[sdcc-devel] [ sdcc-Bugs-3600983 ] Endless loop in modulong.c

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Bugs item #3600983, was opened at 2013-01-15 07:28
Message generated for change (Comment added) made by mbtronics
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Category: pic16 target
Group: non bugs
Status: Closed
Resolution: Fixed
Priority: 5
Private: No
Submitted By: Maarten Blomme (mbtronics)
Assigned to: Raphael Neider (tecodev)
Summary: Endless loop in modulong.c

Initial Comment:
I am working on a large piece of code for a 18F2550. I have had it several times that the watchdog went off.
I was able to trace the problem to an endless loop in _modulong. I think this is the code in lib/pic16/libsdcc/long/modulong.c. The code for the pic14 target has an extra line with comments ("/* prevent endless loop (division by zero exception?!?) */") which the pic16 code does not have. Could this be the problem?

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Comment By: Maarten Blomme (mbtronics)
Date: 2013-01-15 23:45

Message:
I did some more debugging, and the original function call is a printf, but
I don't know exactly with which parameters.
If _modulong may not be called with b==0, there may be a problem somewhere
between printf and _modulong.

The problem is that I have a hard time reproducing this. My code prints the
temperature every half second to the serial port, but the endless loop
seems to happen at random. Sometimes it takes 9 hours, sometimes 1 hour.

printf("Temp: %d\n\r", temperature);


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Comment By: Raphael Neider (tecodev)
Date: 2013-01-15 14:55

Message:
I "fixed" _modulong(a, b) to return ~0UL for b==0 instead of entering an
infinite loop in r8388.

However, if your program triggered this division-by-0 several times
already, you may have to look into your code again: Division-by-0 triggers
undefined behaviour as per the C standard (see, e.g., Clause 6.5.5.5 in
draft N1548), so that an endless loop is a perfectly valid implementation.

Raphael

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