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vsprintf().
Coverted all printk()/printf() functions to capatalised hex for
readability.
Tidied up some code.
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Implemented the sprintf() library function in lib/stdio.c which uses the
vsprintf() function.
Implemented a very primative controlling TTY for each process. This is
achieved by a switch in the sys_puts system call which uses the 'ctty'
element of the process' task structure to determine an appropriate I/O
channel. A negative ctty value doesn't equate to any I/O channel
effectively disabling the process' output.
Added the sys_ctty system call which allows a process to set it's own
ctty value.
Removed the sys_rsputs system call. Output to serial is now performed by
the process first setting it's ctty value to 1, then invoking sys_puts.
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a pointer to the saved state information to check_signals(). This bug
would have only manifested itself if multiple signals were to be
processed (sigret) or if a signal had been set during the handling of a
timer interrupt (tick_handler) and *ONLY* if switching to the user's own
handler since the state information is not needed to invoke the kernel's
default signal handler.
Implemented alarms for userspace processes. This required significant
modification of the scheduler algorithm. When idling waiting for a
process that can run, the scheduler now continually checks the alarms
and signals of each process and updates their state accordingly.
Implemented the sys_alarm system call to set the new 'alarm' field for
the calling process.
Created the sys_pause system call which changes the state of the calling
process to TSTATE_INTERRUPTIBLE, effectively removing it from the
scheduler's run queue, putting it to sleep until a signal arrives.
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the IDT. This function takes the same parameters as register_isr() which
creates interrupt gate entries in the IDT.
The register_isr() function now sets the gate type to 0x0E regardless of
what was already in the descriptor. This is to break reliance on the IDT
already being initialized to a known state as well as avoiding conflicts
with the new register_trap() function.
Added declaration for the 'ticks' variable in kernel/sched.h so that
it's value may be used throughout the kernel.
Changed the system call gate to a trap gate. This means that interrupts
will not be disabled prior to entry into the system call handler. This
will allow hardware functions such as the timer to operate continuously
even if the user makes a system call.
Added checks to the timer interrupt handler. These checks prevent the
scheduler from being called if the interrupt occurred during kernel mode
execution. The idea here, is that the timer interrupt handler only
services the hardware (increments the tick count and sends an EOI to the
PIC's) if a system call was already running in the kernel. The system
call handler has also been expanded to check if the timer fired prior to
returning to userspace. If the timer did fire, the syscall handler will
invoke the scheduler (as the timer handler would have), so that it can
decide if it's time to switch tasks.
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prior to return. This meant that switching to the same task did not
abort properly as the incorrect return address was popped off the stack.
Fixed a bug where the task register was not initialized before the
scheduler. This meant that on the first task switch, the CPU would dump
it's current state to a random address (0 most likely), potentially
corrupting important data. This has been corrected by introducing a
'garbage TSS' (and associated descriptor in the GDT) which is selected
before the scheduler is initialized as a safe place for the data to be
written.
Modified the scheduler so that it now waits indefinitely until a task
becomes ready to run. This fixes the possible bug where the scheduler
won't re-schedule the currently running task if it is the only task on
the system.
Add signal handling capabilities to the kernel. The bulk of this is
present in the subroutine check_signals() defined in traps.s. This
function is called on every timer tick and system call prior to
userspace return. The subroutine operates by pushing fake state
information onto the kernel's stack, then using it to return to
userspace. Prior to this, the subroutine pushes the return address
0xFFFFE000 onto the user's stack. This address corresponds to the
unmapped page located between the top of the user's stack (lower) and
the kernel's stack page (upper). When the user's signal handler tries to
return, it will cause a page fault that will be used as a notification
mechanism to inform the kernel that the signal handler is done. The
kernel will then switch to the originally pushed state information and
use it to return the task to the original execution state. Due to it's
nature, check_signals() must only be called prior to exiting the kernel
since it may not return.
Added the header file 'signal.h' which defines (most) of the POSIX
signals as well as the prototype for the signal() function.
Added the 'signal' element to the task structure. This field is a bitmap
of all currently pending signals.
Added the 'sig_handlers' element to the task structure. This is an array
of all user-defined signal handlers. Currently, a value of 0 indicates
the default handler should be used whilst any other value is considered
to be the address of a userspace signal handler. The ability to ignore a
signal is not yet present but will be added sometime soon.
Added the sys_signal system call to register a signal.
Added the stub function sighandler_default() to sched.c which handles
all signals not caught by the user.
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each structure has a TSS inside, as well as several descriptor entries
in the GDT pointing to each task's TSS. Task switching is performed in
hardware by means of far jumping to the new task's TSS descriptor in the
GDT. Task states are saved manually by copying the saved state from the
interrupt handler's stack, back into the task's TSS.
