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CPU is not an i386 before executing the invlpg instruction with the
provided address. This will once again make the kernel compatible with
the i386 processor as executing the invlpg instruction without these
checks would have resulted in an invalid opcode exception.
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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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is produced. This may change later.
Added the new directory 'lib' to the source tree which build lib.a, an
archive containing common library routines for both the kernel and
userspace code to use.
Added the file string.c to the lib directory (as well as the appropriate
headers in /include) which provides some basic functions from the
standard C string library.
Added a physical memory manager which is now located in memory.c. This
memory manager tracks free pages from 1MB-8MB with a simple table and
allocates memory in blocks of 4KB pages. Multiple pages can be allocated
in which they are returned as a linked list.
Added a 'page window' in memory.c which allows the temporary mapping of
a single page at a time into the current address space.
Moved all paging routines that were previously located in page.s over to
memory.c where they have been re-implemented as a mixture of C and
inline assembly.
Moved the primative userspace routines from usrspace.s over to the new
sched.c. The only remaining routine, usrcall is now located in asm.s as
'switch_to' which takes two arguments, pointers to the task structure
and task state structure of the new task which is being switched to.
Pages for userspace are now allocated dynamically. The user binary is
loaded in at 1GB upwards. The user stack is located at the end of the
4GB address space with the lower 1GB being reserved for the kernel.
Updated the link.ld file for the userspace binary to include the new
starting address 0x40000000 (1GB).
Renamed the symbols for the user binary blob to make them shorter.
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