SPI_prepare and error recovery

I'm using SPI_prepare to do some dynamic SQL stuff in the backend. Some
errors result in a call to the elog routines with ERROR level, which in turn
causes log printout and a longjmp. Since I want to trap those errors and try
an alternative I tried the following:

sigjmp_buf saveRestart;
memcpy(&saveRestart, &Warn_restart, sizeof(saveRestart));
if(sigsetjmp(Warn_restart, 1) != 0)
{
memcpy(&Warn_restart, &saveRestart, sizeof(Warn_restart));
/* Handle error here */
return NULL;
}
void* plan = SPI_prepare(...);
memcpy(&Warn_restart, &saveRestart, sizeof(Warn_restart));
return plan;

My question is, at the point of /* Handle error here */, how do I get hold
of the error information? Judging from the code in elog.c, this info is sent
do the server and/or client log and then lost before the longjmp is made. Is
that the way it's supposed to be?

Regards,

Thomas Hallgren