On Fri, Jun 26, 2020 at 09:30:14PM +0300, Dmitry Shachnev wrote:
> Some more information on this: it looks like dlopen'ing libGLX_mesa.so.0
> returns NULL (src/GLX/libglxmapping.c:430).
>
> LD_PRELOAD'ing that library helps. Adding the following two lines to top
> of web_engine_initialize.py also helps:
>
> import ctypes
> ctypes.CDLL('libGLX_mesa.so.0', ctypes.RTLD_GLOBAL)
>
> I can't say why dlopen fails without that, though.
Some more information on this. I remembered that there is dlerror function,
and checked its output:
$ gdb python3
(gdb) r ./test.py
[...]
(gdb) b libglxmapping.c:432
Breakpoint 1 at 0xfffff54f5f08: file ../src/GLX/libglxmapping.c, line 432.
(gdb) r
[...]
Thread 1 "python3" hit Breakpoint 1, __glXLookupVendorByName (vendorName=<optimized out>) at ../src/GLX/libglxmapping.c:432
(gdb) p vendor->dlhandle
$1 = (void *) 0x0
(gdb) p (char *)dlerror()
$2 = 0xc54f60 "/usr/lib/aarch64-linux-gnu/libglapi.so.0: cannot allocate memory in static TLS block"
So this is the real reason for this failure.
I have searched the internet and found a couple of bug reports with a similar
problem:
- https://github.com/opencv/opencv/issues/14884
- https://bugzilla.redhat.com/show_bug.cgi?id=1722181
The last link mentions a glibc patch from ARM that is currently under review:
https://sourceware.org/pipermail/libc-alpha/2020-May/114247.html
Unfortunately my knowledge of library loading process is little. I am CCing
glibc and mesa maintainers: maybe they can tell more about this issue?
Finally, a very short Python reproducer for this bug (needs libqt5webengine5):
#!/usr/bin/python3
import ctypes
ctypes.CDLL("libQt5WebEngine.so.5")
ctypes.CDLL("libglapi.so.0")
fails with:
Traceback (most recent call last):
File "./test.py", line 4, in <module>
ctypes.CDLL("libglapi.so.0")
File "/usr/lib/python3.8/ctypes/__init__.py", line 373, in __init__
self._handle = _dlopen(self._name, mode)
OSError: /usr/lib/aarch64-linux-gnu/libglapi.so.0: cannot allocate memory in static TLS block
--
Dmitry Shachnev
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