2 * Dynamic function tracer architecture backend.
4 * Copyright IBM Corp. 2009,2014
6 * Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
7 * Martin Schwidefsky <schwidefsky@de.ibm.com>
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>
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
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
52 * > brcl 0,0 # offset 0
53 * To enable ftrace the code gets patched like above and afterwards looks
55 * > brasl %r0,ftrace_caller # offset 0
58 void *ftrace_func __read_mostly = ftrace_stub;
59 unsigned long ftrace_plt;
61 static inline void ftrace_generate_orig_insn(struct ftrace_insn *insn)
63 #ifdef CC_USING_HOTPATCH
70 insn->disp = 0xf0080024;
74 static inline int is_kprobe_on_ftrace(struct ftrace_insn *insn)
77 if (insn->opc == BREAKPOINT_INSTRUCTION)
83 static inline void ftrace_generate_kprobe_nop_insn(struct ftrace_insn *insn)
86 insn->opc = BREAKPOINT_INSTRUCTION;
87 insn->disp = KPROBE_ON_FTRACE_NOP;
91 static inline void ftrace_generate_kprobe_call_insn(struct ftrace_insn *insn)
94 insn->opc = BREAKPOINT_INSTRUCTION;
95 insn->disp = KPROBE_ON_FTRACE_CALL;
99 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
105 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
108 struct ftrace_insn orig, new, old;
110 if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
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)) {
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.
124 ftrace_generate_kprobe_call_insn(&orig);
125 ftrace_generate_kprobe_nop_insn(&new);
127 /* Replace ftrace call with a nop. */
128 ftrace_generate_call_insn(&orig, rec->ip);
129 ftrace_generate_nop_insn(&new);
131 /* Verify that the to be replaced code matches what we expect. */
132 if (memcmp(&orig, &old, sizeof(old)))
134 s390_kernel_write((void *) rec->ip, &new, sizeof(new));
138 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
140 struct ftrace_insn orig, new, old;
142 if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
144 if (is_kprobe_on_ftrace(&old)) {
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.
152 ftrace_generate_kprobe_nop_insn(&orig);
153 ftrace_generate_kprobe_call_insn(&new);
155 /* Replace nop with an ftrace call. */
156 ftrace_generate_nop_insn(&orig);
157 ftrace_generate_call_insn(&new, rec->ip);
159 /* Verify that the to be replaced code matches what we expect. */
160 if (memcmp(&orig, &old, sizeof(old)))
162 s390_kernel_write((void *) rec->ip, &new, sizeof(new));
166 int ftrace_update_ftrace_func(ftrace_func_t func)
172 int __init ftrace_dyn_arch_init(void)
177 static int __init ftrace_plt_init(void)
181 ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE);
183 panic("cannot allocate ftrace plt\n");
184 ip = (unsigned int *) ftrace_plt;
185 ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */
188 ip[3] = FTRACE_ADDR >> 32;
189 ip[4] = FTRACE_ADDR & 0xffffffff;
190 set_memory_ro(ftrace_plt, 1);
193 device_initcall(ftrace_plt_init);
195 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
197 * Hook the return address and push it in the stack of return addresses
198 * in current thread info.
200 unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip)
202 struct ftrace_graph_ent trace;
204 if (unlikely(ftrace_graph_is_dead()))
206 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
208 ip -= MCOUNT_INSN_SIZE;
210 trace.depth = current->curr_ret_stack + 1;
211 /* Only trace if the calling function expects to. */
212 if (!ftrace_graph_entry(&trace))
214 if (ftrace_push_return_trace(parent, ip, &trace.depth, 0,
217 parent = (unsigned long) return_to_handler;
221 NOKPROBE_SYMBOL(prepare_ftrace_return);
224 * Patch the kernel code at ftrace_graph_caller location. The instruction
225 * there is branch relative on condition. To enable the ftrace graph code
226 * block, we simply patch the mask field of the instruction to zero and
227 * turn the instruction into a nop.
228 * To disable the ftrace graph code the mask field will be patched to
229 * all ones, which turns the instruction into an unconditional branch.
231 int ftrace_enable_ftrace_graph_caller(void)
233 u8 op = 0x04; /* set mask field to zero */
235 s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
239 int ftrace_disable_ftrace_graph_caller(void)
241 u8 op = 0xf4; /* set mask field to all ones */
243 s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
247 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */