/* * 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> #include <asm/ftrace.h> #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 + PC_OFFSET); if (unlikely(offset < -33554432 || offset > 33554428)) { /* Can't generate branches that far (from ARM ARM). Ftrace * doesn't generate branches outside of 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; __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 + MCOUNT_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; memcpy(&old, &ftrace_call, MCOUNT_INSN_SIZE); new = ftrace_call_replace(pc, (unsigned long)func); ret = ftrace_modify_code(pc, (unsigned char *)&old, new); return ret; } /* run from ftrace_init with irqs disabled */ int __init ftrace_dyn_arch_init(void *data) { ftrace_mcount_set(data); return 0; }