microblaze: ftrace: Add dynamic trace support

With dynamic function tracer, by default, _mcount is defined as an
"empty" function, it returns directly without any more action. When
enabling it in user-space, it will jump to a real tracing
function(ftrace_caller), and do the real job for us.

Differ from the static function tracer, dynamic function tracer provides
two functions ftrace_make_call()/ftrace_make_nop() to enable/disable the
tracing of some indicated kernel functions(set_ftrace_filter).

In the kernel version, there is only one "_mcount" string for every
kernel function, so, we just need to match this one in mcount_regex of
scripts/recordmcount.pl.

For more information please look at code and Documentation/trace folder.

Steven ACK that scripts/recordmcount.pl part.

Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Michal Simek <monstr@monstr.eu>

1 files changed, 151 insertions, 0 deletions

diff --git a/arch/microblaze/kernel/ftrace.c b/arch/microblaze/kernel/ftrace.c
new file mode 100644
index 000000000000..c1889b101cb8
--- /dev/null
+++ b/arch/microblaze/kernel/ftrace.c
@@ -0,0 +1,151 @@
+/*
+ * Ftrace support for Microblaze.
+ *
+ * Copyright (C) 2009 Michal Simek <monstr@monstr.eu>
+ * Copyright (C) 2009 PetaLogix
+ *
+ * Based on MIPS and PowerPC ftrace code
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <asm/cacheflush.h>
+#include <linux/ftrace.h>
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+/* save value to addr - it is save to do it in asm */
+static int ftrace_modify_code(unsigned long addr, unsigned int value)
+{
+	int faulted = 0;
+
+	__asm__ __volatile__("	1:	swi	%2, %1, 0;		\
+					addik	%0, r0, 0;		\
+				2:					\
+					.section .fixup, \"ax\";	\
+				3:	brid	2b;			\
+					addik	%0, r0, 1;		\
+					.previous;			\
+					.section __ex_table,\"a\";	\
+					.word	1b,3b;			\
+					.previous;"			\
+				: "=r" (faulted)
+				: "r" (addr), "r" (value)
+	);
+
+	if (unlikely(faulted))
+		return -EFAULT;
+
+	return 0;
+}
+
+#define MICROBLAZE_NOP 0x80000000
+#define MICROBLAZE_BRI 0xb800000C
+
+static unsigned int recorded; /* if save was or not */
+static unsigned int imm; /* saving whole imm instruction */
+
+/* There are two approaches howto solve ftrace_make nop function - look below */
+#undef USE_FTRACE_NOP
+
+#ifdef USE_FTRACE_NOP
+static unsigned int bralid; /* saving whole bralid instruction */
+#endif
+
+int ftrace_make_nop(struct module *mod,
+			struct dyn_ftrace *rec, unsigned long addr)
+{
+	/* we have this part of code which we are working with
+	 * b000c000        imm     -16384
+	 * b9fc8e30        bralid  r15, -29136     // c0008e30 <_mcount>
+	 * 80000000        or      r0, r0, r0
+	 *
+	 * The first solution (!USE_FTRACE_NOP-could be called branch solution)
+	 * b000c000        bri	12 (0xC - jump to any other instruction)
+	 * b9fc8e30        bralid  r15, -29136     // c0008e30 <_mcount>
+	 * 80000000        or      r0, r0, r0
+	 * any other instruction
+	 *
+	 * The second solution (USE_FTRACE_NOP) - no jump just nops
+	 * 80000000        or      r0, r0, r0
+	 * 80000000        or      r0, r0, r0
+	 * 80000000        or      r0, r0, r0
+	 */
+	int ret = 0;
+
+	if (recorded == 0) {
+		recorded = 1;
+		imm = *(unsigned int *)rec->ip;
+		pr_debug("%s: imm:0x%x\n", __func__, imm);
+#ifdef USE_FTRACE_NOP
+		bralid = *(unsigned int *)(rec->ip + 4);
+		pr_debug("%s: bralid 0x%x\n", __func__, bralid);
+#endif /* USE_FTRACE_NOP */
+	}
+
+#ifdef USE_FTRACE_NOP
+	ret = ftrace_modify_code(rec->ip, MICROBLAZE_NOP);
+	ret += ftrace_modify_code(rec->ip + 4, MICROBLAZE_NOP);
+#else /* USE_FTRACE_NOP */
+	ret = ftrace_modify_code(rec->ip, MICROBLAZE_BRI);
+#endif /* USE_FTRACE_NOP */
+	return ret;
+}
+
+static int ret_addr; /* initialized as 0 by default */
+
+/* I believe that first is called ftrace_make_nop before this function */
+int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+{
+	int ret;
+	ret_addr = addr; /* saving where the barrier jump is */
+	pr_debug("%s: addr:0x%x, rec->ip: 0x%x, imm:0x%x\n",
+		__func__, (unsigned int)addr, (unsigned int)rec->ip, imm);
+	ret = ftrace_modify_code(rec->ip, imm);
+#ifdef USE_FTRACE_NOP
+	pr_debug("%s: bralid:0x%x\n", __func__, bralid);
+	ret += ftrace_modify_code(rec->ip + 4, bralid);
+#endif /* USE_FTRACE_NOP */
+	return ret;
+}
+
+int __init ftrace_dyn_arch_init(void *data)
+{
+	/* The return code is retured via data */
+	*(unsigned long *)data = 0;
+
+	return 0;
+}
+
+int ftrace_update_ftrace_func(ftrace_func_t func)
+{
+	unsigned long ip = (unsigned long)(&ftrace_call);
+	unsigned int upper = (unsigned int)func;
+	unsigned int lower = (unsigned int)func;
+	int ret = 0;
+
+	/* create proper saving to ftrace_call poll */
+	upper = 0xb0000000 + (upper >> 16); /* imm func_upper */
+	lower = 0x32800000 + (lower & 0xFFFF); /* addik r20, r0, func_lower */
+
+	pr_debug("%s: func=0x%x, ip=0x%x, upper=0x%x, lower=0x%x\n",
+		__func__, (unsigned int)func, (unsigned int)ip, upper, lower);
+
+	/* save upper and lower code */
+	ret = ftrace_modify_code(ip, upper);
+	ret += ftrace_modify_code(ip + 4, lower);
+
+	/* We just need to remove the rtsd r15, 8 by NOP */
+	BUG_ON(!ret_addr);
+	if (ret_addr)
+		ret += ftrace_modify_code(ret_addr, MICROBLAZE_NOP);
+	else
+		ret = 1; /* fault */
+
+	/* All changes are done - lets do caches consistent */
+	flush_icache();
+	return ret;
+}
+
+#endif /* CONFIG_DYNAMIC_FTRACE */