Since the kernel page tables are shared between all processes, there's
no need to (implicitly) flush the TLB for them on every context switch.
Setting the G bit on kernel page tables allows the CPU to keep the
translation caches around.
After we clear the FPU state in a thread when it uses the FPU for the
first time, we also save the clean slate in the thread's FPU state
buffer. When we're doing that, let's write through current->fpu_state()
just to make it clear what's going on.
It was actually safe, since we'd just overwritten the g_last_fpu_thread
pointer anyway, but this patch improves the communication of intent.
Spotted by Bryan Steele, thanks!
Cloned threads (basically, forked processes) inherit the complete FPU
state of their origin thread. There was a bug in the lazy FPU state
save/restore mechanism where a cloned thread would believe it had a
buffer full of valid FPU state (because the inherited flag said so)
but the origin thread had never actually copied any FPU state into it.
This patch fixes that by forcing out an FPU state save after doing
the initial FPU initialization (FNINIT) in a thread. :^)
Now programs can catch the SIGSEGV signal when they segfault.
This commit also introduced the send_urgent_signal_to_self method,
which is needed to send signals to a thread when handling exceptions
caused by the same thread.
Added the exception_code field to RegisterDump, removing the need
for RegisterDumpWithExceptionCode. To accomplish this, I had to
push a dummy exception code during some interrupt entries to properly
pad out the RegisterDump. Note that we also needed to change some code
in sys$sigreturn to deal with the new RegisterDump layout.
If we receive an IRQ while the idle task is running, prevent it from
re-halting the CPU after the IRQ handler returns.
Instead have the idle task yield to the scheduler, so we can see if
the IRQ has unblocked something.
Due to the changes in signal handling m_kernel_stack_for_signal_handler_region
and m_signal_stack_user_region are no longer necessary, and so, have been
removed. I've also removed the similarly reduntant m_tss_to_resume_kernel.
Instead of PDE's and PTE's being weird wrappers around dword*, just have
MemoryManager::ensure_pte() return a PageDirectoryEntry&, which in turn has
a PageTableEntry* entries().
I've been trying to understand how things ended up this way, and I suspect
it was because I inadvertently invoked the PageDirectoryEntry copy ctor in
the original work on this, which must have made me very confused..
Anyways, now things are a bit saner and we can move forward towards a better
future, etc. :^)
We'll now try to detect crashes that were due to dereferencing nullptr,
uninitialized malloc() memory, or recently free()'d memory.
It's not perfect but I think it's pretty good. :^)
Also added some color to the most important parts of the crash log,
and added some more modes to /bin/crash for exercising this code.
Fixes#243.
