linux-kernel - Re: [PATCH 19/19] [INCOMPLETE] ARM: make return_address available for ARM

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Date:	Tue, 07 Jan 2014 16:48:25 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	linux-arm-kernel@...ts.infradead.org,
	sahara <keun-o.park@...driver.com>,
	Keun-O Park <kpark3469@...il.com>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Dave Martin <Dave.Martin@....com>
Subject: Re: [PATCH 19/19] [INCOMPLETE] ARM: make return_address available for ARM_UNWIND

On Tuesday 07 January 2014 14:41:30 Russell King - ARM Linux wrote:
> On Tue, Jan 07, 2014 at 03:33:34PM +0100, Arnd Bergmann wrote:
> > 
> > 
> > It's been almost a year since we last discussed the patches that were
> > posted by Dave and sahara, but nothing has changed in the mainline kernel.
> > 
> > Any chance that someone could be motivated to pick this work up again
> > and finally fix return_address().
> 
> I thought that we had _actively_ decided that we would not use the
> unwinder for these paths - that it was too expensive for these paths,
> and you had to use frame pointers instead.

I don't remember that discussion, but it may well be. What does
that mean for the #warning in return_address.c then? Can we
just use the frame pointer version based on CONFIG_FRAME_POINTER
and ignore whether CONFIG_ARM_UNWIND is set as the patch below,
or did I misunderstand?

	Arnd

diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index f89515a..3247370 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -32,7 +32,7 @@ extern void ftrace_call_old(void);
 
 #ifndef __ASSEMBLY__
 
-#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
+#if defined(CONFIG_FRAME_POINTER)
 /*
  * return_address uses walk_stackframe to do it's work.  If both
  * CONFIG_FRAME_POINTER=y and CONFIG_ARM_UNWIND=y walk_stackframe uses unwind
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index a30fc9b..c713f46 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -16,13 +16,14 @@ CFLAGS_REMOVE_return_address.o = -pg
 # Object file lists.
 
 obj-y		:= elf.o entry-common.o irq.o opcodes.o \
-		   process.o ptrace.o return_address.o \
+		   process.o ptrace.o \
 		   setup.o signal.o sigreturn_codes.o \
 		   stacktrace.o sys_arm.o time.o traps.o
 
 obj-$(CONFIG_ATAGS)		+= atags_parse.o
 obj-$(CONFIG_ATAGS_PROC)	+= atags_proc.o
 obj-$(CONFIG_DEPRECATED_PARAM_STRUCT) += atags_compat.o
+obj-$(CONFIG_FRAME_POINTER)	+= return_address.o
 
 ifeq ($(CONFIG_CPU_V7M),y)
 obj-y		+= entry-v7m.o v7m.o
diff --git a/arch/arm/kernel/return_address.c b/arch/arm/kernel/return_address.c
index fafedd8..d9f2c15 100644
--- a/arch/arm/kernel/return_address.c
+++ b/arch/arm/kernel/return_address.c
@@ -10,8 +10,6 @@
  */
 #include <linux/export.h>
 #include <linux/ftrace.h>
-
-#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
 #include <linux/sched.h>
 
 #include <asm/stacktrace.h>
@@ -56,18 +54,4 @@ void *return_address(unsigned int level)
 	else
 		return NULL;
 }
-
-#else /* if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND) */
-
-#if defined(CONFIG_ARM_UNWIND)
-#warning "TODO: return_address should use unwind tables"
-#endif
-
-void *return_address(unsigned int level)
-{
-	return NULL;
-}
-
-#endif /* if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND) / else */
-
 EXPORT_SYMBOL_GPL(return_address);

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