On Thu, 2014-03-13 at 15:54 +0000, Will Deacon wrote:
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?
Perhaps -pg does the same thing?
+#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?
We could add a new macro:
/* All archs should have this, but we define it for consistency */ #ifndef ftrace_return_address0 # define ftrace_return_address0 __builtin_return_address(0) #endif /* Archs may use other ways for ADDR1 and beyond */ #ifndef ftrace_return_address # define ftrace_return_address(n) __builtin_return_address(n) #endif
And then have:
#define CALLER_ADDR0 ((unsigned long)ftrace_return_address0) #define CALLER_ADDR1 ((unsigned long)ftrace_return_address(1)) [...]
And then you would only need to redefine ftrace_return_address.
-- Steve