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Linux/arch/arm/kernel/ftrace.c

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  1 /*
  2  * Dynamic function tracing support.
  3  *
  4  * Copyright (C) 2008 Abhishek Sagar <sagar.abhishek@gmail.com>
  5  * Copyright (C) 2010 Rabin Vincent <rabin@rab.in>
  6  *
  7  * For licencing details, see COPYING.
  8  *
  9  * Defines low-level handling of mcount calls when the kernel
 10  * is compiled with the -pg flag. When using dynamic ftrace, the
 11  * mcount call-sites get patched with NOP till they are enabled.
 12  * All code mutation routines here are called under stop_machine().
 13  */
 14 
 15 #include <linux/ftrace.h>
 16 #include <linux/uaccess.h>
 17 #include <linux/module.h>
 18 #include <linux/stop_machine.h>
 19 
 20 #include <asm/cacheflush.h>
 21 #include <asm/opcodes.h>
 22 #include <asm/ftrace.h>
 23 #include <asm/insn.h>
 24 
 25 #ifdef CONFIG_THUMB2_KERNEL
 26 #define NOP             0xf85deb04      /* pop.w {lr} */
 27 #else
 28 #define NOP             0xe8bd4000      /* pop {lr} */
 29 #endif
 30 
 31 #ifdef CONFIG_DYNAMIC_FTRACE
 32 #ifdef CONFIG_OLD_MCOUNT
 33 #define OLD_MCOUNT_ADDR ((unsigned long) mcount)
 34 #define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
 35 
 36 #define OLD_NOP         0xe1a00000      /* mov r0, r0 */
 37 
 38 static int __ftrace_modify_code(void *data)
 39 {
 40         int *command = data;
 41 
 42         set_kernel_text_rw();
 43         ftrace_modify_all_code(*command);
 44         set_kernel_text_ro();
 45 
 46         return 0;
 47 }
 48 
 49 void arch_ftrace_update_code(int command)
 50 {
 51         stop_machine(__ftrace_modify_code, &command, NULL);
 52 }
 53 
 54 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
 55 {
 56         return rec->arch.old_mcount ? OLD_NOP : NOP;
 57 }
 58 
 59 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
 60 {
 61         if (!rec->arch.old_mcount)
 62                 return addr;
 63 
 64         if (addr == MCOUNT_ADDR)
 65                 addr = OLD_MCOUNT_ADDR;
 66         else if (addr == FTRACE_ADDR)
 67                 addr = OLD_FTRACE_ADDR;
 68 
 69         return addr;
 70 }
 71 #else
 72 static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
 73 {
 74         return NOP;
 75 }
 76 
 77 static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
 78 {
 79         return addr;
 80 }
 81 #endif
 82 
 83 int ftrace_arch_code_modify_prepare(void)
 84 {
 85         set_all_modules_text_rw();
 86         return 0;
 87 }
 88 
 89 int ftrace_arch_code_modify_post_process(void)
 90 {
 91         set_all_modules_text_ro();
 92         /* Make sure any TLB misses during machine stop are cleared. */
 93         flush_tlb_all();
 94         return 0;
 95 }
 96 
 97 static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
 98 {
 99         return arm_gen_branch_link(pc, addr);
100 }
101 
102 static int ftrace_modify_code(unsigned long pc, unsigned long old,
103                               unsigned long new, bool validate)
104 {
105         unsigned long replaced;
106 
107         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
108                 old = __opcode_to_mem_thumb32(old);
109                 new = __opcode_to_mem_thumb32(new);
110         } else {
111                 old = __opcode_to_mem_arm(old);
112                 new = __opcode_to_mem_arm(new);
113         }
114 
115         if (validate) {
116                 if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
117                         return -EFAULT;
118 
119                 if (replaced != old)
120                         return -EINVAL;
121         }
122 
123         if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
124                 return -EPERM;
125 
126         flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
127 
128         return 0;
129 }
130 
131 int ftrace_update_ftrace_func(ftrace_func_t func)
132 {
133         unsigned long pc;
134         unsigned long new;
135         int ret;
136 
137         pc = (unsigned long)&ftrace_call;
138         new = ftrace_call_replace(pc, (unsigned long)func);
139 
140         ret = ftrace_modify_code(pc, 0, new, false);
141 
142 #ifdef CONFIG_OLD_MCOUNT
143         if (!ret) {
144                 pc = (unsigned long)&ftrace_call_old;
