- if an exception occurs in kernel and this exception is not handled
in an sane way and the kernel crashes, it also dumps what was loaded
in the general purpose registers exactly at the time of the
exception to help to debug the problem
the kernel. They are not used atm, but having them in trunk allows them
to be easily used when needed. To set a breakpoint that triggers when
the variable foo is written to (the most common use case), one calls:
breakpoint_set(vir2phys((vir_bytes) &foo), 0,
BREAKPOINT_FLAG_MODE_GLOBAL |
BREAKPOINT_FLAG_RW_WRITE |
BREAKPOINT_FLAG_LEN_4);
It can later be disabled using:
breakpoint_set(vir2phys((vir_bytes) &foo), 0,
BREAKPOINT_FLAG_MODE_OFF);
There are some limitations:
- There are at most four breakpoints (hardware limit); the index of the
breakpoint (0-3) is specified as the second parameter of
breakpoint_set.
- The breakpoint exception in the kernel is not handled and causes a
panic; it would be reasonably easy to change this by inspecing DR6,
printing a message, disabling the breakpoint and continuing. However,
in my experience even just a panic can be very useful.
- Breakpoints can be set only in the part of the address space that is
in every page table. It is useful for the kernel, but to use this for
user processes would require saving and restoring the debug registers
as part of the context switch. Although the CPU provides support for
local breakpoints (I implemened this as BREAKPOINT_FLAG_LOCAL) they
only work if task switching is used.
forget about the dirtypde bitmap and WIPEPDE/DONEPDE macros too.
check if mapping happens to already be in place, and if so, don't
reload cr3 (on the account of that mapping, that is).
don't reload cr3 unconditionally.
UPDATING INFO:
20100317:
/usr/src/etc/system.conf updated to ignore default kernel calls: copy
it (or merge it) to /etc/system.conf.
The hello driver (/dev/hello) added to the distribution:
# cd /usr/src/commands/scripts && make clean install
# cd /dev && MAKEDEV hello
KERNEL CHANGES:
- Generic signal handling support. The kernel no longer assumes PM as a signal
manager for every process. The signal manager of a given process can now be
specified in its privilege slot. When a signal has to be delivered, the kernel
performs the lookup and forwards the signal to the appropriate signal manager.
PM is the default signal manager for user processes, RS is the default signal
manager for system processes. To enable ptrace()ing for system processes, it
is sufficient to change the default signal manager to PM. This will temporarily
disable crash recovery, though.
- sys_exit() is now split into sys_exit() (i.e. exit() for system processes,
which generates a self-termination signal), and sys_clear() (i.e. used by PM
to ask the kernel to clear a process slot when a process exits).
- Added a new kernel call (i.e. sys_update()) to swap two process slots and
implement live update.
PM CHANGES:
- Posix signal handling is no longer allowed for system processes. System
signals are split into two fixed categories: termination and non-termination
signals. When a non-termination signaled is processed, PM transforms the signal
into an IPC message and delivers the message to the system process. When a
termination signal is processed, PM terminates the process.
- PM no longer assumes itself as the signal manager for system processes. It now
makes sure that every system signal goes through the kernel before being
actually processes. The kernel will then dispatch the signal to the appropriate
signal manager which may or may not be PM.
SYSLIB CHANGES:
- Simplified SEF init and LU callbacks.
- Added additional predefined SEF callbacks to debug crash recovery and
live update.
- Fixed a temporary ack in the SEF init protocol. SEF init reply is now
completely synchronous.
- Added SEF signal event type to provide a uniform interface for system
processes to deal with signals. A sef_cb_signal_handler() callback is
available for system processes to handle every received signal. A
sef_cb_signal_manager() callback is used by signal managers to process
system signals on behalf of the kernel.
- Fixed a few bugs with memory mapping and DS.
VM CHANGES:
- Page faults and memory requests coming from the kernel are now implemented
using signals.
- Added a new VM call to swap two process slots and implement live update.
- The call is used by RS at update time and in turn invokes the kernel call
sys_update().
RS CHANGES:
- RS has been reworked with a better functional decomposition.
