bugAVR C Runtime Library - Bugs: bug #52181, assert should make Serial.flush()...


bug #52181: assert should make Serial.flush() before calling abort()

Submitted by:  Hannes Studeny <pukuri>
Submitted on:  Sat 07 Oct 2017 02:58:08 AM UTC  
Category: LibrarySeverity: 3 - Normal
Priority: 5 - NormalItem Group: libc code
Status: Wont FixPercent Complete: 0%
Assigned to: NoneOpen/Closed: Closed
Release: AnyFixed Release: None

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Sun 08 Oct 2017 06:59:36 PM UTC, comment #3:

Thanks a lot for your help and pointing me in the right direction!

Added a Destructor to the Serial class, temporarily enabled the interrupts, to print out the last bytes, freed some resources and it worked like a charm.

Sadly it showed me again how buggy the Arduino environment is...

Hannes Studeny <pukuri>
Sun 08 Oct 2017 05:47:12 PM UTC, comment #2:

I agree with Johann on that. There's nothing avr-libc could do about it.

If Arduino (which I think is what you are talking about) needs
a Serial.flush() before disabling interrupts, I think it would
be best if the Arduino environment would override abort() by
their own implementation. While this is not really covered by
the C standard (library functions must not be reimplemented by
the application), I think it will work well here. If not, we
could always resort to implementing an overridable _Abort()
backend function that can then be reimplemented by the Arduino

Joerg Wunsch <joerg_wunsch>
Project Administrator
Sun 08 Oct 2017 09:34:46 AM UTC, comment #1:

This is not an avr-libc problem. The stdio routines like prinf are fully synchronous, and there is no buffering.

Hence any buffering must emerge from the applicaton's stream implementation, i.e. from the callbacks you are providing with FDEV_SETUP_STREAM or by similar means.

One fix is to provide a destructor for your static buffering object. abort will call _exit which will run all the static destructors and all the functions registered with atexit.

Beside thar, gnu tools allow to provide own static destructors even for C, and avr tool allow to override abort, _exit and exit and to run own shutdown code located in dedicated sections .fini9 ... .fini0.

Georg-Johann Lay <gjlayde>
Sat 07 Oct 2017 02:58:08 AM UTC, original submission:

I'm quite new to this project, hopefully I'm submitting this bug at the corect place, if not, please point me in the right direction...

if the expression in the assert function fails, a fprintf to stderr is made and then the function abort() is called which runs in an endless loop.

The problem is, because the abort() function disables all interrupts (which is fine), the remaining bytes in the buffer for the serial interface will not be printed (not so good). Only the very first couple of bytes will be seen.

recomended solution: just before calling abort think about calling Serial.flush(), or similar...

Problem with this solution is, that Serial.flush comes from the Arduino environment and has nothing to do with libc, but on the other hand fflush() does nothing

So, I have no real solution for this problem, but hopefully the insiders might come up with something.

Right now the assert function is useless, because one get no information where and why the program stops.

Hannes Studeny <pukuri>


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    Follow 2 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Sun 08 Oct 2017 05:47:12 PM UTCjoerg_wunschStatusNone=>Wont Fix

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