134 lines
3.8 KiB
C
134 lines
3.8 KiB
C
/*
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* Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
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* Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
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*
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* Code for replacing ftrace calls with jumps.
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*
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* Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
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*
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* Thanks goes to Ingo Molnar, for suggesting the idea.
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* Mathieu Desnoyers, for suggesting postponing the modifications.
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* Arjan van de Ven, for keeping me straight, and explaining to me
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* the dangers of modifying code on the run.
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*/
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#include <linux/uaccess.h>
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#include <linux/ftrace.h>
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#include <linux/string.h>
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#include <linux/init.h>
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#include <linux/io.h>
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#include <asm/ftrace.h>
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#include <asm/cacheflush.h>
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static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
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static unsigned char ftrace_nop[4];
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/*
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* If we're trying to nop out a call to a function, we instead
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* place a call to the address after the memory table.
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*
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* 8c011060 <a>:
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* 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1
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* 8c011062: 22 4f sts.l pr,@-r15
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* 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0
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* 8c011066: 2b 41 jmp @r1
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* 8c011068: 2a 40 lds r0,pr
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* 8c01106a: 09 00 nop
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* 8c01106c: 68 24 .word 0x2468 <--- ip
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* 8c01106e: 1d 8c .word 0x8c1d
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* 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE
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*
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* We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
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* past the _mcount call and continue executing code like normal.
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*/
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static unsigned char *ftrace_nop_replace(unsigned long ip)
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{
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__raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
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return ftrace_nop;
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}
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static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
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{
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/* Place the address in the memory table. */
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__raw_writel(addr, ftrace_replaced_code);
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/*
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* No locking needed, this must be called via kstop_machine
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* which in essence is like running on a uniprocessor machine.
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*/
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return ftrace_replaced_code;
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}
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static int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
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unsigned char *new_code)
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{
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unsigned char replaced[MCOUNT_INSN_SIZE];
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/*
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* Note: Due to modules and __init, code can
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* disappear and change, we need to protect against faulting
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* as well as code changing. We do this by using the
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* probe_kernel_* functions.
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*
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* No real locking needed, this code is run through
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* kstop_machine, or before SMP starts.
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*/
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/* read the text we want to modify */
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if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
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return -EFAULT;
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/* Make sure it is what we expect it to be */
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if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
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return -EINVAL;
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/* replace the text with the new text */
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if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
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return -EPERM;
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flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
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return 0;
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}
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int ftrace_update_ftrace_func(ftrace_func_t func)
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{
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unsigned long ip = (unsigned long)(&ftrace_call) + MCOUNT_INSN_OFFSET;
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unsigned char old[MCOUNT_INSN_SIZE], *new;
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memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
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new = ftrace_call_replace(ip, (unsigned long)func);
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return ftrace_modify_code(ip, old, new);
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}
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int ftrace_make_nop(struct module *mod,
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struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned char *new, *old;
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unsigned long ip = rec->ip;
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old = ftrace_call_replace(ip, addr);
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new = ftrace_nop_replace(ip);
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return ftrace_modify_code(rec->ip, old, new);
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}
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int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned char *new, *old;
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unsigned long ip = rec->ip;
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old = ftrace_nop_replace(ip);
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new = ftrace_call_replace(ip, addr);
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return ftrace_modify_code(rec->ip, old, new);
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}
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int __init ftrace_dyn_arch_init(void *data)
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{
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/* The return code is retured via data */
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__raw_writel(0, (unsigned long)data);
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return 0;
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}
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