1 files changed, 107 insertions, 48 deletions

diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 0298286ad4ad..f09014cfbf2c 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -2,102 +2,161 @@
  * Dynamic function tracing support.
  *
  * Copyright (C) 2008 Abhishek Sagar <sagar.abhishek@gmail.com>
+ * Copyright (C) 2010 Rabin Vincent <rabin@rab.in>
  *
  * 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.
+ * mcount call-sites get patched with NOP till they are enabled.
+ * All code mutation routines here are called under stop_machine().
  */
 
 #include <linux/ftrace.h>
+#include <linux/uaccess.h>
 
 #include <asm/cacheflush.h>
 #include <asm/ftrace.h>
 
-#define PC_OFFSET      8
-#define BL_OPCODE      0xeb000000
-#define BL_OFFSET_MASK 0x00ffffff
+#define	NOP		0xe8bd4000	/* pop {lr} */
 
-static unsigned long bl_insn;
-static const unsigned long NOP = 0xe1a00000; /* mov r0, r0 */
+#ifdef CONFIG_OLD_MCOUNT
+#define OLD_MCOUNT_ADDR	((unsigned long) mcount)
+#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
 
-unsigned char *ftrace_nop_replace(void)
+#define	OLD_NOP		0xe1a00000	/* mov r0, r0 */
+
+static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
+{
+	return rec->arch.old_mcount ? OLD_NOP : NOP;
+}
+
+static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
+{
+	if (!rec->arch.old_mcount)
+		return addr;
+
+	if (addr == MCOUNT_ADDR)
+		addr = OLD_MCOUNT_ADDR;
+	else if (addr == FTRACE_ADDR)
+		addr = OLD_FTRACE_ADDR;
+
+	return addr;
+}
+#else
+static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
+{
+	return NOP;
+}
+
+static unsigned long adjust_address(struct dyn_ftrace *rec, unsigned long addr)
 {
-	return (char *)&NOP;
+	return addr;
 }
+#endif
 
 /* construct a branch (BL) instruction to addr */
-unsigned char *ftrace_call_replace(unsigned long pc, unsigned long addr)
+static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
 {
 	long offset;
 
-	offset = (long)addr - (long)(pc + PC_OFFSET);
+	offset = (long)addr - (long)(pc + 8);
 	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;
+		return 0;
 	}
-	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;
+	offset = (offset >> 2) & 0x00ffffff;
 
-	old = *(unsigned long *)old_code;
-	new = *(unsigned long *)new_code;
+	return 0xeb000000 | offset;
+}
 
-	__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"
+static int ftrace_modify_code(unsigned long pc, unsigned long old,
+			      unsigned long new)
+{
+	unsigned long replaced;
 
-		".pushsection .fixup, \"ax\"\n"
-		"4:  mov  %0, #1  \n"
-		"    b    3b      \n"
-		".popsection\n"
+	if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
+		return -EFAULT;
 
-		".pushsection __ex_table, \"a\"\n"
-		"    .long 1b, 4b \n"
-		"    .long 2b, 4b \n"
-		".popsection\n"
+	if (replaced != old)
+		return -EINVAL;
 
-		: "=r"(err), "=r"(replaced)
-		: "r"(pc), "r"(new), "r"(old), "0"(err), "1"(replaced)
-		: "memory");
+	if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
+		return -EPERM;
 
-	if (!err && (replaced == old))
-		flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
+	flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
 
-	return err;
+	return 0;
 }
 
 int ftrace_update_ftrace_func(ftrace_func_t func)
 {
-	int ret;
 	unsigned long pc, old;
-	unsigned char *new;
+	unsigned long new;
+	int ret;
 
 	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);
+
+	ret = ftrace_modify_code(pc, old, new);
+
+#ifdef CONFIG_OLD_MCOUNT
+	if (!ret) {
+		pc = (unsigned long)&ftrace_call_old;
+		memcpy(&old, &ftrace_call_old, MCOUNT_INSN_SIZE);
+		new = ftrace_call_replace(pc, (unsigned long)func);
+
+		ret = ftrace_modify_code(pc, old, new);
+	}
+#endif
+
+	return ret;
+}
+
+int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+{
+	unsigned long new, old;
+	unsigned long ip = rec->ip;
+
+	old = ftrace_nop_replace(rec);
+	new = ftrace_call_replace(ip, adjust_address(rec, addr));
+
+	return ftrace_modify_code(rec->ip, old, new);
+}
+
+int ftrace_make_nop(struct module *mod,
+		    struct dyn_ftrace *rec, unsigned long addr)
+{
+	unsigned long ip = rec->ip;
+	unsigned long old;
+	unsigned long new;
+	int ret;
+
+	old = ftrace_call_replace(ip, adjust_address(rec, addr));
+	new = ftrace_nop_replace(rec);
+	ret = ftrace_modify_code(ip, old, new);
+
+#ifdef CONFIG_OLD_MCOUNT
+	if (ret == -EINVAL && addr == MCOUNT_ADDR) {
+		rec->arch.old_mcount = true;
+
+		old = ftrace_call_replace(ip, adjust_address(rec, addr));
+		new = ftrace_nop_replace(rec);
+		ret = ftrace_modify_code(ip, old, new);
+	}
+#endif
+
 	return ret;
 }
 
-/* run from ftrace_init with irqs disabled */
 int __init ftrace_dyn_arch_init(void *data)
 {
-	ftrace_mcount_set(data);
+	*(unsigned long *)data = 0;
+
 	return 0;
 }