1/*
  2 * Copyright (C) 2008 Imagination Technologies Ltd.
  3 * Licensed under the GPL
  4 *
  5 * Dynamic ftrace support.
  6 */
  7
  8#include <linux/ftrace.h>
  9#include <linux/io.h>
 10#include <linux/uaccess.h>
 11
 12#include <asm/cacheflush.h>
 13
 14#define D04_MOVT_TEMPLATE	0x02200005
 15#define D04_CALL_TEMPLATE	0xAC200005
 16#define D1RTP_MOVT_TEMPLATE	0x03200005
 17#define D1RTP_CALL_TEMPLATE	0xAC200006
 18
 19static const unsigned long NOP[2] = {0xa0fffffe, 0xa0fffffe};
 20static unsigned long movt_and_call_insn[2];
 21
 22static unsigned char *ftrace_nop_replace(void)
 23{
 24	return (char *)&NOP[0];
 25}
 26
 27static unsigned char *ftrace_call_replace(unsigned long pc, unsigned long addr)
 28{
 29	unsigned long hi16, low16;
 30
 31	hi16 = (addr & 0xffff0000) >> 13;
 32	low16 = (addr & 0x0000ffff) << 3;
 33
 34	/*
 35	 * The compiler makes the call to mcount_wrapper()
 36	 * (Meta's wrapper around mcount()) through the register
 37	 * D0.4. So whenever we're patching one of those compiler-generated
 38	 * calls we also need to go through D0.4. Otherwise use D1RtP.
 39	 */
 40	if (pc == (unsigned long)&ftrace_call) {
 41		writel(D1RTP_MOVT_TEMPLATE | hi16, &movt_and_call_insn[0]);
 42		writel(D1RTP_CALL_TEMPLATE | low16, &movt_and_call_insn[1]);
 43	} else {
 44		writel(D04_MOVT_TEMPLATE | hi16, &movt_and_call_insn[0]);
 45		writel(D04_CALL_TEMPLATE | low16, &movt_and_call_insn[1]);
 46	}
 47
 48	return (unsigned char *)&movt_and_call_insn[0];
 49}
 50
 51static int ftrace_modify_code(unsigned long pc, unsigned char *old_code,
 52			      unsigned char *new_code)
 53{
 54	unsigned char replaced[MCOUNT_INSN_SIZE];
 55
 56	/*
 57	 * Note:
 58	 * We are paranoid about modifying text, as if a bug was to happen, it
 59	 * could cause us to read or write to someplace that could cause harm.
 60	 * Carefully read and modify the code with probe_kernel_*(), and make
 61	 * sure what we read is what we expected it to be before modifying it.
 62	 */
 63
 64	/* read the text we want to modify */
 65	if (probe_kernel_read(replaced, (void *)pc, MCOUNT_INSN_SIZE))
 66		return -EFAULT;
 67
 68	/* Make sure it is what we expect it to be */
 69	if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
 70		return -EINVAL;
 71
 72	/* replace the text with the new text */
 73	if (probe_kernel_write((void *)pc, new_code, MCOUNT_INSN_SIZE))
 74		return -EPERM;
 75
 76	flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
 77
 78	return 0;
 79}
 80
 81int ftrace_update_ftrace_func(ftrace_func_t func)
 82{
 83	int ret;
 84	unsigned long pc;
 85	unsigned char old[MCOUNT_INSN_SIZE], *new;
 86
 87	pc = (unsigned long)&ftrace_call;
 88	memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
 89	new = ftrace_call_replace(pc, (unsigned long)func);
 90	ret = ftrace_modify_code(pc, old, new);
 91
 92	return ret;
 93}
 94
 95int ftrace_make_nop(struct module *mod,
 96		    struct dyn_ftrace *rec, unsigned long addr)
 97{
 98	unsigned char *new, *old;
 99	unsigned long ip = rec->ip;
100
101	old = ftrace_call_replace(ip, addr);
102	new = ftrace_nop_replace();
103
104	return ftrace_modify_code(ip, old, new);
105}
106
107int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
108{
109	unsigned char *new, *old;
110	unsigned long ip = rec->ip;
111
112	old = ftrace_nop_replace();
113	new = ftrace_call_replace(ip, addr);
114
115	return ftrace_modify_code(ip, old, new);
116}
117
118/* run from kstop_machine */
119int __init ftrace_dyn_arch_init(void)
120{
121	return 0;
122}