Re: [sdcc-devel] SDCC stm8 debug info

[Åke R. <ake...@gm...>]

On 2017-05-10 23:18, Philipp Klaus Krause wrote:
> Am 10.05.2017 um 23:00 schrieb Åke Rehnman:
>> On 2017-05-10 22:55, Philipp Klaus Krause wrote:
>>> But stm8 codegen basically does all stack-pointer-changing stuff in the
>>> three functions push(), pop() and adjustStack(). Does that help in any way?
>>>
>>> The stm8 codegen also supports the use of a frame-pointer, which
>>> currently is rarely used. If it is useful for debugging, I could however
>>> easily implement --fno-omit-frame-pointer for stm8.

If we can get CFA working fp is not required or even desirable.

> Line 356 in src/stm8/gen.c handles the variable access using the frame
> pointer. Line 3050 does the frame pointer setup. However, the caller is
> responsible for saving and restoring the frame pointer, so it might be
> unavailable for a short while after a function call.

> Support for the frame pointer has been in there for a long time: The
> offsets for sp-relative addressing on the STM8 are 8-bit only, while we
> can use 16-bit offsets on the register y, which is used as a frame
> pointer. We thus use the frame pointer when there is so much stack space
> used by local variables that we can't use sp-relative addressing for all
> them.
Ok, *that* I've seen. Well I was not sure if the Y register would be 
available at all times (except during prologue). Also the requirement 
for frame unwinding to work in gdb is the prologue is consistent and 
possible to disassemble in a reliable way. Anyhow it was quick patch 
just a few lines of code to get a soft fp.

/Ake