Note that there seems to be a deadlock if a process exits when there are
zombies around. Init also doesn't handle zombie children correctly as there
is sent no SIGCHLD signal yet.
This helps running cross compiled programs as well as compiling programs
under Sortix with gcc. There is also support for global constructors.
Currently, cross-compiled executables uses these startup files. The current
build system continues to use start.o, which does not offer global
constructors and other useful features.
Note that these using the crtX.o files requires the crtbegin.o and crtend.o
files that ship with the cross compiler, but that should be no problem.
There are still a few non-standard quirks and things that needs to be
properly implemented but that shouldn't be too hard and the most important
features are now implemented.
This is a rather stupid implementation as it does the search in linear
time. More importantly, it is correct and helps porting gcc. Besides, it
can easily be fixed in due time.
This violates POSIX but POSIX is stupid in this respect. Of course, this
will ever so subtly break some applications. Not sure how this stupid design
can be fixed without breaking backwards compatibility. Perhaps remove the
putenv(3) function and replace it with a better replacement? (Or perhaps you
should just use setenv(3) anyways..)
This helps gcc build since it assumes that string.h provides various
functions that POSIX mandates is in strings.h. This is OK with me since that
strings.h is a nasty hack anyways. Also, glibc does this.
This caused a corruption of the resulting file if the program fwrite some
data that is buffered, then fseeks, and then fflushes. The fwrite will then
happen at the wrong memory location. Flushing in fseeko(3) fixes the problem
but it may cause violate some standard or just be inefficient.
Previously fread and fwrite for file descriptors would return the number of
bytes read/written rather than the number of elements read/written. This
breaks the C standard and broke various third party programs such as
readelf from binutils.
Removed Maxsi::Process:: functions as they suck and are barely used. Gave
the functions standard names and put them in their own source files.
The declarations now have nice noreturn attributes attached.
It's a much better name if you think of it as task-fork or thread-fork in the
sense that it either modifies this task or creates a new one. This call will
be used to provide user-space threads as well as fork(2).
This code uses the cr0 task switched bit to disable the FPU upon task
switch, which allows the kernel to delay copying the registers until
another task starts using them. Or better yet, if no other thread actually
uses the registers, then it won't need to do any copying at all!
Note that the scheduler does not load/restore floating point numbers yet
upon task switching. This means only one task can use floating point numbers
at the same time without the risk of race conditions.
Note that this enables SSE in 32-bit x86 platforms - but not all models
have such support, which limits which computers Sortix works on. Ideally, we
should detect what features are available on the computer at runtime and
enable/disable the proper kernel support. This is not a problem on x86_64.
Pardon the big ass-commit, this took months to develop and debug and the
refactoring got so far that a clean merge became impossible. The good news
is that this commit does quite a bit of cleaning up and generally improves
the kernel quality.
This makes the kernel fully pre-emptive and multithreaded. This was done
by rewriting the interrupt code, the scheduler, introducing new threading
primitives, and rewriting large parts of the kernel. During the past few
commits the kernel has had its device drivers thread secured; this commit
thread secures large parts of the core kernel. There still remains some
parts of the kernel that is _not_ thread secured, but this is not a problem
at this point. Each user-space thread has an associated kernel stack that
it uses when it goes into kernel mode. This stack is by default 8 KiB since
that value works for me and is also used by Linux. Strange things tends to
happen on x86 in case of a stack overflow - there is no ideal way to catch
such a situation right now.
The system call conventions were changed, too. The %edx register is now
used to provide the errno value of the call, instead of the kernel writing
it into a registered global variable. The system call code has also been
updated to better reflect the native calling conventions: not all registers
have to be preserved. This makes system calls faster and simplifies the
assembly. In the kernel, there is no longer the event.h header or the hacky
method of 'resuming system calls' that closely resembles cooperative
multitasking. If a system call wants to block, it should just block.
The signal handling was also improved significantly. At this point, signals
cannot interrupt kernel threads (but can always interrupt user-space threads
if enabled), which introduces some problems with how a SIGINT could
interrupt a blocking read, for instance. This commit introduces and uses a
number of new primitives such as kthread_lock_mutex_signal() that attempts
to get the lock but fails if a signal is pending. In this manner, the kernel
is safer as kernel threads cannot be shut down inconveniently, but in return
for complexity as blocking operations must check they if they should fail.
Process exiting has also been refactored significantly. The _exit(2) system
call sets the exit code and sends SIGKILL to all the threads in the process.
Once all the threads have cleaned themselves up and exited, a worker thread
calls the process's LastPrayer() method that unmaps memory, deletes the
address space, notifies the parent, etc. This provides a very robust way to
terminate processes as even half-constructed processes (during a failing fork
for instance) can be gracefully terminated.
I have introduced a number of kernel threads to help avoid threading problems
and simplify kernel design. For instance, there is now a functional generic
kernel worker thread that any kernel thread can schedule jobs for. Interrupt
handlers run with interrupts off (hence they cannot call kthread_ functions
as it may deadlock the system if another thread holds the lock) therefore
they cannot use the standard kernel worker threads. Instead, they use a
special purpose interrupt worker thread that works much like the generic one
expect that interrupt handlers can safely queue work with interrupts off.
Note that this also means that interrupt handlers cannot allocate memory or
print to the kernel log/screen as such mechanisms uses locks. I'll introduce
a lock free algorithm for such cases later on.
The boot process has also changed. The original kernel init thread in
kernel.cpp creates a new bootstrap thread and becomes the system idle thread.
Note that pid=0 now means the kernel, as there is no longer a system idle
process. The bootstrap thread launches all the kernel worker threads and then
creates a new process and loads /bin/init into it and then creates a thread
in pid=1, which starts the system. The bootstrap thread then quietly waits
for pid=1 to exit after which it shuts down/reboots/panics the system.
In general, the introduction of race conditions and dead locks have forced me
to revise a lot of the design and make sure it was thread secure. Since early
parts of the kernel was quite hacky, I had to refactor such code. So it seems
that the risk of dead locks forces me to write better code.
Note that a real preemptive multithreaded kernel simplifies the construction
of blocking system calls. My hope is that this will trigger a clean up of
the filesystem code that current is almost beyond repair.
Almost all of the kernel was modified during this refactoring. To the extent
possible, these changes have been backported to older non-multithreaded
kernel, but many changes were tightly coupled and went into this commit.
Of interest is the implementation of the kthread_ api based on the design
of pthreads; this library allows easy synchronization mechanisms and
includes C++-style scoped locks. This commit also introduces new worker
threads and tested mechanisms for interrupt handlers to schedule work in a
kernel worker thread.
A lot of code have been rewritten from scratch and has become a lot more
stable and correct.
Share and enjoy!
Jonas 'Sortie' Termansen