Hello L4 hackers, I hope you are all doing well today.
I am hoping to discuss the topic of threads to better my understanding of it,
as it seems to be a major building block in L4Re. I have the following
questions (using the c++ based libraries.):
1. Is Pthread the official way to create threads in an L4Re application?
2. I have made a L4 thread (to understand how threads work in L4) without the
help of pthreads by setting up the Attr, which involved in setting the
exception handlers(using rm()), pager (using rm()), instruction pointers, stack
pointers, binding, ex_reg() and finally running. All seems well until I try
printing a message.
It seems seems I am unable to use the printf() function in the instruction
pointer function of said thread. The error I get is :
ttest | l4re_itas[rm]: unhandled read page fault at 0x141 pc=0x100f8a0
ttest | l4re_itas: rom/thread_test: Unhandled exception: PC=0x100f8a0
PFA=0x140 LdrFlgs=0x0
However, if I use printf in a pthread, none of these errors pop up.
2a. Am I using the wrong exception handler and pager (I got both from rm)?
2b. Also, the "l4_vcon_send(L4_BASE_LOG_CAP,..,...) function seems to work
fine in either case, shouldn't printf() eventually call this function as
after a series of indirections?
2c. What exc_handler and pager do pthreads use? Why are they able to handle
the pager faults and exceptions from printf? Can I appropriate
them for the L4 threads I started?
3. It seems the Virtual Machines (VMs) that are on the hypervisor are also
closely related with threads. I assume these are Vcpu threads and not pthreads.
3a. Am I correct in this assumption?
3b. How are the exception handlers and pagers set up for these Vcpus?
Thank you so much for your time,
David
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