Thanks Jonas, that confirms what I suspected. Next time I trap an instance of this (rare) fault I will inspect exactly which CPU instruction raised the SEGV inside fpc_AnsiStr_Decr_Ref in search of a source of memory corruption.
Bruce. On Wed, May 8, 2013 at 11:49 PM, Jonas Maebe <jonas.ma...@elis.ugent.be>wrote: > > On 08 May 2013, at 08:13, Bruce Tulloch wrote: > > After a random but very long period of time (i.e. very many successful >> calls) I get a SEGV in the built-in function fpc_AnsiStr_Decr_Ref. >> >> GDB reports the argument to fpc_AnsiStr_Decr_Ref (the string who's >> reference is to be decremented) is nil (i.e. 0x0). >> >> Prima facie, that's the reason for the SEGV, but how is it possible that >> the compiler would pass a nil pointer to this function the first place? >> > > The first thing fpc_AnsiStr_Decr_Ref does is check whether its parameter > is nil, and if so it immediately exists. It can be nil in case the > ansistring contains an empty string. > > That routine itself also sets its argument to nil in case this was not the > case initially (it's a var-parameter), and I assume your crash happens > after this has been done. > > > To put this into context, I'm running FPC 2.6.2 on a 32 bit Linux system >> executing in a multi-threaded application (which uses python threads and >> fpc threads). I have not found obvious evidence of memory corruption from >> other execution contexts or shared memory handling problems. >> > > It's nevertheless most likely memory corruption. You can try compiling > with -gv and running your program under valgrind to see whether it finds > anything (you will probably get some false positives about certain RTL > pchar routines such as strscan and strlen, but you can ignore those). > > > Jonas > ______________________________**_________________ > fpc-pascal maillist - > fpc-pascal@lists.freepascal.**org<fpc-pascal@lists.freepascal.org> > http://lists.freepascal.org/**mailman/listinfo/fpc-pascal<http://lists.freepascal.org/mailman/listinfo/fpc-pascal> >
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