sh: dynamic ftrace support.

First cut at dynamic ftrace support.

Signed-off-by: Matt Fleming <mjf@gentoo.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 109 insertions, 0 deletions

diff --git a/arch/sh/kernel/ftrace.c b/arch/sh/kernel/ftrace.c
new file mode 100644
index 000000000000..6c193d56c2e7
--- /dev/null
+++ b/arch/sh/kernel/ftrace.c
@@ -0,0 +1,109 @@
+/*
+ * Copyright (C) 2008 Matt Fleming <mjf@gentoo.org>
+ *
+ * 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/uaccess.h>
+#include <linux/ftrace.h>
+#include <linux/string.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <asm/ftrace.h>
+#include <asm/cacheflush.h>
+
+static unsigned char ftrace_nop[] = {
+        0x09, 0x00,             /* nop */
+        0x09, 0x00,             /* nop */
+};
+
+static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];
+
+unsigned char *ftrace_nop_replace(void)
+{
+        return ftrace_nop;
+}
+
+static int is_sh_nop(unsigned char *ip)
+{
+        return strncmp(ip, ftrace_nop, sizeof(ftrace_nop));
+}
+
+unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
+{
+        /* Place the address in the memory table. */
+        if (addr == CALLER_ADDR)
+                __raw_writel(addr + MCOUNT_INSN_OFFSET, ftrace_replaced_code);
+        else
+                __raw_writel(addr, ftrace_replaced_code);
+
+        /*
+         * No locking needed, this must be called via kstop_machine
+         * which in essence is like running on a uniprocessor machine.
+         */
+        return ftrace_replaced_code;
+}
+
+int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
+                       unsigned char *new_code)
+{
+        unsigned char replaced[MCOUNT_INSN_SIZE];
+
+        /*
+         * Note: Due to modules and __init, code can
+         *  disappear and change, we need to protect against faulting
+         *  as well as code changing. We do this by using the
+         *  probe_kernel_* functions.
+         *
+         * No real locking needed, this code is run through
+         * kstop_machine, or before SMP starts.
+         */
+
+        /*
+         * If we're trying to nop out a call to a function, we instead
+         * place a call to the address after the memory table.
+         */
+        if (is_sh_nop(new_code) == 0)
+                __raw_writel(ip + MCOUNT_INSN_SIZE, (unsigned long)new_code);
+
+        /* read the text we want to modify */
+        if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+                return -EFAULT;
+
+        /* Make sure it is what we expect it to be */
+        if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
+                return -EINVAL;
+
+        /* replace the text with the new text */
+        if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
+                return -EPERM;
+
+        flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
+
+        return 0;
+}
+
+int ftrace_update_ftrace_func(ftrace_func_t func)
+{
+        unsigned long ip = (unsigned long)(&ftrace_call);
+        unsigned char old[MCOUNT_INSN_SIZE], *new;
+
+        memcpy(old, (unsigned char *)(ip + MCOUNT_INSN_OFFSET), MCOUNT_INSN_SIZE);
+        new = ftrace_call_replace(ip, (unsigned long)func);
+
+        return ftrace_modify_code(ip + MCOUNT_INSN_OFFSET, old, new);
+}
+
+int __init ftrace_dyn_arch_init(void *data)
+{
+        /* The return code is retured via data */
+        __raw_writel(0, (unsigned long)data);
+
+        return 0;
+}