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1 // SPDX-License-Identifier: GPL-2.0
3 * Dynamic function tracer architecture backend.
5 * Copyright IBM Corp. 2009,2014
7 * Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
8 * Martin Schwidefsky <schwidefsky@de.ibm.com>
11 #include <linux/moduleloader.h>
12 #include <linux/hardirq.h>
13 #include <linux/uaccess.h>
14 #include <linux/ftrace.h>
15 #include <linux/kernel.h>
16 #include <linux/types.h>
17 #include <linux/kprobes.h>
18 #include <trace/syscall.h>
19 #include <asm/asm-offsets.h>
20 #include <asm/cacheflush.h>
21 #include <asm/set_memory.h>
25 * The mcount code looks like this:
26 * stg %r14,8(%r15) # offset 0
27 * larl %r1,<&counter> # offset 6
28 * brasl %r14,_mcount # offset 12
29 * lg %r14,8(%r15) # offset 18
30 * Total length is 24 bytes. Only the first instruction will be patched
31 * by ftrace_make_call / ftrace_make_nop.
32 * The enabled ftrace code block looks like this:
33 * > brasl %r0,ftrace_caller # offset 0
34 * larl %r1,<&counter> # offset 6
35 * brasl %r14,_mcount # offset 12
36 * lg %r14,8(%r15) # offset 18
37 * The ftrace function gets called with a non-standard C function call ABI
38 * where r0 contains the return address. It is also expected that the called
39 * function only clobbers r0 and r1, but restores r2-r15.
40 * For module code we can't directly jump to ftrace caller, but need a
41 * trampoline (ftrace_plt), which clobbers also r1.
42 * The return point of the ftrace function has offset 24, so execution
43 * continues behind the mcount block.
44 * The disabled ftrace code block looks like this:
45 * > jg .+24 # offset 0
46 * larl %r1,<&counter> # offset 6
47 * brasl %r14,_mcount # offset 12
48 * lg %r14,8(%r15) # offset 18
49 * The jg instruction branches to offset 24 to skip as many instructions
51 * In case we use gcc's hotpatch feature the original and also the disabled
52 * function prologue contains only a single six byte instruction and looks
54 * > brcl 0,0 # offset 0
55 * To enable ftrace the code gets patched like above and afterwards looks
57 * > brasl %r0,ftrace_caller # offset 0
60 unsigned long ftrace_plt
;
62 static inline void ftrace_generate_orig_insn(struct ftrace_insn
*insn
)
64 #if defined(CC_USING_HOTPATCH) || defined(CC_USING_NOP_MCOUNT)
71 insn
->disp
= 0xf0080024;
75 static inline int is_kprobe_on_ftrace(struct ftrace_insn
*insn
)
78 if (insn
->opc
== BREAKPOINT_INSTRUCTION
)
84 static inline void ftrace_generate_kprobe_nop_insn(struct ftrace_insn
*insn
)
87 insn
->opc
= BREAKPOINT_INSTRUCTION
;
88 insn
->disp
= KPROBE_ON_FTRACE_NOP
;
92 static inline void ftrace_generate_kprobe_call_insn(struct ftrace_insn
*insn
)
95 insn
->opc
= BREAKPOINT_INSTRUCTION
;
96 insn
->disp
= KPROBE_ON_FTRACE_CALL
;
100 int ftrace_modify_call(struct dyn_ftrace
*rec
, unsigned long old_addr
,
106 int ftrace_make_nop(struct module
*mod
, struct dyn_ftrace
*rec
,
109 struct ftrace_insn orig
, new, old
;
111 if (probe_kernel_read(&old
, (void *) rec
->ip
, sizeof(old
)))
113 if (addr
== MCOUNT_ADDR
) {
114 /* Initial code replacement */
115 ftrace_generate_orig_insn(&orig
);
116 ftrace_generate_nop_insn(&new);
117 } else if (is_kprobe_on_ftrace(&old
)) {
119 * If we find a breakpoint instruction, a kprobe has been
120 * placed at the beginning of the function. We write the
121 * constant KPROBE_ON_FTRACE_NOP into the remaining four
122 * bytes of the original instruction so that the kprobes
123 * handler can execute a nop, if it reaches this breakpoint.
