Yo Hal! On Fri, 02 Jun 2017 03:54:20 -0700 Hal Murray <[email protected]> wrote:
> > Which also commented oout stuff needed in the SIGALRM handler,
> > which created the double trap.
>
> How much does the handler need?
What do you mean 'need'?
> Is there a pile of stuff needed
> before we get to catchTrap?
Zero stuff. We never call catchTrap(), the seccomp code calls
catchTrap().
> The first thing that catchTrap does is
> call msyslog and we already know that works since it prints the
> seccomp-worked message.
Yup. Sort of, I have seen weirdness in that area. mysyslog()
will behave differently inside a trap. Many syscalls, and lib calls,
are not legal in a trap.
> Trapping on recvfrom works.
>
> 2 Jun 03:27:58 ntpd[25506]: ERROR: SIGSYS: got a trap.
> 2 Jun 03:27:58 ntpd[25506]: ERROR: SIGSYS/seccomp bad syscall
> 45/0xc000003e 2 Jun 03:27:58 ntpd[25506]: 0.0.0.0 c01d 0d kern kernel
> time sync disabled
>
> The 45 is recvfrom. I don't know what the second number is good for.
The second number is si_arch. Some libc can make two different types
of syscalls. For example i386 and x64 syscalls are very different.
So a type 45 in i386 may be different than a type 45 in x86.
More details in the syscall and signal man pages.
> I tried a bit, commenting out some of the syscalls in the DNS ifdef.
> Sometimes it works, sometimes it doesn't. I didn't find a pattern.
> It's not a simple it needs "this one".
Yup, not simple.
Just a WAG: maybe some failed syscalls are in non-reentrant code
that the backtrace/mysyslog need?
RGDS
GARY
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