[ruby-talk:12542] Re: Strange segmentation fault problem with C++ extension

I know it is probably bad form to reply to oneself however I just wanted to
apologise for the awful grammar/spelling of this message. Of course, the
errors only revealed themselves after the message has been posted and I was
reading through the version sent out to the world !

Regards, Paul


"Paul C" <[e-mail]> wrote in message
news:[e-mail]...
> Hi,
>
> I have been beating my head against the monitor for a couple of days with
a
> repeatable segmentation problem with a C++ extension - I am sure that
there
> is something obvious that I am missing and would be grateful for any
advice.
>
> I am trying to create a Ruby wrapper for the ZIPIOS C++ Zip file reader
> library (http://zipios.sourceforge.net). I managed to get this mostly
> working however I have been stuck with a deterministic problem with the
> extension core dumping in the method to extract a zip file entry under the
> following conditions -
>
> - Running under IRB
>
> - Calling the method without a 'begin/rescue' block (ie caught
interactively
> by IRB)
>
> - (Optional) Call the method with a filename which exists in archive -> OK
>
> - Call the method with a filename which does not exist in the archive ->
> Throws an exception
>
> - Call the method with a filename which does exist -> Core Dump
>
> If the failing method call is enclosed in a begin/rescue block the problem
> goes away (which would always be the case outside the interactive shell).
>
> If the method is called multiple times with a valid entry or even multiple
> times with an invalid entry it works fine - it is just the sequence
> invalid/valid which causes the program to crash.
>
> Unfortunately I am not a C++ programmer (and following this experience
have
> no desire to become one) so I would ask you to excuse the code - however I
> wasnt able to find a C Zip file library. I am concerned that there is an
> underlying problem in the code somewhere which is causing this but havent
> been able to make any progress (I will of course be releasing the module
to
> the RAA once I get this fixed).
>
> I have instrumented the module and the strange thing is that there is no
> apparent difference in the calling sequence between a method that succeeds
> and a subsequent method that causes a segmentation fault (after an
> intervening request for an non-existant entry).
>
> The source code for the method that is failing is at the end of the
> message - if anyone would like the source code to the whole extension
please
> let me know and I will e-mail it.
>
> The debug trace below is equivalent for the first/third calls (which
should
> be the same without the failing call between them). The final debug print
of
> the return VALUE is generated immediately before the method returns and
> shows the the VALUE to be returned has been created successfully within
the
> method. The method segemntation faults when the functio tries to return
the
> VALUE.
>
> I am at a loss as to why this happens - any suggestions ?
>
> Regards, Paul
>
> PS. I forgot the obligatory thanks to Matz and the Ruby community for a
> great language - it is a pleasure to use (and hopefully extend if I can
get
> this !#$&&*# module working!)
>
> PPS. Versions are - Ruby 1.6.3 / NetBSD 1.5
>
> =========== DEBUG TRACE ===========
>
> # irb --prompt xmp
>
> require 'Zip'
>     ==>true
>
> z = Zip::ZipFile.new "test.zip"
>     ==>#<Zip::ZipFile:0x816c424 @name="test.zip">
>
> z.entries { |e| print e.path, "\n" }   # Get Zip Directory
> extconf.rb
> Makefile
>     ==>#<Zip::ZipFile:0x816c424 @name="test.zip">
>
> z.entry "extconf.rb"                   # OK
>     (zip.cpp:186) MSG: Entering Function #ZipFile_entry
>     (zip.cpp:187) VALUE: self -> #<Zip::ZipFile:0x816c424
@name="test.zip">
>     (zip.cpp:191) PTR: ZipFile ->135501760
>     (zip.cpp:201) MSG: GetEntry OK
>     (zip.cpp:203) PTR: ConstEntryPointer ->135870784
>     (zip.cpp:205) VALUE: zipLocalEntry -> #<Zip::ZipEntry:0x81545cc
> @path="extconf.rb">
>     ==>#<Zip::ZipEntry:0x81545cc @path="extconf.rb">
>
> z.entry "zzzzzzz"                      # Invalid Entry
>     (zip.cpp:186) MSG: Entering Function #ZipFile_entry
>     (zip.cpp:187) VALUE: self -> #<Zip::ZipFile:0x816c424
@name="test.zip">
>     (zip.cpp:191) PTR: ZipFile ->135501760
>     (zip.cpp:196) MSG: GetEntry Failed
> RuntimeError: Entry not found
> (irb):10:in `entry'
> (irb):10:in `irb_binding'
>
> z.entry "extconf.rb"                   # Should be OK
>     (zip.cpp:186) MSG: Entering Function #ZipFile_entry
>     (zip.cpp:187) VALUE: self -> #<Zip::ZipFile:0x816c424
@name="test.zip">
>     (zip.cpp:191) PTR: ZipFile ->135501760
>     (zip.cpp:201) MSG: GetEntry OK
>     (zip.cpp:203) PTR: ConstEntryPointer ->136008256
>     (zip.cpp:205) VALUE: zipLocalEntry -> #<Zip::ZipEntry:0x814d36c
> @path="extconf.rb">
> (irb):12: [BUG] Segmentation fault
> ruby 1.6.3 (2001-03-07) [i386-netbsd1.5]
> Abort (core dumped)
>
> =========== METHOD SOURCE ===========
>
> static VALUE ZipFile_entry ( VALUE self, VALUE name ) {
>
>     VALUE zipLocalEntry = Qnil ;
>     ConstEntryPointer entry ;
>     ConstEntryPointer *ptr_entry ;
>     ZipFile *zf ;
>
>     const string sname = STR2CSTR(name) ;
>
>     DEBUG_MSG("Entering Function #ZipFile_entry") ;
>     DEBUG_VALUE("self",self) ;
>
>     Get_ZipFile ( self, zf ) ;
>
>     DEBUG_PTR("ZipFile",zf) ;
>
>     try {
>         if ( (entry = zf->getEntry(sname)) == 0 ) {
>
>             DEBUG_MSG("GetEntry Failed") ;
>             rb_raise ( rb_eRuntimeError, "Entry not found" ) ;
>         }
>         else {
>
>             DEBUG_MSG("GetEntry OK") ;
>             ptr_entry = new ConstEntryPointer ( entry ) ;
>             DEBUG_PTR("ConstEntryPointer",ptr_entry) ;
>             zipLocalEntry = ZipLocalEntry_new ( ptr_entry ) ;
>             DEBUG_VALUE("zipLocalEntry",zipLocalEntry) ;
>
>             return zipLocalEntry ;
>         }
>     }
>     catch ( exception &excp ) {
>
>         DEBUG_MSG("Exception") ;
>         rb_raise ( rb_eRuntimeError, excp.what() ) ;
>     }
> }
>
>
>
>
>
>