Cygwin trouble: lyx 1.3.3 builds but crashes.

[Sivan Toledo]

I am trying to build lyx 1.3.3 with a qt frontend on cygwin. I got to 
the point that qt and lyx both build successfully (no changes to the lyx 
sources, and almost none to qt-x11). Qt runs the examples, but lyx dies 
before it opens the first window. It says it crashed with a segmentation 
fault and asks to report the bug.

Here are the details:

I built qt-x11 with gcc-2.95.3-10 (cygwin special); I couldn't get it to 
compile with gcc 3. I did this by using the cygwin mkspec, but changing 
to gcc-2 and g++2, by telling it not to use DNS, and not to build the 
network module. I also forced the OS and WS to UNIX and X11, because qt 
discovers (using a gcc macro) that it is on cygwin and tries to do a 
windows build, which fails because you can't do it in the GPL version. 
So this works, the examples run well. This is a static qt, not a dll. I 
couldn't build the dll.

Next LyX. I was able to compile it and link with g++-2. I had to force 
it not to use -fnative-struct, otherwise the program crashed on the 
first call to Qt (to get the screen DPI). I also used -fno-exceptions, 
like Qt. This program runs for a short bit but crashes. When I used 
strace, I found that it crashed because it was trying to do mmap2 on 
about a gigabyte (anonymous), right after opening and calling fstat() on 
banner.ppm. A little more searching found that the problem was coming 
from the C++ std library, which tries to use MMAP for the file buffer on 
rdbuf on a file stream. On linux it allocates small buffers and 
continues, on cygwin it tries to allocate a huge buffer and dies.

I tried to build a new version of the C++ std library without MMAP, but 
was not able to build thd gcc2 binaries and libraries properly. The 
version I have came from the KDE-CYGWIN project.

I find it hard to believe that the problem is a bug in the stream IO 
library of g++ 2.95.3, so I think that the problem is probably some 
memory overwriting. Perhaps it is caused by some linking problem (like 
native-structs vs non-native structs), and perhaps from a bug in lyx. I 
tried lyx 1.3.2 and the same problem appeared.

I think that I am pretty close to getting this to work with versions of 
qt and lyx that are not hacked at all, but I really got stuck with this 
problem. If somebody has any idea, please let me know (and please cc me 
on the email).

Regards, Sivan Toledo