- Better kernel call masks. com.h now defines the set of very basic kernel calls
every system service is allowed to use. This makes system.conf simpler and
easier to maintain. In addition, this guarantees a higher level of isolation
for system libraries that use one or more kernel calls internally (e.g. printf).
- RS is the default signal manager for system processes. By default, RS
intercepts every signal delivered to every system process. This makes crash
recovery possible before bringing PM and friends in the loop.
- RS now supports fast rollback when something goes wrong while initializing
the new version during a live update.
- Live update is now implemented by keeping the two versions side-by-side and
swapping the process slots when the old version is ready to update.
- Crash recovery is now implemented by keeping the two versions side-by-side
and cleaning up the old version only when the recovery process is complete.
DS CHANGES:
- Fixed a bug when the process doing ds_publish() or ds_delete() is not known
by DS.
- Fixed the completely broken support for strings. String publishing is now
implemented in the system library and simply wraps publishing of memory ranges.
Ideally, we should adopt a similar approach for other data types as well.
- Test suite fixed.
DRIVER CHANGES:
- The hello driver has been added to the Minix distribution to demonstrate basic
live update and crash recovery functionalities.
- Other drivers have been adapted to conform the new SEF interface.
swapcontext, and makecontext).
- Fix VM to not erroneously think the stack segment and data segment have
collided when a user-space thread invokes brk().
- Add test51 to test ucontext functionality.
- Add man pages for ucontext system calls.
implementations for these functions, we lean on GNU builtin functions
for using them, so these declarations are also conditional on using
a GNU compiler.
Move archtypes.h to include/ dir, since several servers require it. Move
fpu.h and stackframe.h to arch-specific header directory. Make source
files and makefiles aware of the new header locations.
-Convert the include directory over to using bsdmake
syntax
-Update/add mkfiles
-Modify install(1) so that it can create symlinks
-Update makefiles to use new install(1) options
-Rename /usr/include/ibm to /usr/include/i386
-Create /usr/include/machine symlink to arch header files
-Move vm_i386.h to its new home in the /usr/include/i386
-Update source files to #include the header files at their
new homes.
-Add new gnu-includes target for building GCC headers
this change
- makes panic() variadic, doing full printf() formatting -
no more NO_NUM, and no more separate printf() statements
needed to print extra info (or something in hex) before panicing
- unifies panic() - same panic() name and usage for everyone -
vm, kernel and rest have different names/syntax currently
in order to implement their own luxuries, but no longer
- throws out the 1st argument, to make source less noisy.
the panic() in syslib retrieves the server name from the kernel
so it should be clear enough who is panicing; e.g.
panic("sigaction failed: %d", errno);
looks like:
at_wini(73130): panic: sigaction failed: 0
syslib:panic.c: stacktrace: 0x74dc 0x2025 0x100a
- throws out report() - printf() is more convenient and powerful
- harmonizes/fixes the use of panic() - there were a few places
that used printf-style formatting (didn't work) and newlines
(messes up the formatting) in panic()
- throws out a few per-server panic() functions
- cleans up a tie-in of tty with panic()
merging printf() and panic() statements to be done incrementally.
process waiting for" logic, which is duplicated a few times in the
kernel. (For a new feature for top.)
Introducing it and throwing out ESRCDIED and EDSTDIED (replaced by
EDEADSRCDST - so we don't have to care which part of the blocking is
failing in system.c) simplifies some code in the kernel and callers that
check for E{DEADSRCDST,ESRCDIED,EDSTDIED}, but don't care about the
difference, a fair bit, and more significantly doesn't duplicate the
'blocked-on' logic.
- Make the bootstrap /etc/mk be populated from the newly checked out source
- Don't chmod 755 all of /etc
- For the 'real' /etc/mk installing, let the /etc/mk ownership and permission
come from the mtree file, delete the contents of /etc/mk, then copy the .mk
files over and set reasonable permissions and ownership. (So that the .mk
get updated from the real usr/src/ copies, and no other junk if anything,
after the bootstrap phase, whatever happened there.)
