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-rw-r--r--arch/x86/kernel/ftrace.c141
1 files changed, 141 insertions, 0 deletions
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
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+++ b/arch/x86/kernel/ftrace.c
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+/*
+ * Code for replacing ftrace calls with jumps.
+ *
+ * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
+ *
+ * Thanks goes to Ingo Molnar, for suggesting the idea.
+ * Mathieu Desnoyers, for suggesting postponing the modifications.
+ * Arjan van de Ven, for keeping me straight, and explaining to me
+ * the dangers of modifying code on the run.
+ */
+
+#include <linux/spinlock.h>
+#include <linux/hardirq.h>
+#include <linux/ftrace.h>
+#include <linux/percpu.h>
+#include <linux/init.h>
+#include <linux/list.h>
+
+#include <asm/alternative.h>
+#include <asm/ftrace.h>
+
+
+/* Long is fine, even if it is only 4 bytes ;-) */
+static long *ftrace_nop;
+
+union ftrace_code_union {
+ char code[MCOUNT_INSN_SIZE];
+ struct {
+ char e8;
+ int offset;
+ } __attribute__((packed));
+};
+
+
+static int notrace ftrace_calc_offset(long ip, long addr)
+{
+ return (int)(addr - ip);
+}
+
+notrace unsigned char *ftrace_nop_replace(void)
+{
+ return (char *)ftrace_nop;
+}
+
+notrace unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
+{
+ static union ftrace_code_union calc;
+
+ calc.e8 = 0xe8;
+ calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);
+
+ /*
+ * No locking needed, this must be called via kstop_machine
+ * which in essence is like running on a uniprocessor machine.
+ */
+ return calc.code;
+}
+
+notrace int
+ftrace_modify_code(unsigned long ip, unsigned char *old_code,
+ unsigned char *new_code)
+{
+ unsigned replaced;
+ unsigned old = *(unsigned *)old_code; /* 4 bytes */
+ unsigned new = *(unsigned *)new_code; /* 4 bytes */
+ unsigned char newch = new_code[4];
+ int faulted = 0;
+
+ /*
+ * Note: Due to modules and __init, code can
+ * disappear and change, we need to protect against faulting
+ * as well as code changing.
+ *
+ * No real locking needed, this code is run through
+ * kstop_machine.
+ */
+ asm volatile (
+ "1: lock\n"
+ " cmpxchg %3, (%2)\n"
+ " jnz 2f\n"
+ " movb %b4, 4(%2)\n"
+ "2:\n"
+ ".section .fixup, \"ax\"\n"
+ "3: movl $1, %0\n"
+ " jmp 2b\n"
+ ".previous\n"
+ _ASM_EXTABLE(1b, 3b)
+ : "=r"(faulted), "=a"(replaced)
+ : "r"(ip), "r"(new), "c"(newch),
+ "0"(faulted), "a"(old)
+ : "memory");
+ sync_core();
+
+ if (replaced != old && replaced != new)
+ faulted = 2;
+
+ return faulted;
+}
+
+notrace int ftrace_update_ftrace_func(ftrace_func_t func)
+{
+ unsigned long ip = (unsigned long)(&ftrace_call);
+ unsigned char old[MCOUNT_INSN_SIZE], *new;
+ int ret;
+
+ memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
+ new = ftrace_call_replace(ip, (unsigned long)func);
+ ret = ftrace_modify_code(ip, old, new);
+
+ return ret;
+}
+
+notrace int ftrace_mcount_set(unsigned long *data)
+{
+ unsigned long ip = (long)(&mcount_call);
+ unsigned long *addr = data;
+ unsigned char old[MCOUNT_INSN_SIZE], *new;
+
+ /*
+ * Replace the mcount stub with a pointer to the
+ * ip recorder function.
+ */
+ memcpy(old, &mcount_call, MCOUNT_INSN_SIZE);
+ new = ftrace_call_replace(ip, *addr);
+ *addr = ftrace_modify_code(ip, old, new);
+
+ return 0;
+}
+
+int __init ftrace_dyn_arch_init(void *data)
+{
+ const unsigned char *const *noptable = find_nop_table();
+
+ /* This is running in kstop_machine */
+
+ ftrace_mcount_set(data);
+
+ ftrace_nop = (unsigned long *)noptable[MCOUNT_INSN_SIZE];
+
+ return 0;
+}
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