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 #include "entry.h" 19 20 #ifdef CONFIG_DYNAMIC_FTRACE 21 22 void ftrace_disable_code(void); 23 void ftrace_enable_insn(void); 24 25 #ifdef CONFIG_64BIT 26 /* 27 * The 64-bit mcount code looks like this: 28 * stg %r14,8(%r15) # offset 0 29 * > larl %r1,<&counter> # offset 6 30 * > brasl %r14,_mcount # offset 12 31 * lg %r14,8(%r15) # offset 18 32 * Total length is 24 bytes. The middle two instructions of the mcount 33 * block get overwritten by ftrace_make_nop / ftrace_make_call. 34 * The 64-bit enabled ftrace code block looks like this: 35 * stg %r14,8(%r15) # offset 0 36 * > lg %r1,__LC_FTRACE_FUNC # offset 6 37 * > lgr %r0,%r0 # offset 12 38 * > basr %r14,%r1 # offset 16 39 * lg %r14,8(%15) # offset 18 40 * The return points of the mcount/ftrace function have the same offset 18. 41 * The 64-bit disable ftrace code block looks like this: 42 * stg %r14,8(%r15) # offset 0 43 * > jg .+18 # offset 6 44 * > lgr %r0,%r0 # offset 12 45 * > basr %r14,%r1 # offset 16 46 * lg %r14,8(%15) # offset 18 47 * The jg instruction branches to offset 24 to skip as many instructions 48 * as possible. 49 */ 50 asm( 51 " .align 4\n" 52 "ftrace_disable_code:\n" 53 " jg 0f\n" 54 " lgr %r0,%r0\n" 55 " basr %r14,%r1\n" 56 "0:\n" 57 " .align 4\n" 58 "ftrace_enable_insn:\n" 59 " lg %r1,"__stringify(__LC_FTRACE_FUNC)"\n"); 60 61 #define FTRACE_INSN_SIZE 6 62 63 #else /* CONFIG_64BIT */ 64 /* 65 * The 31-bit mcount code looks like this: 66 * st %r14,4(%r15) # offset 0 67 * > bras %r1,0f # offset 4 68 * > .long _mcount # offset 8 69 * > .long <&counter> # offset 12 70 * > 0: l %r14,0(%r1) # offset 16 71 * > l %r1,4(%r1) # offset 20 72 * basr %r14,%r14 # offset 24 73 * l %r14,4(%r15) # offset 26 74 * Total length is 30 bytes. The twenty bytes starting from offset 4 75 * to offset 24 get overwritten by ftrace_make_nop / ftrace_make_call. 76 * The 31-bit enabled ftrace code block looks like this: 77 * st %r14,4(%r15) # offset 0 78 * > l %r14,__LC_FTRACE_FUNC # offset 4 79 * > j 0f # offset 8 80 * > .fill 12,1,0x07 # offset 12 81 * 0: basr %r14,%r14 # offset 24 82 * l %r14,4(%r14) # offset 26 83 * The return points of the mcount/ftrace function have the same offset 26. 84 * The 31-bit disabled ftrace code block looks like this: 85 * st %r14,4(%r15) # offset 0 86 * > j .+26 # offset 4 87 * > j 0f # offset 8 88 * > .fill 12,1,0x07 # offset 12 89 * 0: basr %r14,%r14 # offset 24 90 * l %r14,4(%r14) # offset 26 91 * The j instruction branches to offset 30 to skip as many instructions 92 * as possible. 93 */ 94 asm( 95 " .align 4\n" 96 "ftrace_disable_code:\n" 97 " j 1f\n" 98 " j 0f\n" 99 " .fill 12,1,0x07\n" 100 "0: basr %r14,%r14\n" 101 "1:\n" 102 " .align 4\n" 103 "ftrace_enable_insn:\n" 104 " l %r14,"__stringify(__LC_FTRACE_FUNC)"\n"); 105 106 #define FTRACE_INSN_SIZE 4 107 108 #endif /* CONFIG_64BIT */ 109 110 111 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, 112 unsigned long addr) 113 { 114 if (probe_kernel_write((void *) rec->ip, ftrace_disable_code, 115 MCOUNT_INSN_SIZE)) 116 return -EPERM; 117 return 0; 118 } 119 120 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) 121 { 122 if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn, 123 FTRACE_INSN_SIZE)) 124 return -EPERM; 125 return 0; 126 } 127 128 int ftrace_update_ftrace_func(ftrace_func_t func) 129 { 130 return 0; 131 } 132 133 int __init ftrace_dyn_arch_init(void *data) 134 { 135 *(unsigned long *) data = 0; 136 return 0; 137 } 138 139 #endif /* CONFIG_DYNAMIC_FTRACE */ 140 141 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 142 /* 143 * Hook the return address and push it in the stack of return addresses 144 * in current thread info. 145 */ 146 unsigned long __kprobes prepare_ftrace_return(unsigned long parent, 147 unsigned long ip) 148 { 149 struct ftrace_graph_ent trace; 150 151 if (unlikely(atomic_read(¤t->tracing_graph_pause))) 152 goto out; 153 ip = (ip & PSW_ADDR_INSN) - MCOUNT_INSN_SIZE; 154 trace.func = ip; 155 trace.depth = current->curr_ret_stack + 1; 156 /* Only trace if the calling function expects to. */ 157 if (!ftrace_graph_entry(&trace)) 158 goto out; 159 if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY) 160 goto out; 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((void *) 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((void *) ftrace_graph_caller + 2, 189 &offset, sizeof(offset)); 190 } 191 192 #endif /* CONFIG_DYNAMIC_FTRACE */ 193 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 194