That's got to be the worst kind of bug - I know it's been fixed but I
can't remember what fix it was (assuming it was me who fixed it).
Without a reproducible case I can't exactly identify the patch that
fixes it, and yet I don't want to leave FPC 3.2.0 in a state where the
optimizer is in an unreliable state.
Gareth aka. Kit
On 10/07/2021 13:53, Martin Frb via fpc-devel wrote:
On 10/07/2021 06:40, J. Gareth Moreton via fpc-devel wrote:
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.
-------------------------------------
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...
-----
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....
--------------------------
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)
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