[PATCH 2/2] ftrace: add function-graph tracer support for ARM v2

[Tim Bird]

Add ftrace function-graph tracer support for ARM.

This includes adding code in mcount to check for
(and call) a registered function graph trace entry
routine, and adding infrastructure to support a return
trampoline to the threadinfo structure.

The code in arch/arm/kernel/ftrace_return.c was
cloned from arch/x86/kernel/ftrace.c

IRQENTRY_TEXT was added to vmlinux.lds.S (to eliminate
a compiler error on kernel/trace/trace_functions_graph.c),
although no routines were marked as __irq_entry.

This works for me with a gcc 4.1.1 compiler on an
OMAP OSK board.  This is against -tip (or at least,
-tip a few weeks ago - 2.6.30-rc3)

This (v2) patch addresses previously received feedback,
except for one issue.  In this version of the code,
a function_graph tracer overrides regular function
tracers.  I'll try to address that in a subsequent
patch, but I didn't want to go too long without posting
something.

Note: this code is much cleaner now that much of the
common return-handling code was moved into
kernel/trace_functions_graph.c

Signed-off-by: Tim Bird <tim.bird@xxxxxxxxxxx>
---
 arch/arm/Kconfig                |    1
 arch/arm/kernel/Makefile        |    4 +--
 arch/arm/kernel/entry-common.S  |   34 ++++++++++++++++++++++++++++++
 arch/arm/kernel/ftrace_return.c |   44 ++++++++++++++++++++++++++++++++++++++++
 arch/arm/kernel/vmlinux.lds.S   |    1
 5 files changed, 81 insertions(+), 3 deletions(-)

--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -17,6 +17,7 @@ config ARM
 	select HAVE_KPROBES if (!XIP_KERNEL)
 	select HAVE_KRETPROBES if (HAVE_KPROBES)
 	select HAVE_FUNCTION_TRACER if (!XIP_KERNEL)
+	select HAVE_FUNCTION_GRAPH_TRACER if (!XIP_KERNEL)
 	select HAVE_GENERIC_DMA_COHERENT
 	help
 	  The ARM series is a line of low-power-consumption RISC chip designs
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -4,9 +4,8 @@

 AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET)

-ifdef CONFIG_DYNAMIC_FTRACE
 CFLAGS_REMOVE_ftrace.o = -pg
-endif
+CFLAGS_REMOVE_ftrace_return.o = -pg

 # Object file lists.

@@ -23,6 +22,7 @@ obj-$(CONFIG_ISA_DMA)		+= dma-isa.o
 obj-$(CONFIG_PCI)		+= bios32.o isa.o
 obj-$(CONFIG_SMP)		+= smp.o
 obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o
+obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+= ftrace_return.o
 obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o
 obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes-decode.o
 obj-$(CONFIG_ATAGS_PROC)	+= atags.o
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -112,6 +112,11 @@ ENTRY(mcount)
 	mov r0, lr
 	sub r0, r0, #MCOUNT_INSN_SIZE

+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	@ FIXTHIS - DYNAMIC_FTRACE does not support function graph tracing
+	@ when the dynamic work is revived, this should be supported as well
+#endif
+
 	.globl mcount_call
 mcount_call:
 	bl ftrace_stub
@@ -139,8 +144,16 @@ ENTRY(mcount)
 	adr r0, ftrace_stub
 	cmp r0, r2
 	bne trace
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	ldr r1, =ftrace_graph_return
+	ldr r2, [r1]
+	cmp r0, r2		@ if *ftrace_graph_return != ftrace_stub
+	bne ftrace_graph_caller
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
 	ldr lr, [fp, #-4]			@ restore lr
-	ldmia sp!, {r0-r3, pc}
+	ldmia sp!, {r0-r3, pc}			@ return doing nothing

 trace:
 	ldr r1, [fp, #-4]			@ lr of instrumented routine
@@ -151,6 +164,25 @@ trace:
 	mov lr, r1				@ restore lr
 	ldmia sp!, {r0-r3, pc}

+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ENTRY(ftrace_graph_caller)
+	sub r0, fp, #4			@ &lr of instrumented routine (&parent)
+	mov r1, lr			@ instrumented routine (func)
+	sub r1, r1, #MCOUNT_INSN_SIZE
+	bl prepare_ftrace_return
+	ldr lr, [fp, #-4]		@ restore lr
+	ldmia sp!, {r0-r3, pc}
+
+	.globl return_to_handler
+return_to_handler:
+	stmdb sp!, {r0-r3}
+	bl ftrace_return_to_handler
+	mov lr, r0			@ r0 has real ret addr
+	ldmia sp!, {r0-r3}
+	mov pc, lr
+
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
 #endif /* CONFIG_DYNAMIC_FTRACE */

 	.globl ftrace_stub
--- /dev/null
+++ b/arch/arm/kernel/ftrace_return.c
@@ -0,0 +1,44 @@
+/*
+ * function return tracing support.
+ *
+ * Copyright (C) 2009 Tim Bird <tim.bird@xxxxxxxxxxx>
+ *
+ * For licencing details, see COPYING.
+ *
+ * Defines routine needed for ARM return trampoline for tracing
+ * function exits.
+ */
+
+#include <linux/ftrace.h>
+
+/*
+ * Hook the return address and push it in the stack of return addrs
+ * in current thread info.
+ */
+void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
+{
+	unsigned long old;
+
+	struct ftrace_graph_ent trace;
+	unsigned long return_hooker = (unsigned long)
+				&return_to_handler;
+
+	if (unlikely(atomic_read(&current->tracing_graph_pause)))
+		return;
+
+	old = *parent;
+	*parent = return_hooker;
+
+	if (ftrace_push_return_trace(old, self_addr, &trace.depth) == -EBUSY) {
+		*parent = old;
+		return;
+	}
+
+	trace.func = self_addr;
+
+	/* Only trace if the calling function expects to */
+	if (!ftrace_graph_entry(&trace)) {
+		current->curr_ret_stack--;
+		*parent = old;
+	}
+}
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -99,6 +99,7 @@ SECTIONS
 			SCHED_TEXT
 			LOCK_TEXT
 			KPROBES_TEXT
+			IRQENTRY_TEXT
 #ifdef CONFIG_MMU
 			*(.fixup)
 #endif

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