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Re: [avr-gcc-list] using exceptions

From: Don Kinzer
Subject: Re: [avr-gcc-list] using exceptions
Date: Tue, 1 May 2012 11:49:24 -0700

> Gabriel Dos Reis wrote:
>I guess I would need to get my feet wet with
>   1. minimal free-standing  C++ implementations without exceptions
As for getting started, you'll find much of the collected knowledge
about using C++ on AVRs in the AVR Freaks thread below.

There are some other issues that are not in that thread.  For example,
the long-used method for applications to define data residing in Flash
(prog_char typedef, et al) causes warnings in C++ with newer compiler
versions (circa avr-gcc 4.2.2 and later).  See the AVR Freaks thread
for more information.  I haven't looked into how (or, in fact, if) the
Arduino environment resolves this issue.

> Gabriel Dos Reis wrote:
>   2. get support for RTTI (without exceptions)
>RTTI data are generally const and should be best stored in read only location.
The same is true for v-tbl information, too.  However, in the current
implementation the v-tbl is in RAM (initialized with data from Flash).
 See the AVR Freaks thread below for some discussion.

>   3. exceptions (assuming 1 and 2 are done successfully)
I would guess that implementing unwinding would require frame pointers
for all of the functions in the call hierarchy.  Currently, frame
pointers are turned off (-fomit-frame-pointer) with any optimization
above -O0 (I think).  This aspect of optimization would need to change
for applications built with exception handling.  A special version of
avr-libc, built to support exception handling, may be required, too.
This is all speculation on my part and may or may not be useful.

Don Kinzer

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