[PATCH] Add function graph tracer support for ARM (resend)

From: Tim Bird
Date: Thu Apr 23 2009 - 14:36:48 EST

My first post of this wasn't wide enough. Now adding the
linux-arm-kernel list and a few more CC:s. Sorry if you
get this twice.

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 the threadinfo
structure to support a return trampoline.

I wrote a separate program to scan the kernel assembly
output and validate that callframes for mcount are
generated properly. (It's available upon request for
anyone interested.)

Much of the code in arch/arm/kernel/ftrace.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.

FIXTHIS indicates questions or areas of uncertainty.

This works for me with a gcc 4.1.1 compiler (EABI with
frame pointers turned on) on an OMAP OSK board, with
kernel 2.6.29.

The use of "already_here" works around trace entry nesting
(I believe due to instrumentation of either cpu_clock or
raw_smp_processor_id). Advice on the best way to deal
with this would be appreciated. (that is, whether
to use the guard variable, or just un-instrument the
offending routines).

Thanks for any feedback.

Signed-off-by: <tim.bird@xxxxxxxxxxx>
---
arch/arm/Kconfig | 1
arch/arm/include/asm/ftrace.h | 28 +++++++
arch/arm/kernel/Makefile | 3
arch/arm/kernel/entry-common.S | 29 +++++++-
arch/arm/kernel/ftrace.c | 146 +++++++++++++++++++++++++++++++++++++++++
arch/arm/kernel/vmlinux.lds.S | 1
6 files changed, 204 insertions(+), 4 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/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -7,8 +7,32 @@

#ifndef __ASSEMBLY__
extern void mcount(void);
-#endif
+#endif /* __ASSEMBLY__ */

-#endif
+#endif /* CONFIG_FUNCTION_TRACER */
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+#ifndef __ASSEMBLY__
+
+/*
+ * Stack of return addresses for functions of a thread.
+ * Used in struct thread_info
+ */
+struct ftrace_ret_stack {
+ unsigned long ret;
+ unsigned long func;
+ unsigned long long calltime;
+};
+
+/*
+ * Primary handler of a function return.
+ * It relays on ftrace_return_to_handler.
+ * Defined in entry-common.S
+ */
+extern void return_to_handler(void);
+
+#endif /* __ASSEMBLY__ */
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

#endif /* _ASM_ARM_FTRACE */
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -4,7 +4,7 @@

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

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

@@ -23,6 +23,7 @@ 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-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
obj-$(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
@@ -135,8 +135,16 @@ 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
@@ -147,6 +155,25 @@ 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
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -16,6 +16,8 @@
#include <asm/cacheflush.h>
#include <asm/ftrace.h>

+#ifdef CONFIG_DYNAMIC_FTRACE
+
#define PC_OFFSET 8
#define BL_OPCODE 0xeb000000
#define BL_OFFSET_MASK 0x00ffffff
@@ -101,3 +103,147 @@ int __init ftrace_dyn_arch_init(void *da
ftrace_mcount_set(data);
return 0;
}
+
+#endif /* CONFIG_DYNAMIC_FTRACE */
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+/* Add a function return address to the trace stack on thread info.*/
+static int push_return_trace(unsigned long ret, unsigned long long time,
+ unsigned long func, int *depth)
+{
+ int index;
+
+ if (!current->ret_stack)
+ return -EBUSY;
+
+ /* The return trace stack is full */
+ if (current->curr_ret_stack == FTRACE_RETFUNC_DEPTH - 1) {
+ atomic_inc(&current->trace_overrun);
+ return -EBUSY;
+ }
+
+ index = ++current->curr_ret_stack;
+ barrier();
+ current->ret_stack[index].ret = ret;
+ current->ret_stack[index].func = func;
+ current->ret_stack[index].calltime = time;
+ *depth = index;
+
+ return 0;
+}
+
+/*
+ * Retrieve a function return address from the trace stack on thread info.
+ * set the address to return to in *ret
+ */
+static void pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret)
+{
+ int index;
+
+ index = current->curr_ret_stack;
+
+ if (unlikely(index < 0)) {
+ ftrace_graph_stop();
+ WARN_ON(1);
+ /* Might as well panic, otherwise we have no where to go */
+ *ret = (unsigned long)panic;
+ return;
+ }
+
+ *ret = current->ret_stack[index].ret;
+ trace->func = current->ret_stack[index].func;
+ trace->calltime = current->ret_stack[index].calltime;
+ trace->overrun = atomic_read(&current->trace_overrun);
+ trace->depth = index;
+ barrier();
+ current->curr_ret_stack--;
+}
+
+int already_here; /* starts at 0 */
+
+/*
+ * Send the trace to the ring-buffer
+ * @return the original return address
+ */
+unsigned long ftrace_return_to_handler(void)
+{
+ struct ftrace_graph_ret trace;
+ unsigned long ret;
+
+ /* guard against trace entry while handling a trace exit */
+ already_here++;
+
+ pop_return_trace(&trace, &ret);
+ trace.rettime = cpu_clock(raw_smp_processor_id());
+ ftrace_graph_return(&trace);
+
+ if (unlikely(!ret)) {
+ ftrace_graph_stop();
+ WARN_ON(1);
+ /* Might as well panic. Where else to go? */
+ ret = (unsigned long)panic;
+ }
+
+ already_here--;
+ return ret;
+}
+
+/*
+ * 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;
+ unsigned long long calltime;
+
+ struct ftrace_graph_ent trace;
+ unsigned long return_hooker = (unsigned long)
+ &return_to_handler;
+
+ if (already_here)
+ return;
+ already_here++;
+
+ if (unlikely(atomic_read(&current->tracing_graph_pause))) {
+ already_here--;
+ return;
+ }
+
+ /* FIXTHIS - need a local_irqsave here?, (to fend off ints?) */
+
+ /* FIXTHIS - x86 protects against a fault during this operation!*/
+ old = *parent;
+ *parent = return_hooker;
+
+ if (unlikely(!__kernel_text_address(old))) {
+ ftrace_graph_stop();
+ *parent = old;
+ WARN_ON(1);
+ already_here--;
+ return;
+ }
+
+ /* FIXTHIS - trace entry appears to nest inside following */
+ calltime = cpu_clock(raw_smp_processor_id());
+
+ if (push_return_trace(old, calltime,
+ self_addr, &trace.depth) == -EBUSY) {
+ *parent = old;
+ already_here--;
+ return;
+ }
+
+ trace.func = self_addr;
+
+ /* Only trace if the calling function expects to */
+ if (!ftrace_graph_entry(&trace)) {
+ current->curr_ret_stack--;
+ *parent = old;
+ }
+
+ already_here--;
+}
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -95,6 +95,7 @@ SECTIONS
SCHED_TEXT
LOCK_TEXT
KPROBES_TEXT
+ IRQENTRY_TEXT
#ifdef CONFIG_MMU
*(.fixup)
#endif

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