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