125 ftrace_generate_kprobe_call_insn(&orig
);
126 ftrace_generate_kprobe_nop_insn(&new);
128 /* Replace ftrace call with a nop. */
129 ftrace_generate_call_insn(&orig
, rec
->ip
);
130 ftrace_generate_nop_insn(&new);
132 /* Verify that the to be replaced code matches what we expect. */
133 if (memcmp(&orig
, &old
, sizeof(old
)))
135 s390_kernel_write((void *) rec
->ip
, &new, sizeof(new));
139 int ftrace_make_call(struct dyn_ftrace
*rec
, unsigned long addr
)
141 struct ftrace_insn orig
, new, old
;
143 if (probe_kernel_read(&old
, (void *) rec
->ip
, sizeof(old
)))
145 if (is_kprobe_on_ftrace(&old
)) {
147 * If we find a breakpoint instruction, a kprobe has been
148 * placed at the beginning of the function. We write the
149 * constant KPROBE_ON_FTRACE_CALL into the remaining four
150 * bytes of the original instruction so that the kprobes
151 * handler can execute a brasl if it reaches this breakpoint.
153 ftrace_generate_kprobe_nop_insn(&orig
);
154 ftrace_generate_kprobe_call_insn(&new);
156 /* Replace nop with an ftrace call. */
157 ftrace_generate_nop_insn(&orig
);
158 ftrace_generate_call_insn(&new, rec
->ip
);
160 /* Verify that the to be replaced code matches what we expect. */
161 if (memcmp(&orig
, &old
, sizeof(old
)))
163 s390_kernel_write((void *) rec
->ip
, &new, sizeof(new));
167 int ftrace_update_ftrace_func(ftrace_func_t func
)
172 int __init
ftrace_dyn_arch_init(void)
177 #ifdef CONFIG_MODULES
179 static int __init
ftrace_plt_init(void)
183 ftrace_plt
= (unsigned long) module_alloc(PAGE_SIZE
);
185 panic("cannot allocate ftrace plt\n");
186 ip
= (unsigned int *) ftrace_plt
;
187 ip
[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */
190 ip
[3] = FTRACE_ADDR
>> 32;
191 ip
[4] = FTRACE_ADDR
& 0xffffffff;
192 set_memory_ro(ftrace_plt
, 1);
195 device_initcall(ftrace_plt_init
);
197 #endif /* CONFIG_MODULES */
199 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
201 * Hook the return address and push it in the stack of return addresses
202 * in current thread info.
204 unsigned long prepare_ftrace_return(unsigned long parent
, unsigned long ip
)
206 if (unlikely(ftrace_graph_is_dead()))
208 if (unlikely(atomic_read(¤t
->tracing_graph_pause
)))
210 ip
-= MCOUNT_INSN_SIZE
;
211 if (!function_graph_enter(parent
, ip
, 0, NULL
))
212 parent
= (unsigned long) return_to_handler
;
216 NOKPROBE_SYMBOL(prepare_ftrace_return
);
219 * Patch the kernel code at ftrace_graph_caller location. The instruction
220 * there is branch relative on condition. To enable the ftrace graph code
221 * block, we simply patch the mask field of the instruction to zero and
222 * turn the instruction into a nop.
223 * To disable the ftrace graph code the mask field will be patched to
224 * all ones, which turns the instruction into an unconditional branch.
226 int ftrace_enable_ftrace_graph_caller(void)
228 u8 op
= 0x04; /* set mask field to zero */
230 s390_kernel_write(__va(ftrace_graph_caller
)+1, &op
, sizeof(op
));
234 int ftrace_disable_ftrace_graph_caller(void)
236 u8 op
= 0xf4; /* set mask field to all ones */
238 s390_kernel_write(__va(ftrace_graph_caller
)+1, &op
, sizeof(op
));
242 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */