1 /* 2 * Dynamic function tracer architecture backend. 3 * 4 * Copyright IBM Corp. 2009,2014 5 * 6 * Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>, 7 * Martin Schwidefsky <schwidefsky@de.ibm.com> 8 */ 9 10 #include <linux/moduleloader.h> 11 #include <linux/hardirq.h> 12 #include <linux/uaccess.h> 13 #include <linux/ftrace.h> 14 #include <linux/kernel.h> 15 #include <linux/types.h> 16 #include <linux/kprobes.h> 17 #include <trace/syscall.h> 18 #include <asm/asm-offsets.h> 19 #include <asm/cacheflush.h> 20 #include <asm/set_memory.h> 21 #include "entry.h" 22 23 /* 24 * The mcount code looks like this: 25 * stg %r14,8(%r15) # offset 0 26 * larl %r1,<&counter> # offset 6 27 * brasl %r14,_mcount # offset 12 28 * lg %r14,8(%r15) # offset 18 29 * Total length is 24 bytes. Only the first instruction will be patched 30 * by ftrace_make_call / ftrace_make_nop. 31 * The enabled ftrace code block looks like this: 32 * > brasl %r0,ftrace_caller # offset 0 33 * larl %r1,<&counter> # offset 6 34 * brasl %r14,_mcount # offset 12 35 * lg %r14,8(%r15) # offset 18 36 * The ftrace function gets called with a non-standard C function call ABI 37 * where r0 contains the return address. It is also expected that the called 38 * function only clobbers r0 and r1, but restores r2-r15. 39 * For module code we can't directly jump to ftrace caller, but need a 40 * trampoline (ftrace_plt), which clobbers also r1. 41 * The return point of the ftrace function has offset 24, so execution 42 * continues behind the mcount block. 43 * The disabled ftrace code block looks like this: 44 * > jg .+24 # offset 0 45 * larl %r1,<&counter> # offset 6 46 * brasl %r14,_mcount # offset 12 47 * lg %r14,8(%r15) # offset 18 48 * The jg instruction branches to offset 24 to skip as many instructions 49 * as possible. 50 * In case we use gcc's hotpatch feature the original and also the disabled 51 * function prologue contains only a single six byte instruction and looks 52 * like this: 53 * > brcl 0,0 # offset 0 54 * To enable ftrace the code gets patched like above and afterwards looks 55 * like this: 56 * > brasl %r0,ftrace_caller # offset 0 57 */ 58 59 unsigned long ftrace_plt; 60 61 static inline void ftrace_generate_orig_insn(struct ftrace_insn *insn) 62 { 63 #ifdef CC_USING_HOTPATCH 64 /* brcl 0,0 */ 65 insn->opc = 0xc004; 66 insn->disp = 0; 67 #else 68 /* stg r14,8(r15) */ 69 insn->opc = 0xe3e0; 70 insn->disp = 0xf0080024; 71 #endif 72 } 73 74 static inline int is_kprobe_on_ftrace(struct ftrace_insn *insn) 75 { 76 #ifdef CONFIG_KPROBES 77 if (insn->opc == BREAKPOINT_INSTRUCTION) 78 return 1; 79 #endif 80 return 0; 81 } 82 83 static inline void ftrace_generate_kprobe_nop_insn(struct ftrace_insn *insn) 84 { 85 #ifdef CONFIG_KPROBES 86 insn->opc = BREAKPOINT_INSTRUCTION; 87 insn->disp = KPROBE_ON_FTRACE_NOP; 88 #endif 89 } 90 91 static inline void ftrace_generate_kprobe_call_insn(struct ftrace_insn *insn) 92 { 93 #ifdef CONFIG_KPROBES 94 insn->opc = BREAKPOINT_INSTRUCTION; 95 insn->disp = KPROBE_ON_FTRACE_CALL; 96 #endif 97 } 98 99 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, 100 unsigned long addr) 101 { 102 return 0; 103 } 104 105 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, 106 unsigned long addr) 107 { 108 struct ftrace_insn orig, new, old; 109 110 if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old))) 111 return -EFAULT; 112 if (addr == MCOUNT_ADDR) { 113 /* Initial code replacement */ 114 ftrace_generate_orig_insn(&orig); 115 ftrace_generate_nop_insn(&new); 116 } else if (is_kprobe_on_ftrace(&old)) { 117 /* 118 * If we find a breakpoint instruction, a kprobe has been 119 * placed at the beginning of the function. We write the 120 * constant KPROBE_ON_FTRACE_NOP into the remaining four 121 * bytes of the original instruction so that the kprobes 122 * handler can execute a nop, if it reaches this breakpoint. 