Messages in this thread | | | Subject | Re: [RFC] microblaze: Support FRAME_POINTER for better backtrace | From | "Steven J. Magnani" <> | Date | Wed, 10 Mar 2010 16:51:16 -0600 |
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I've had some time to bake a Microblaze implementation of this and have come up with a question...
On Mon, 2010-03-01 at 15:26 -0600, Steven J. Magnani wrote: > On Mon, 2010-03-01 at 10:43 +0900, Paul Mundt wrote: > > This doesn't look that bad compared to what some of the other > > architectures have to deal with. If the frame pointer is always setup > > using these addik/swi pairs then you can trivially scan an arbitrary > > number of instructions attempting to match before giving up. We do > > similar things for sh64 where we also have to figure out how stack frames > > were created in order to roll them back. > > > > In any event, take a look at arch/sh/kernel/cpu/sh5/unwind.c, you should > > be able to use a similar scheme without the need for undue complexity. > > > > Thanks for the tip. This looks manageable. I had thought to search for > instructions that create frames but didn't think working backwards from > return addresses was a good idea. Using kallsyms to get the "top" of > each function is a nice way around that.
The kallsyms approach to unwinding depends on as many functions as possible being in the table, for two reasons:
* The unwind can't get past an address that kallsyms can't identify * A mis-lookup, such as reporting a nearby global function when the actual address lies in a static function, can send the unwind off the rails
To get static (local) functions into kallsyms, I've found that I need to specify -fno-unit-at-a-time to Microblaze gcc 4.1.2. I suspect that particular option has other side-effects, but despite much searching I couldn't find any mention of a gcc option that would do what I need. My x86_64 gcc (4.4.1) seems to emit local symbols by default even with -funit-at-a-time.
Any suggestions?
------------------------------------------------------------------------ Steven J. Magnani "I claim this network for MARS! www.digidescorp.com Earthling, return my space modulator!"
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