J. Gareth Moreton wrote 9 lines
Hi everyone,
So I want to fix that optimisation bug in FPC 3.0.2 and 3.2.0 etc, but
I need a little bit of help. I know that Lazarus doesn't build
properly with optimisations, but does anyone know of a smaller project
that compiles incorrectly and causes an easy crash when run? If not,
what do I need to do with Lazarus to make it crash? With that, I can
do a kind of manual binary search with revisions to find the point
where it no longer crashes (since it was fixed for FPC 3.3.1).
The one that I got is very hard to catch.
It seem to me, that something is doing a write to random memory. So any tiny change, and the bug disappears.
This is the revision that for me reproduces it.
https://github.com/User4martin/lazarus/tree/f-fpc-crash-fpdebug
The testcase is
components\lazdebuggers\lazdebuggerfp\test\LazDebFpTest.lpi build mode "64bit -O2"
To run it you need to copy fpclist.txt.sample to fpclist.txt edit it, and point it to your fpc (can be an older, can be trunk, does not have to be the crashing version)
you need only one fpc in it.
You also need to create some folders
logs/
lib/
testapps/lib/
And it is Windows 64 bit only.
Make sure it crashes for you, before trying to hunt down what it is.
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I tried to create a console test case => but then it does not crash.
If you use OoNOPEEPHOLE => no crash
If you use "implicit exception off" => no crash
see https://github.com/User4martin/lazarus/tree/f-fpdebug-fpc-optimizer-bug
I did trace it down to the specialization of some generic, that needed to be done while "implicit exception off"
But that is a lot of functions...
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All that said, I know there is no proof the bug is not in my code. It's just based on likelyhood.
I valgrinded the crap out of it. Nothing.
Well it is only windows, but if I accessed a dangling pointer, valgrind would find it, even if it caused no harm on Linux. So the bug is apparently not in the compiled code on Linux.
And that is basically all I have....
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you can edit the project file and change
TestRunner.RunExecute(TestRunner);
//Application.Run;
then the test runs automatically.
Or even
TestRunner.Show;
TestRunner.RunTest(TTest(TestRunner.TestTree.Items[0].Items[2].Data));
To run just a small subset of tests (you might need to change that depending on your fpclist.txt)