145                 new = ftrace_call_replace(pc, (unsigned long)func);
146 
147                 ret = ftrace_modify_code(pc, 0, new, false);
148         }
149 #endif
150 
151         return ret;
152 }
153 
154 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
155 {
156         unsigned long new, old;
157         unsigned long ip = rec->ip;
158 
159         old = ftrace_nop_replace(rec);
160         new = ftrace_call_replace(ip, adjust_address(rec, addr));
161 
162         return ftrace_modify_code(rec->ip, old, new, true);
163 }
164 
165 int ftrace_make_nop(struct module *mod,
166                     struct dyn_ftrace *rec, unsigned long addr)
167 {
168         unsigned long ip = rec->ip;
169         unsigned long old;
170         unsigned long new;
171         int ret;
172 
173         old = ftrace_call_replace(ip, adjust_address(rec, addr));
174         new = ftrace_nop_replace(rec);
175         ret = ftrace_modify_code(ip, old, new, true);
176 
177 #ifdef CONFIG_OLD_MCOUNT
178         if (ret == -EINVAL && addr == MCOUNT_ADDR) {
179                 rec->arch.old_mcount = true;
180 
181                 old = ftrace_call_replace(ip, adjust_address(rec, addr));
182                 new = ftrace_nop_replace(rec);
183                 ret = ftrace_modify_code(ip, old, new, true);
184         }
185 #endif
186 
187         return ret;
188 }
189 
190 int __init ftrace_dyn_arch_init(void)
191 {
192         return 0;
193 }
194 #endif /* CONFIG_DYNAMIC_FTRACE */
195 
196 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
197 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
198                            unsigned long frame_pointer)
199 {
200         unsigned long return_hooker = (unsigned long) &return_to_handler;
201         struct ftrace_graph_ent trace;
202         unsigned long old;
203         int err;
204 
205         if (unlikely(atomic_read(&current->tracing_graph_pause)))
206                 return;
207 
208         old = *parent;
209         *parent = return_hooker;
210 
211         trace.func = self_addr;
212         trace.depth = current->curr_ret_stack + 1;
213 
214         /* Only trace if the calling function expects to */
215         if (!ftrace_graph_entry(&trace)) {
216                 *parent = old;
217                 return;
218         }
219 
220         err = ftrace_push_return_trace(old, self_addr, &trace.depth,
221                                        frame_pointer, NULL);
222         if (err == -EBUSY) {
223                 *parent = old;
224                 return;
225         }
226 }
227 
228 #ifdef CONFIG_DYNAMIC_FTRACE
229 extern unsigned long ftrace_graph_call;
230 extern unsigned long ftrace_graph_call_old;
231 extern void ftrace_graph_caller_old(void);
232 
233 static int __ftrace_modify_caller(unsigned long *callsite,
234                                   void (*func) (void), bool enable)
235 {
236         unsigned long caller_fn = (unsigned long) func;
237         unsigned long pc = (unsigned long) callsite;
238         unsigned long branch = arm_gen_branch(pc, caller_fn);
239         unsigned long nop = 0xe1a00000; /* mov r0, r0 */
240         unsigned long old = enable ? nop : branch;
241         unsigned long new = enable ? branch : nop;
242 
243         return ftrace_modify_code(pc, old, new, true);
244 }
245 
246 static int ftrace_modify_graph_caller(bool enable)
247 {
248         int ret;
249 
250         ret = __ftrace_modify_caller(&ftrace_graph_call,
251                                      ftrace_graph_caller,
252                                      enable);
253 
254 #ifdef CONFIG_OLD_MCOUNT
255         if (!ret)
256                 ret = __ftrace_modify_caller(&ftrace_graph_call_old,
257                                              ftrace_graph_caller_old,
258                                              enable);
259 #endif
260 
261         return ret;
262 }
263 
264 int ftrace_enable_ftrace_graph_caller(void)
265 {
266         return ftrace_modify_graph_caller(true);
267 }
268 
269 int ftrace_disable_ftrace_graph_caller(void)
270 {
271         return ftrace_modify_graph_caller(false);
272 }
273 #endif /* CONFIG_DYNAMIC_FTRACE */
274 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
275 

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