Re: [patch V2 28/29] stacktrace: Provide common infrastructure

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Thu, Apr 18, 2019 at 10:41:47AM +0200, Thomas Gleixner wrote:
> All architectures which support stacktrace carry duplicated code and
> do the stack storage and filtering at the architecture side.
> 
> Provide a consolidated interface with a callback function for consuming the
> stack entries provided by the architecture specific stack walker. This
> removes lots of duplicated code and allows to implement better filtering
> than 'skip number of entries' in the future without touching any
> architecture specific code.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: linux-arch@vger.kernel.org

This is a step in the right direction, especially if it allows us to get
rid of the 'skip' stuff.  But I'm not crazy about the callbacks.

Another idea I had (but never got a chance to work on) was to extend the
x86 unwind interface to all arches.  So instead of the callbacks, each
arch would implement something like this API:


struct unwind_state state;

void unwind_start(struct unwind_state *state, struct task_struct *task,
		  struct pt_regs *regs, unsigned long *first_frame);

bool unwind_next_frame(struct unwind_state *state);

inline bool unwind_done(struct unwind_state *state);


Not only would it avoid the callbacks (which is a nice benefit already),
it would also allow the interfaces to be used outside of the
stack_trace_*() interfaces.  That would come in handy in cases like the
ftrace stack tracer code, which needs more than the stack_trace_*() API
can give.

Of course, this may be more work than what you thought you signed up for
;-)

-- 
Josh