mirror of
https://github.com/torvalds/linux
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0a37605c22
x86 now sets up the mcount locations through the build and no longer needs to record the ip when the function is executed. This patch changes the initial mcount to simply return. There's no need to do any other work. If the ftrace start up test fails, the original mcount will be what everything will use, so having this as fast as possible is a good thing. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
132 lines
2.8 KiB
C
132 lines
2.8 KiB
C
/*
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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/spinlock.h>
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#include <linux/hardirq.h>
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#include <linux/ftrace.h>
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#include <linux/percpu.h>
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#include <linux/init.h>
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#include <linux/list.h>
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#include <asm/alternative.h>
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#include <asm/ftrace.h>
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/* Long is fine, even if it is only 4 bytes ;-) */
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static long *ftrace_nop;
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union ftrace_code_union {
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char code[MCOUNT_INSN_SIZE];
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struct {
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char e8;
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int offset;
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} __attribute__((packed));
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};
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static int notrace ftrace_calc_offset(long ip, long addr)
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{
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return (int)(addr - ip);
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}
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notrace unsigned char *ftrace_nop_replace(void)
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{
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return (char *)ftrace_nop;
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}
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notrace unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
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{
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static union ftrace_code_union calc;
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calc.e8 = 0xe8;
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calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);
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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 calc.code;
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}
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notrace int
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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 replaced;
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unsigned old = *(unsigned *)old_code; /* 4 bytes */
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unsigned new = *(unsigned *)new_code; /* 4 bytes */
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unsigned char newch = new_code[4];
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int faulted = 0;
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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.
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*
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* No real locking needed, this code is run through
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* kstop_machine.
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*/
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asm volatile (
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"1: lock\n"
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" cmpxchg %3, (%2)\n"
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" jnz 2f\n"
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" movb %b4, 4(%2)\n"
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"2:\n"
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".section .fixup, \"ax\"\n"
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"3: movl $1, %0\n"
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" jmp 2b\n"
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".previous\n"
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_ASM_EXTABLE(1b, 3b)
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: "=r"(faulted), "=a"(replaced)
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: "r"(ip), "r"(new), "c"(newch),
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"0"(faulted), "a"(old)
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: "memory");
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sync_core();
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if (replaced != old && replaced != new)
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faulted = 2;
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return faulted;
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}
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notrace int ftrace_update_ftrace_func(ftrace_func_t func)
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{
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unsigned long ip = (unsigned long)(&ftrace_call);
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unsigned char old[MCOUNT_INSN_SIZE], *new;
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int ret;
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memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
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new = ftrace_call_replace(ip, (unsigned long)func);
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ret = ftrace_modify_code(ip, old, new);
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return ret;
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}
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notrace int ftrace_mcount_set(unsigned long *data)
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{
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/* mcount is initialized as a nop */
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*data = 0;
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return 0;
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}
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int __init ftrace_dyn_arch_init(void *data)
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{
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const unsigned char *const *noptable = find_nop_table();
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/* This is running in kstop_machine */
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ftrace_mcount_set(data);
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ftrace_nop = (unsigned long *)noptable[MCOUNT_INSN_SIZE];
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return 0;
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}
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