Neale Ferguson wrote: >When a signal like SIGSEGV or SIGFPE is intercepted by a signal handler >that receives signal no., siginfo_t, and ucontext the PSW is that of the >program old PSW. However, the instruction length code (ILC) is not >passed anywhere nor can is it accessible (nor could it be relied upon) >from low-core. This makes writing signal handlers that inspect the >problem difficult. For example, I want to distinguish between a zero >divide exception and other fixed point exceptions (both PROG 009). I'd >like to inspect the opcode to see if it was a divide operations and then >check the operands to see if the divisor was 0. The divide instruction >could be 2, 4, or 6 bytes long (RR, RX, RXY format) but because the PSW >address is pointing to the instruction following and there's no ILC I >cannot write a foolproof method of finding the opcode (having 1d20 could >be the opcode for DR but it might be part of the displacement field of >the D, DL instructions). I'd like to suggest that the ucontext structure >be enhanced to include the ILC information. (Changing the current >behavior of the PSW address would probably cause massive breakage.)
Changing ucontext would cause significant ABI issues, so we like to avoid that if at all possible ;-) In any case, for those signals where the PSW address points after the faulting instruction, the siginfo_t always contains a field si_addr which holds the address of the faulting insn itself. This can be used for purposes like the one you describe. There has been a little bit of confusion about just when the PSW points to or after the current instruction in the past, but the rule (that current 2.6 kernels enforce) is: SIGILL/SIGFPE/SIGTRAP point after the instruction, every other signal points to the instruction. For an example of how to handle your very problem (analysing SIGFPEs resulting from divide), you may have a look at libjava/include/s390-signal.h (HANDLE_DIVIDE_OVERFLOW) residing in current GCC sources. Mit freundlichen Gruessen / Best Regards Ulrich Weigand -- Dr. Ulrich Weigand Linux for S/390 Design & Development IBM Deutschland Entwicklung GmbH, Schoenaicher Str. 220, 71032 Boeblingen Phone: +49-7031/16-3727 --- Email: [EMAIL PROTECTED] ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
