Greetings! An interesting problem I've run into: Under Linux, I have a small example program written in C (we'll call it cprog) which uses a FPC-compiled shared object library (libfpcso1.so) inside which I want to catch access violations in try/except blocks. I don't care about access violations in the C program, and by "don't care" I mean "don't care if it halts the program."
Thanks to HookSignal(RTL_SIGDEFAULT) (see http://www.freepascal.org/docs-html/rtl/sysutils/hooksignal.html) once the .so installs its signal handler, catching the exceptions in the try/except blocks works beautifully. However, if a segfault is raised in cprog, strange behavior happens. The FPC signal handler catches the signal, and goes into the "handle unhandled exception" code, which is what I wou ld expect. It raises a runtime error 217, which is what I would expect. However, it does not halt the program. What actually happens is it gets into an infinite loop of raising runtime error 217. Here's the output. Note that the first 3 lines of output are me testing that the exceptions are handled correctly in the try/except block in the .so, which they are. Then my c program causes a segfault, after which I get the infinity r.e. 217 output: =================================================== $ ./cprog handled inside so 2: Access violation handled inside so 2: Division by zero called libc, handled inside so 2: Access violation An unhandled exception occurred at $08048534 : EAccessViolation : Access violation $08048534 line 50 of cprog.c Runtime error 217 at $F7761740 $F7761740 $F77617B4 $F7783DA5 $F77647FE $F75D1BD6 $08048431 Runtime error 217 at $F7761740 $F7761740 $F77617B4 $F7783DA5 $F77647FE $F75D1BD6 $08048431 An unhandled exception occurred at $F77617EF : EAccessViolation : $F77617EF $F7783DA5 $F77647FE Runtime error 217 at $F7761740 $F7761740 Runtime error 217 at $F7761740 $F7761740 Runtime error 217 at $F7761740 $F7761740 Runtime error 217 at $F7761740 $F7761740 An unhandled exception occurred at $F77617EF : EAccessViolation : $F77617EF $F7783DA5 $F77647FE $F7783DA5 $F77647FE Runtime error 217 at $F7761740 ... (at this point it continues like this forever) =================================================== It seems the cause of this is that halt, which calls InternalExit and System_exit, which in turn calls haltproc, does not actually halt the program in the case of a library. Instead, haltproc for the library just calls InternalExit again and returns. I took my test case to an even simpler one, and simple removed the try/except block around the access violation in my test .so. So now, all my test C program is call libfpcso1.so's "crash" function and I get the infinite loop of r.e. 217's, never returning to the main program at all. I understand that it's only possible to have one signal handler installed at a time (which, in this example, I'm perfectly happy with; HookSignal does exactly what I want), but it seems wrong that an unhandled exception in a library should cause your program to go into an infinite loop, rather than doing the same thing an unhanded exception would do in an executable. Thoughts? Should I log it as a bug? Thanks, -SG -- This email is fiction. Any resemblance to actual events or persons living or dead is purely coincidental. Seth Grover sethdgrover[at]gmail[dot]com _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
