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/*
* Dynamic function tracing support.
*
* Copyright (C) 2008 Abhishek Sagar <sagar.abhishek@gmail.com>
*
* For licencing details, see COPYING.
*
* Defines low-level handling of mcount calls when the kernel
* is compiled with the -pg flag. When using dynamic ftrace, the
* mcount call-sites get patched lazily with NOP till they are
* enabled. All code mutation routines here take effect atomically.
*/
#include <linux/ftrace.h>
#include <asm/cacheflush.h>
#define INSN_SIZE 4
#define PC_OFFSET 8
#define BL_OPCODE 0xeb000000
#define BL_OFFSET_MASK 0x00ffffff
static unsigned long bl_insn;
static const unsigned long NOP = 0xe1a00000; /* mov r0, r0 */
unsigned char *ftrace_nop_replace(void)
{
return (char *)&NOP;
}
/* construct a branch (BL) instruction to addr */
unsigned char *ftrace_call_replace(unsigned long pc, unsigned long addr)
{
long offset;
offset = (long)addr - (long)(pc - INSN_SIZE + PC_OFFSET);
if (unlikely(offset < -33554432 || offset > 33554428)) {
/* Can't generate branches that far (from ARM ARM). Ftrace
* doesn't generate branches outside of core kernel text.
*/
WARN_ON_ONCE(1);
return NULL;
}
offset = (offset >> 2) & BL_OFFSET_MASK;
bl_insn = BL_OPCODE | offset;
return (unsigned char *)&bl_insn;
}
int ftrace_modify_code(unsigned long pc, unsigned char *old_code,
unsigned char *new_code)
{
unsigned long err = 0, replaced = 0, old, new;
old = *(unsigned long *)old_code;
new = *(unsigned long *)new_code;
pc -= INSN_SIZE;
__asm__ __volatile__ (
"1: ldr %1, [%2] \n"
" cmp %1, %4 \n"
"2: streq %3, [%2] \n"
" cmpne %1, %3 \n"
" movne %0, #2 \n"
"3:\n"
".section .fixup, \"ax\"\n"
"4: mov %0, #1 \n"
" b 3b \n"
".previous\n"
".section __ex_table, \"a\"\n"
" .long 1b, 4b \n"
" .long 2b, 4b \n"
".previous\n"
: "=r"(err), "=r"(replaced)
: "r"(pc), "r"(new), "r"(old), "0"(err), "1"(replaced)
: "memory");
if (!err && (replaced == old))
flush_icache_range(pc, pc + INSN_SIZE);
return err;
}
int ftrace_update_ftrace_func(ftrace_func_t func)
{
int ret;
unsigned long pc, old;
unsigned char *new;
pc = (unsigned long)&ftrace_call;
pc += INSN_SIZE;
memcpy(&old, &ftrace_call, INSN_SIZE);
new = ftrace_call_replace(pc, (unsigned long)func);
ret = ftrace_modify_code(pc, (unsigned char *)&old, new);
return ret;
}
int ftrace_mcount_set(unsigned long *data)
{
unsigned long pc, old;
unsigned long *addr = data;
unsigned char *new;
pc = (unsigned long)&mcount_call;
pc += INSN_SIZE;
memcpy(&old, &mcount_call, INSN_SIZE);
new = ftrace_call_replace(pc, *addr);
*addr = ftrace_modify_code(pc, (unsigned char *)&old, new);
return 0;
}
/* run from kstop_machine */
int __init ftrace_dyn_arch_init(void *data)
{
ftrace_mcount_set(data);
return 0;
}
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