Added the function save_state() to sched.c which can be called from
assembly to copy the state information of the suspended task from the
current stack, to it's respective task structure. NOTE: this assumes
that the pointer cstate has been set ahead of time to point to the state
information on the stack, and that the pointer ctask has not yet been
modified.
Added the function reschedule() which is currently called from the
timer's tick handler. Currently, this function merely alternates between
the two tasks created in sched_init(), but in future, will be expanded
to decided independently which task will run next.
The function userspace_init() was renamed to the more appropriate
sched_init().
Moved most of the code from the original userspace_init() to the new
function create_proc() which sets up a virtual address space and state
information, copies the specified binary into the new address space,
then returns a pointer to the newly created tasks entry in the task
table.
Defined the type pid_t in unistd.h as a 16-bit unsigned integer.
Added two new debugging system calls for checking which task is
currently active. The getpid() system calls returns the caller's PID
whilst the getpdir() call returns the physical location of the caller's
page directory (the value of CR3). The getpdir() call can be used as a
fallback to determine which task is *actually* running if the
information in ctask or the getpid() call is faulty.
Added two new subroutines; set_tss() and clear_tss() (whose prototypes
are defined in asm/system.h) for managing the task-state descriptor
entries in the GDT. set_tss() initializes a TSS descriptor and sets it's
base pointer to the supplied TSS pointer whilst clear_tss() simply marks
a TSS descriptor as 'not present' without clearing it.
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vsprintf() function to render formatted strings and then the puts system
call to output them.
Moved the vsprintf() function from the kernel to the library.
Furthermore, the prototype for the function has been moved from the
kernel's headers, to the new header file stdio.h.
Renamed the kernel's internal printf() function to printk() in order to
avoid confusion with the library provided function.
Renamed the sys_print system call to the more appropriate name,
sys_puts.
Added a new system call sys_time, which returns the system's uptime in
seconds. This is mainly for testing the userspace binary and will not be
permanent.
Added the file time.c to the library which contains the caller for
sys_time and a helper routine sleep() which delays execution for the
specified number of seconds. The new header file time.h contains
prototypes for both these functions as well as the definition for the
type time_t.
Fixed a bug in which the value of EAX was not properly passed to the
system call handler, resulting in the wrong system call being executed.
This was caused by the code in the SAVE macro not properly preserving
the value.
Fixed a bug in which the value of EAX was not preserved during a return
from system call, but rather restored with the original EAX value prior
to the call. As a result, system call return codes were not properly
passed. This has been corrected by introducing a new macro RESTORE_SYS
which carries out the same restore operations, but maintains EAX prior
to the return.
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assembly function register_isr making it usable within the C portions of
the source.
Added a new file panic.s with the function panic that will print a panic
message, disable interrupts and halt the system.
Created the skeleton framework for paging in the new file page.s. The
new function paging_init (called in kboot) will setup a simple page
directory with two tables covering all addresses 0-8MB. It will also
mark pages from 0-1MB as 'supervisor-only' to protect the kernel. NOTE:
The function paging_init must be called before initialising the IDT as
it does not disable interrupts!
Modified the page fault handler to print the offending linear address
along with the supplied error code. Following that, the handler will
initiate a kernel panic. This function (along with panic) assumes
console I/O to be operational.
Modified the userspace test code to deliberately intiate a page fault by
accessing an unmapped page.
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invoking the tool recursively.
Disabled GCC's position-independent-code generation in makefiles.
Modified makefile for kernel/usrbin so that it now compiles and links C
code into the userspace test.
Created errno.h and populated it with standard error definitions.
Replaced the va_list based system call handlers with a system call table
defined in the header kernel/sys.h. NOTE: This header is included in
kmain.c and should ONLY be included there! Do NOT include this header in
sys.c.
Rather than fetching the user's stack pointer and using it to initialize
a va_list, parameters are now passed to the call handlers via the
general purpose registers EAX, EBX, ECX and EDX where EAX contains the
requested call number and conveys the return value.
Setup macros in unistd.h to aid to making system calls from userspace.
Implemented two basic system calls; sys_print and sys_dummy. The former
takes a single char* argument and displays it on screen whilst the
latter is used to populate otherwise empty entries of the system call
table. sys_dummy returns the error ENOSYS whenever it is called.
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32-255. A separate routine in the new file traps.s initializes the first
32 entries with addresses pointing to exception handlers within said
file.
Modified the register_isr function to now accept a descriptor privilege
level which it will assign to the modified IDT entry.
Added a task state segment and corresponding entry to the GDT. The TSS
will store the kernel's stack pointer and stack segment when switching
to userspace. NOTE: The stack pointer MUST be saved manually before
switching to userspace!
Added the framework for a system call interface at interrupt vector 0x80
(128).
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