Re: [PATCH v6 6/7] arm64: ftrace: Add CALLER_ADDRx macros

On Thu, Mar 13, 2014 at 10:13:49AM +0000, AKASHI Takahiro wrote:

CALLER_ADDRx returns caller's address at specified level in call stacks. They are used for several tracers like irqsoff and preemptoff. Strange to say, however, they are refered even without FTRACE.

Please note that this implementation assumes that we have frame pointers. (which means kernel should be compiled with -fno-omit-frame-pointer.)

How do you ensure that -fno-omit-frame-pointer is passed?

Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.org

arch/arm64/include/asm/ftrace.h | 13 ++++++++- arch/arm64/kernel/Makefile | 3 +- arch/arm64/kernel/return_address.c | 55 ++++++++++++++++++++++++++++++++++++ 3 files changed, 69 insertions(+), 2 deletions(-) create mode 100644 arch/arm64/kernel/return_address.c

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h index ed5c448..c44c4b1 100644 --- a/arch/arm64/include/asm/ftrace.h +++ b/arch/arm64/include/asm/ftrace.h @@ -18,6 +18,7 @@ #ifndef __ASSEMBLY__ extern void _mcount(unsigned long); +extern void *return_address(unsigned int); struct dyn_arch_ftrace { /* No extra data needed for arm64 */ @@ -33,6 +34,16 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr) */ return addr; } -#endif /* __ASSEMBLY__ */

+#define HAVE_ARCH_CALLER_ADDR

+#define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0)) +#define CALLER_ADDR1 ((unsigned long)return_address(1)) +#define CALLER_ADDR2 ((unsigned long)return_address(2)) +#define CALLER_ADDR3 ((unsigned long)return_address(3)) +#define CALLER_ADDR4 ((unsigned long)return_address(4)) +#define CALLER_ADDR5 ((unsigned long)return_address(5)) +#define CALLER_ADDR6 ((unsigned long)return_address(6))

Could we change the core definitions of these macros (in linux/ftrace.h) to use return_address, then provide an overridable version of return_address that defaults to __builtin_return_address, instead of copy-pasting this sequence?

diff --git a/arch/arm64/kernel/return_address.c b/arch/arm64/kernel/return_address.c new file mode 100644 index 0000000..89102a6 --- /dev/null +++ b/arch/arm64/kernel/return_address.c @@ -0,0 +1,55 @@ +/*

• • arch/arm64/kernel/return_address.c
• • Copyright (C) 2013 Linaro Limited
• • Author: AKASHI Takahiro takahiro.akashi@linaro.org
• • This program is free software; you can redistribute it and/or modify
• • it under the terms of the GNU General Public License version 2 as
• • published by the Free Software Foundation.
• */

+#include <linux/export.h> +#include <linux/ftrace.h>

+#include <asm/stacktrace.h>

+struct return_address_data {

• unsigned int level;
• void *addr;

+};

+static int save_return_addr(struct stackframe *frame, void *d) +{

• struct return_address_data *data = d;
• if (!data->level) {

• data->addr = (void *)frame->pc;
  

• return 1;
  

• } else {

• --data->level;
  

• return 0;
  

• }

+}

+void *return_address(unsigned int level) +{

• struct return_address_data data;
• struct stackframe frame;
• register unsigned long current_sp asm ("sp");
• data.level = level + 2;
• data.addr = NULL;
• frame.fp = (unsigned long)__builtin_frame_address(0);
• frame.sp = current_sp;
• frame.pc = (unsigned long)return_address; /* dummy */
• walk_stackframe(&frame, save_return_addr, &data);
• if (!data.level)

• return data.addr;
  

• else

• return NULL;
  

+} +EXPORT_SYMBOL_GPL(return_address);

This whole file is basically copied from arch/arm/, but it's not too much code. Ideally the toolchain would have made use of the frame pointer, but it looks like it doesn't bother.

Will