Subject: Re: SIGTRAP for traced processes and COMPAT_MACH
To: Matthew Orgass <email@example.com>
From: Emmanuel Dreyfus <firstname.lastname@example.org>
Date: 11/30/2003 11:01:42
Matthew Orgass <email@example.com> wrote:
> Why would darwin_trapsignal call trapsignal if a mach exception is
> raised? I thought the point of this is to not do so.
darwin_trapsignal calls trapsignal if no Mach exception was generated,
so that a signal can be sent.
> Since kpsignal2 is static this is better there, but I don't see how it
> would benefit trapsignal.
signals sent by traps for illegal instruction, memory fault and many
others are sent through trapsignal. trapsignal can call do
kpsignal/kpsignal1/kpsignal2 chain, or it can directly call kpsendsig
for an immediate signal delivery.
If we interecept the signal in kpsignal2, we need to intercept it in
> Also, should kevents be sent if a Mach exception is raised?
I see no need for this now... Only compatibility code is interested into
> So: does this really need to apply generally to all signals? If not,
> the origional idea of just calling e_trapsignal for SIGTRAP would seem to
> make the most sense.
Yes. Darwin has yet another weird feature called softsignal. You request
it using ptrace(PT_SIGEXC, 0, 0, 0);
Once you did that, any signal (except non catchable signal such as
SIGKILL or SIGSTOP, of course) is inhibited, and a Mach exception is
sent in place of the signal.
The Mach exception is sent to the port registered for EXC_SOFTWARE
exceptions. The exception message contains a code array, with code =
SOFT_SIGNAL and code set to the signal number. More code elements may
be used for siginfo information, I have not checked that yet.
Darwin's gdb uses that feature: it gets any signal to the traced process
as a Mach exception. In order to emulate this, any call to [k]psignal in
the kernel should be intercepted by COMPAT_MACH code to eventually
generate a Mach exception and inhibit the signal delivery.
I implemented my yesterday's proposal (an emulation hooked cheksignal
function in kpsignal2 and trapsignal), and this works fine. I'm awaiting
for opinions about this before committing it...
Il y a 10 sortes de personnes dans le monde: ceux qui comprennent
le binaire et ceux qui ne le comprennent pas.