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 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, 61 unsigned long addr) 62 { 63 return 0; 64 } 65 66 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, 67 unsigned long addr) 68 { 69 struct ftrace_insn orig, new, old; 70 71 if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old))) 72 return -EFAULT; 73 if (addr == MCOUNT_ADDR) { 74 /* Initial code replacement */ 75 #ifdef CC_USING_HOTPATCH 76 /* We expect to see brcl 0,0 */ 77 ftrace_generate_nop_insn(&orig); 78 #else 79 /* We expect to see stg r14,8(r15) */ 80 orig.opc = 0xe3e0; 81 orig.disp = 0xf0080024; 82 #endif 83 ftrace_generate_nop_insn(&new); 84 } else if (old.opc == BREAKPOINT_INSTRUCTION) { 85 /* 86 * If we find a breakpoint instruction, a kprobe has been 87 * placed at the beginning of the function. We write the 88 * constant KPROBE_ON_FTRACE_NOP into the remaining four 89 * bytes of the original instruction so that the kprobes 90 * handler can execute a nop, if it reaches this breakpoint. 91 */ 92 new.opc = orig.opc = BREAKPOINT_INSTRUCTION; 93 orig.disp = KPROBE_ON_FTRACE_CALL; 94 new.disp = KPROBE_ON_FTRACE_NOP; 95 } else { 96 /* Replace ftrace call with a nop. */ 97 ftrace_generate_call_insn(&orig, rec->ip); 98 ftrace_generate_nop_insn(&new); 99 } 100 /* Verify that the to be replaced code matches what we expect. */ 101 if (memcmp(&orig, &old, sizeof(old))) 102 return -EINVAL; 103 if (probe_kernel_write((void *) rec->ip, &new, sizeof(new))) 104 return -EPERM; 105 return 0; 106 } 107 108 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) 109 { 110 struct ftrace_insn orig, new, old; 111 112 if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old))) 113 return -EFAULT; 114 if (old.opc == BREAKPOINT_INSTRUCTION) { 115 /* 116 * If we find a breakpoint instruction, a kprobe has been 117 * placed at the beginning of the function. We write the 118 * constant KPROBE_ON_FTRACE_CALL into the remaining four 119 * bytes of the original instruction so that the kprobes 120 * handler can execute a brasl if it reaches this breakpoint. 121 */ 122 new.opc = orig.opc = BREAKPOINT_INSTRUCTION; 123 orig.disp = KPROBE_ON_FTRACE_NOP; 124 new.disp = KPROBE_ON_FTRACE_CALL; 125 } else { 126 /* Replace nop with an ftrace call. */ 127 ftrace_generate_nop_insn(&orig); 128 ftrace_generate_call_insn(&new, rec->ip); 129 } 130 /* Verify that the to be replaced code matches what we expect. */ 131 if (memcmp(&orig, &old, sizeof(old))) 132 return -EINVAL; 133 if (probe_kernel_write((void *) rec->ip, &new, sizeof(new))) 134 return -EPERM; 135 return 0; 136 } 137 138 int ftrace_update_ftrace_func(ftrace_func_t func) 139 { 140 return 0; 141 } 142 143 int __init ftrace_dyn_arch_init(void) 144 { 145 return 0; 146 } 147 148 static int __init ftrace_plt_init(void) 149 { 150 unsigned int *ip; 151 152 ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE); 153 if (!ftrace_plt) 154 panic("cannot allocate ftrace plt\n"); 155 ip = (unsigned int *) ftrace_plt; 156 ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */ 157 ip[1] = 0x100a0004; 158 ip[2] = 0x07f10000; 159 ip[3] = FTRACE_ADDR >> 32; 160 ip[4] = FTRACE_ADDR & 0xffffffff; 161 set_memory_ro(ftrace_plt, 1); 162 return 0; 163 } 164 device_initcall(ftrace_plt_init); 165 166 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 167 /* 168 * Hook the return address and push it in the stack of return addresses 169 * in current thread info. 170 */ 171 unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip) 172 { 173 struct ftrace_graph_ent trace; 174 175 if (unlikely(ftrace_graph_is_dead())) 176 goto out; 177 if (unlikely(atomic_read(¤t->tracing_graph_pause))) 178 goto out; 179 ip = (ip & PSW_ADDR_INSN) - MCOUNT_INSN_SIZE; 180 trace.func = ip; 181 trace.depth = current->curr_ret_stack + 1; 182 /* Only trace if the calling function expects to. */ 183 if (!ftrace_graph_entry(&trace)) 184 goto out; 185 if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY) 186 goto out; 187 parent = (unsigned long) return_to_handler; 188 out: 189 return parent; 190 } 191 NOKPROBE_SYMBOL(prepare_ftrace_return); 192 193 /* 194 * Patch the kernel code at ftrace_graph_caller location. The instruction 195 * there is branch relative on condition. To enable the ftrace graph code 196 * block, we simply patch the mask field of the instruction to zero and 197 * turn the instruction into a nop. 198 * To disable the ftrace graph code the mask field will be patched to 199 * all ones, which turns the instruction into an unconditional branch. 200 */ 201 int ftrace_enable_ftrace_graph_caller(void) 202 { 203 u8 op = 0x04; /* set mask field to zero */ 204 205 return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op)); 206 } 207 208 int ftrace_disable_ftrace_graph_caller(void) 209 { 210 u8 op = 0xf4; /* set mask field to all ones */ 211 212 return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op)); 213 } 214 215 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 216