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git.proxmox.com Git - mirror_ubuntu-bionic-kernel.git/blob - arch/s390/kernel/ftrace.c
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>
20 #include <asm/set_memory.h>
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
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
53 * > brcl 0,0 # offset 0
54 * To enable ftrace the code gets patched like above and afterwards looks
56 * > brasl %r0,ftrace_caller # offset 0
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
)
171 int __init
ftrace_dyn_arch_init(void)
176 #ifdef CONFIG_MODULES
178 static int __init
ftrace_plt_init(void)
182 ftrace_plt
= (unsigned long) module_alloc(PAGE_SIZE
);
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 */
189 ip
[3] = FTRACE_ADDR
>> 32;
190 ip
[4] = FTRACE_ADDR
& 0xffffffff;
191 set_memory_ro(ftrace_plt
, 1);
194 device_initcall(ftrace_plt_init
);
196 #endif /* CONFIG_MODULES */
198 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
200 * Hook the return address and push it in the stack of return addresses
201 * in current thread info.
203 unsigned long prepare_ftrace_return(unsigned long parent
, unsigned long ip
)
205 struct ftrace_graph_ent trace
;
207 if (unlikely(ftrace_graph_is_dead()))
209 if (unlikely(atomic_read(¤t
->tracing_graph_pause
)))
211 ip
-= MCOUNT_INSN_SIZE
;
213 trace
.depth
= current
->curr_ret_stack
+ 1;
214 /* Only trace if the calling function expects to. */
215 if (!ftrace_graph_entry(&trace
))
217 if (ftrace_push_return_trace(parent
, ip
, &trace
.depth
, 0,
220 parent
= (unsigned long) return_to_handler
;
224 NOKPROBE_SYMBOL(prepare_ftrace_return
);
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.
234 int ftrace_enable_ftrace_graph_caller(void)
236 u8 op
= 0x04; /* set mask field to zero */
238 s390_kernel_write(__va(ftrace_graph_caller
)+1, &op
, sizeof(op
));
242 int ftrace_disable_ftrace_graph_caller(void)
244 u8 op
= 0xf4; /* set mask field to all ones */
246 s390_kernel_write(__va(ftrace_graph_caller
)+1, &op
, sizeof(op
));
250 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */