siginfo_t content

[John Baldwin]

On 2/15/19 8:43 AM, Christian Barthel wrote:
> John Baldwin <jhb at FreeBSD.org> writes:
> 
>> See the siginfo(3) manpage.  SI_TIMER is described there as:
>>
>>     SI_TIMER             signal generated by expiration of a
>>                          timer set by timer_settime(2)
>>
>> It is not for setitimer.  Similarly, si_addr is usually only specified for
>> synchronous signals and usually holds the PC of the faulting instruction
>> except for SIGSEGV when it holds the faulting virtual address.
> 
> Thanks for your reply. 
> Ah, yes, siginfo(3) has more details on siginfo_t (missed that
> one; sorry).  This clarifies my question.
> I've looked up the POSIX standard but I haven't seen a reason why
> si_addr is only set for SIGSEGV and "only" a few others - are
> there reasons for this?

I think it's only intended for use with synchronous traps where the signal
is the result of executing an instruction (so si_addr is usually the PC of
the instruction triggering the signal).  Async events like timers aren't
triggered by instructions, so there's no meaningful si_addr to use.

However, in a signal handler you can look at the architecture-specific
ucontext_t * (3rd argument to handler when using SA_SIGINFO) to determine
the PC of the thread at the time it was interrupted by the signal.

What are you trying to do exactly?

-- 
John Baldwin