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Re: GSOC - Valgrind for Hurd


From: Samuel Thibault
Subject: Re: GSOC - Valgrind for Hurd
Date: Tue, 20 May 2014 22:50:07 +0200
User-agent: Mutt/1.5.21+34 (58baf7c9f32f) (2010-12-30)

Hello,

I would advise starting with trivial system calls, such as
mach_thread_self, mach_task_self, and mach_host_self, which don't take
any parameter, and just returns a port. That'll make you implement the
basic infrastructure for the trap call.

Then calls like task_terminate, task_suspend, etc., i.e. calls which
only take parameters and return a value, should be a matter of
explaining valgrind how parameters are passed to the kernel during the
trap.

Then calls like task_create or mach_port_allocate, i.e. calls which
return a value through a pointer, should be quite easy.  At that point
you should be able to easily implement almost all of the system calls.
This won't be enough to run even a mere main() {} program, since libc
itself uses RPCs, but getting that infrastructure right will already be
plenty.

Then more hard stuff will come: vm_map, vm_allocate, vm_deallocate.  One
will have to tell valgrind that these initialize or destroy a whole
area of memory.  And last but not least, mach_msg_trap will be the most
complex one.  You'll have to precisely check how the mach_msg_header_t
is dealt with according to flags etc. If that does not fit the gsoc,
I'd say it's not a problem, we can probably help you with it, once the
infrastructure is settled.

Samuel



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