Re: cortex-m xml register descriptions for m-system

[Tristan Gingold <gingold@adacore.com>]

> On 16 Dec 2015, at 18:12, Christopher Friedt <chrisfriedt@gmail.com> wrote:
> 
> On Wed, Dec 16, 2015 at 8:51 AM, Tristan Gingold <gingold@adacore.com> wrote:
>> 
>>> On 15 Dec 2015, at 16:35, Christopher Friedt <chrisfriedt@gmail.com> wrote:
>>> 
>>> Just so we can have consensus, please indicate what you think is the
>>> best solution - Pedro, Yao, & Tristan.
>>> 
>>> Based on Tristan's feedback as well, it confirms that these registers
>>> are necessary for DWARF handling.
>> 
>> Not sure about that.  To my understanding, DWARF doesn’t need to refer
>> to psp or msp.
> 
> Wait... just yesterday you wrote:
> 
> "I do think so too.
> 
> I have just written a patch so that gdb unwinds correctly on cortex-m
> exceptions, and this of course requires that gdb knows about at least
> psp."
> 
> Maybe I'm confused. I presumed DWARF was involved in unwinding to some
> extent, but if its purely just used for debugging, it might not
> require PSP / MSP at all.

No, for unwinding through HW exceptions, dwarf is not used and couldn’t
be use: there is no code at the return addresses.

PSP is required because that can be previous stack before the exception.

> In any case PSP / MSP are most definitely used in unwinding.

I think that only PSP and SP are required (of course SP could be MSP).

Tristan.