SIGBUS or SIGSEGV on OSX?

[Vladimir Kozlov]

So we have it in BSD port but not in OSX? That would explain it, I did review of 
  BSD port and thought that OSX will use the same code.

Thank you, Roland, for finding it.

Vladimir

Roland Westrelin wrote:
> Hi,
> 
> We (the compiler team) had a couple of bugs reported on OSX where the crash is caused by a SIGBUS in a compiled method:
> 
> siginfo:si_signo=SIGBUS: si_errno=0, si_code=2 (BUS_ADRERR), si_addr=0x0000000115d4f018
> 
> The 64 bit VM is running in "compressed oops with base" mode. The base is 0x0000000115d4f000.
> The address of the erroneous memory access is 8 byte aligned and falls in the first page of the heap which is used for implicit null checks. So this access is not expected to trigger a SIGBUS but rather a SIGSEGV and should then be handled by hotspot rather than lead to a crash.
> 
> I see in JVM_handle_bsd_signal() that there's a number of places where a test for SIGSEGV was replaced by test for a SIGSEGV or a SIGBUS. In particular, I think this:
> 
> #if defined(__APPLE__) && !defined(AMD64)
>       // 32-bit Darwin reports a SIGBUS for nearly all memory access exceptions.                                                                                                                                                                                                
>       // Catching SIGBUS here prevents the implicit SIGBUS NULL check below from                                                                                                                                                                                                
>       // being called, so only do so if the implicit NULL check is not necessary.                                                                                                                                                                                                
>       } else if (sig == SIGBUS && MacroAssembler::needs_explicit_null_check((int)info->si_addr)) {
> #else
>       } else if (sig == SIGBUS /* && info->si_code == BUS_OBJERR */) {
> #endif
> 
> would fix the problem on 64 bit as well.
> 
> Should I make this change?
> 
> Roland.