123 */ 124 ftrace_generate_kprobe_call_insn(&orig); 125 ftrace_generate_kprobe_nop_insn(&new); 126 } else { 127 /* Replace ftrace call with a nop. */ 128 ftrace_generate_call_insn(&orig, rec->ip); 129 ftrace_generate_nop_insn(&new); 130 } 131 /* Verify that the to be replaced code matches what we expect. */ 132 if (memcmp(&orig, &old, sizeof(old))) 133 return -EINVAL; 134 s390_kernel_write((void *) rec->ip, &new, sizeof(new)); 135 return 0; 136 } 137 138 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) 139 { 140 struct ftrace_insn orig, new, old; 141 142 if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old))) 143 return -EFAULT; 144 if (is_kprobe_on_ftrace(&old)) { 145 /* 146 * If we find a breakpoint instruction, a kprobe has been 147 * placed at the beginning of the function. We write the 148 * constant KPROBE_ON_FTRACE_CALL into the remaining four 149 * bytes of the original instruction so that the kprobes 150 * handler can execute a brasl if it reaches this breakpoint. 151 */ 152 ftrace_generate_kprobe_nop_insn(&orig); 153 ftrace_generate_kprobe_call_insn(&new); 154 } else { 155 /* Replace nop with an ftrace call. */ 156 ftrace_generate_nop_insn(&orig); 157 ftrace_generate_call_insn(&new, rec->ip); 158 } 159 /* Verify that the to be replaced code matches what we expect. */ 160 if (memcmp(&orig, &old, sizeof(old))) 161 return -EINVAL; 162 s390_kernel_write((void *) rec->ip, &new, sizeof(new)); 163 return 0; 164 } 165 166 int ftrace_update_ftrace_func(ftrace_func_t func) 167 { 168 return 0; 169 } 170 171 int __init ftrace_dyn_arch_init(void) 172 { 173 return 0; 174 } 175 176 #ifdef CONFIG_MODULES 177 178 static int __init ftrace_plt_init(void) 179 { 180 unsigned int *ip; 181 182 ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE); 183 if (!ftrace_plt) 184 panic("cannot allocate ftrace plt\n"); 185 ip = (unsigned int *) ftrace_plt; 186 ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */ 187 ip[1] = 0x100a0004; 188 ip[2] = 0x07f10000; 189 ip[3] = FTRACE_ADDR >> 32; 190 ip[4] = FTRACE_ADDR & 0xffffffff; 191 set_memory_ro(ftrace_plt, 1); 192 return 0; 193 } 194 device_initcall(ftrace_plt_init); 195 196 #endif /* CONFIG_MODULES */ 197 198 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 199 /* 200 * Hook the return address and push it in the stack of return addresses 201 * in current thread info. 202 */ 203 unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip) 204 { 205 struct ftrace_graph_ent trace; 206 207 if (unlikely(ftrace_graph_is_dead())) 208 goto out; 209 if (unlikely(atomic_read(¤t->tracing_graph_pause))) 210 goto out; 211 ip -= MCOUNT_INSN_SIZE; 212 trace.func = ip; 213 trace.depth = current->curr_ret_stack + 1; 214 /* Only trace if the calling function expects to. */ 215 if (!ftrace_graph_entry(&trace)) 216 goto out; 217 if (ftrace_push_return_trace(parent, ip, &trace.depth, 0, 218 NULL) == -EBUSY) 219 goto out; 220 parent = (unsigned long) return_to_handler; 221 out: 222 return parent; 223 } 224 NOKPROBE_SYMBOL(prepare_ftrace_return); 225 226 /* 227 * Patch the kernel code at ftrace_graph_caller location. The instruction 228 * there is branch relative on condition. To enable the ftrace graph code 229 * block, we simply patch the mask field of the instruction to zero and 230 * turn the instruction into a nop. 231 * To disable the ftrace graph code the mask field will be patched to 232 * all ones, which turns the instruction into an unconditional branch. 233 */ 234 int ftrace_enable_ftrace_graph_caller(void) 235 { 236 u8 op = 0x04; /* set mask field to zero */ 237 238 s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op)); 239 return 0; 240 } 241 242 int ftrace_disable_ftrace_graph_caller(void) 243 { 244 u8 op = 0xf4; /* set mask field to all ones */ 245 246 s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op)); 247 return 0; 248 } 249 250 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 251