[boost] libstdc++ debug mode

Subject: [boost] libstdc++ debug mode
From: Robert Ramey (ramey_at_[hidden])
Date: 2016-10-30 18:16:33

Back on May 2 2016 I made what I thought was an innocuous change to the 
serialization library build.

I then forgot about it.  I ran my tests and normal on my OSX set up for 
the compilers that I use there - clang and g++ 5.1 in various modes 03, 
11 etc.  Things seemed fine.  I uploaded the develop branch as normal. 
Sometime later I discovered that all the gcc tests on linux platforms 
were failing with a segfault.  Unfortunately time had passed and I 
couldn't run the tests myself so I never could figure out what the 
breaking change was.

Lately I separated time to get to the bottom of this and in installed 
via Parallels ubuntu v 14 on my Mac as a guest operating system.  After 
the usual back and forth getting stuff to work I was able to reproduce 
the problem.  Running gdb indicated that things crashed with a call to 
boost::io::state_saver which led me to investigate THAT library which as 
it turned out is also failing all it's tests on the plaform.  So thought 
I - no problem - all I have to do is to complain to the author of that 
library.  But this didnt' workout

a) I posted message and no one responded.

b) I checked trac items and there was what seemed a related item.  But 
it seemed a little hard to understand/fix and in any case, no one 
addressing it.  I looked into just fixing it myself, but it looked to 
entail delving into the bowels of libstd++.  So this dissuaded me as I 
have my own bowels to delve into.

c) So I commented out references to boost::io::state_saver an ran some 
tests - and damn still failed.

d) So I rolled back my source to the master dated 24 April 2016 and 
incrementally updated and ran some tests until I found the culprit.

Needless to say, this is quite a tedious procedure.  The issue seems to 
be that I added the following to the jamfile:

<toolset>gcc:<define>_STLP_DEBUG
<toolset>gcc:<define>_GLIBCXX_DEBUG

The second adds a lot of checking. commenting this permitted tests to 
pass.  Lesson of all this is:

a) I'm thinking we should run all tests on the deelop branch with 
_GLIBCXX_DEBUG defined. That is, our jam files should contain?:

<toolset>gcc:<variant>debug><define>_GLIBCXX_DEBUG

b) it looks like when an error in libstd++ is encounted - things just 
segfault.  I couldn't find the corresponding source in libstd++.  GDB 
just bailed when I made a call to state_saver.

c) boost::io::state_saver should be maintained.

d) It would be helpful to be able to roll back the test matrix to any 
previous git version.  That is, the results would be put into a database 
or datacube and we could scroll back and forth to see track down 
problems in test results.

Robert Ramey