Re: [PATCH 1/3] gdb: Added builtin types for 24 bit integers.

[John Darrington <john@darrington.wattle.id.au>]

On Thu, Aug 23, 2018 at 04:35:25PM -0400, Simon Marchi wrote:

     It is clear now, but somebody doing a git blame to know why 24-bit
     integer types were added would only find the patch that adds them by
     itself and wonder who uses that.  A little message like
     
       This patch adds 24-bit integer types, used when debugging on the S12Z
     architecture (added by a later patch in this series).
     
     clears that up.  That might looks a bit silly, but I think it helps in
     the long run.

I fully agree with you.   I've worked on other projects however had a
different opinion - they insisted that the checkin comment NOT contain
any rationale for the change, instead it should just summarize what
changed.  I find that rather pointless but anyway ....
     
     > It seems that up till now there has been no 24 bit targets, so the
     > other
     > two patches as some necessary things to make that possible.
     
     Thanks.  Coming back to the code of the patch, I was wondering if these
     24-bit types are useful or even relevant for any other architecture.

There most certainly are plenty of 24 bit architectures  especially in the 
embedded world  - just apparently none that gdb currently supports :(

     Would it work if you only defined the types for s12z architectures,
     storing the reference in the gdbarch_tdep object?

My first reaction is that it probably *could* be made to work, but not 
in an elegant fashion.   Somehow I'd have to avoid that gdb ever calls the 
read_encoded_value function. 

I do concede that  adding DW_EH_PE_udata3 might be problematic since
it's not part of the dwarf standard.  An alternative might be to rework
the read_encoded_value function to not rely on the dwarf enums (all it
really cares about is the size of the target's address space.

Regards

John




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