qt5XX-qtwebkit dependency on leveldb causes crashes

[Veence (Vincent)]

qtwebkit depends on leveldb, which in turn depends on gperftools.

One, or both, of those dependencies seems buggy. Qgis3, which links against qtwebkit, keeps crashing in various dialogs (with messages like [src/tcmalloc.cpp]: attempt to free unknown pointer at {some address}).

Remove qtwebkit’s dependency on leveldb and not only it keeps on building fine, but the bugs are gone. So that dependency seems to be toxic. Why does it exist, given that qtwebkit seems to compile fine without?

Thanks

[MarcusCalhoun-Lopez (Marcus Calhoun-Lopez)]

qtwebkit ​tests to see if there is a system version of leveldb by trying to ​compile a program.
If no system leveldb is found, qtwebkit ​builds its own.

I am not sure why the system version would cause these problems.
Any help narrowing down this problem would be appreciated.

[Veence (Vincent)]

I have at that point no clue as to the culprit. It seemed to me that the current version of qtwebkit, when compiled with an external leveldb, reports using both the internal and third party code, but that might be misinterpreting something. I’ll try again this morning and let you know.

Other hypothesis: “gperftools” is buggy and Qt-internal leveldb doesn’t use it. Is there a way to compile leveldb without using gperftool’s tcmalloc library?

Other possibility: “gperftools”, if used internally by Qt, is compiled with less stringent behavorial rules and does not abort on freeing wrong addresses (which may give rise to leaks, but otherwise don’t plague the application behavior).

I’d have to look into this, but that entails recompling all those ports with “-g -O0” flags and using XCode/LLDB/Instruments to monitor the defects. It’s not unfeasable, but there may be simplier way to address this rather than going the whole hog.

[Veence (Vincent)]

Ok, using leveldb without the gperftool dependency works. So it’s definitely gperftool which causes the whole shebang to run amok.

[MarcusCalhoun-Lopez (Marcus Calhoun-Lopez)]

This discussion seems to have moved back to #56164.
There is a potential fix in leveldb.

[ryandesign (Ryan Carsten Schmidt)]

Just removing the gperftool dependency can't possibly fix the problem for users who build from source. The build system must also be informed not to use gperftool even if it is already installed.

[Veence (Vincent)]

Should be fix in commit 8a10bcb2c08195cc926b81e78e0ac6967985688c. ​https://github.com/macports/macports-ports/commit/8a10bcb2c08195cc926b81e78e0ac6967985688c