2 * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
3 * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
5 * Code for replacing ftrace calls with jumps.
7 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
9 * Thanks goes to Ingo Molnar, for suggesting the idea.
10 * Mathieu Desnoyers, for suggesting postponing the modifications.
11 * Arjan van de Ven, for keeping me straight, and explaining to me
12 * the dangers of modifying code on the run.
14 #include <linux/uaccess.h>
15 #include <linux/ftrace.h>
16 #include <linux/string.h>
17 #include <linux/init.h>
19 #include <asm/ftrace.h>
20 #include <asm/cacheflush.h>
22 static unsigned char ftrace_replaced_code
[MCOUNT_INSN_SIZE
];
24 static unsigned char ftrace_nop
[4];
26 * If we're trying to nop out a call to a function, we instead
27 * place a call to the address after the memory table.
30 * 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1
31 * 8c011062: 22 4f sts.l pr,@-r15
32 * 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0
33 * 8c011066: 2b 41 jmp @r1
34 * 8c011068: 2a 40 lds r0,pr
36 * 8c01106c: 68 24 .word 0x2468 <--- ip
37 * 8c01106e: 1d 8c .word 0x8c1d
38 * 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE
40 * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
41 * past the _mcount call and continue executing code like normal.
43 static unsigned char *ftrace_nop_replace(unsigned long ip
)
45 __raw_writel(ip
+ MCOUNT_INSN_SIZE
, ftrace_nop
);
49 static unsigned char *ftrace_call_replace(unsigned long ip
, unsigned long addr
)
51 /* Place the address in the memory table. */
52 __raw_writel(addr
, ftrace_replaced_code
);
55 * No locking needed, this must be called via kstop_machine
56 * which in essence is like running on a uniprocessor machine.
58 return ftrace_replaced_code
;
61 static int ftrace_modify_code(unsigned long ip
, unsigned char *old_code
,
62 unsigned char *new_code
)
64 unsigned char replaced
[MCOUNT_INSN_SIZE
];
67 * Note: Due to modules and __init, code can
68 * disappear and change, we need to protect against faulting
69 * as well as code changing. We do this by using the
70 * probe_kernel_* functions.
72 * No real locking needed, this code is run through
73 * kstop_machine, or before SMP starts.
76 /* read the text we want to modify */
77 if (probe_kernel_read(replaced
, (void *)ip
, MCOUNT_INSN_SIZE
))
80 /* Make sure it is what we expect it to be */
81 if (memcmp(replaced
, old_code
, MCOUNT_INSN_SIZE
) != 0)
84 /* replace the text with the new text */
85 if (probe_kernel_write((void *)ip
, new_code
, MCOUNT_INSN_SIZE
))
88 flush_icache_range(ip
, ip
+ MCOUNT_INSN_SIZE
);
93 int ftrace_update_ftrace_func(ftrace_func_t func
)
95 unsigned long ip
= (unsigned long)(&ftrace_call
) + MCOUNT_INSN_OFFSET
;
96 unsigned char old
[MCOUNT_INSN_SIZE
], *new;
98 memcpy(old
, (unsigned char *)ip
, MCOUNT_INSN_SIZE
);
99 new = ftrace_call_replace(ip
, (unsigned long)func
);
101 return ftrace_modify_code(ip
, old
, new);
104 int ftrace_make_nop(struct module
*mod
,
105 struct dyn_ftrace
*rec
, unsigned long addr
)
107 unsigned char *new, *old
;
108 unsigned long ip
= rec
->ip
;
110 old
= ftrace_call_replace(ip
, addr
);
111 new = ftrace_nop_replace(ip
);
113 return ftrace_modify_code(rec
->ip
, old
, new);
116 int ftrace_make_call(struct dyn_ftrace
*rec
, unsigned long addr
)
118 unsigned char *new, *old
;
119 unsigned long ip
= rec
->ip
;
121 old
= ftrace_nop_replace(ip
);
122 new = ftrace_call_replace(ip
, addr
);
124 return ftrace_modify_code(rec
->ip
, old
, new);
127 int __init
ftrace_dyn_arch_init(void *data
)
129 /* The return code is retured via data */
130 __raw_writel(0, (unsigned long)data
);