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