - 179 (void *) ftrace_graph_caller) / 2; 180 return probe_kernel_write(ftrace_graph_caller + 2, 181 &offset, sizeof(offset)); 182 } 183 184 int ftrace_disable_ftrace_graph_caller(void) 185 { 186 static unsigned short offset = 0x0002; 187 188 return probe_kernel_write(ftrace_graph_caller + 2, 189 &offset, sizeof(offset)); 190 } 191 192 #endif /* CONFIG_DYNAMIC_FTRACE */ 193 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 194