[racket] FFI crashing Racket

It appears, from some quick googling, that createIndex enables
multithreading in clang, which might explain this, depending on the
threading libraries used.

Sam
On Oct 19, 2014 9:24 AM, "Matthew Flatt" <mflatt at cs.utah.edu> wrote:

> It appears that calling clang_createIndex() sets the handler for
> SIGSEGV, which interferes with Racket's own SIGSEGV handler to
> implement the GC's write barrier.
>
> The program below illustrates. It sets the handler before and after a
> call to clang_createIndex() and shows that the handler has been changed
> after the call. If you comment out the clang_createIndex() call, then
> the handler is unchanged.
>
> I have no idea why clang_createIndex() would set the SIGSEGV handler or
> whether that can be disabled.
>
> ----------------------------------------
>
> #include <stdio.h>
> #include <string.h>
> #include <signal.h>
> #include <sys/types.h>
> #include <unistd.h>
>
> typedef void *CXIndex;
> extern CXIndex clang_createIndex(int, int);
>
> void fault_handler()
> {
>   printf("fault\n");
> }
>
> void check()
> {
>   struct sigaction act, oact;
>   memset(&act, 0, sizeof(act));
>   act.sa_sigaction = fault_handler;
>   sigemptyset(&act.sa_mask);
>   sigaction(SIGSEGV, &act, &oact);
>
>   printf("%p %d\n", oact.sa_sigaction, oact.sa_sigaction == fault_handler);
> }
>
> int main() {
>   void *dl;
>
>   check();
>
>   clang_createIndex(0, 0);
>
>   check();
>
>   return 0;
> }
>
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