physical memory is sized by a loop that writes data to the first
word in a page, (writes something else to settle the bus) and then reads
back the word it wrote. If the read succeeds, the amount of physical
memory is increased by one page.
This fails on a 5000/1xx with a memory subsystem filled with 8 low-density
(4Mbyte) SIMMs. The memory-decoding hardware aliases the 32Mbytes of
physical memory at physical addresses 0, and at 32M (and presumably
at 64 and 96Mbytes.) The contiguous aliasing causes the memory-sizing
loop to continue at 32 MBytes, testing the memory that's really
at address 0, overwriting and crashing the kernel.
Fixed (for 1.2) by reading the SIMM-decoder stride size from the
motherboard, and reducing the loop bound to 32Mbytes on a 5000/1xx
with low-density SIMMs. (Other models have a non-power-of-2 maximum
memory and so are not subject to _contigous_ aliasing of physical memory).
never forwarded to me :-(.
> Clean up the FP stack before returning. The i387 exp() leaked an FP
> register on its first call. Subsequent calls reused the register so
> the leak didn't accumulate.
This takes care of two related problems:
- `umount -f' wouldn't work if someone's working directory is
the filesystem root.
- vfs_unmountall() would complain about a busy `/' on a
diskless setup.
The physical memory-sizer claims to preserve memory contents
(specifically the contents of msgbuf). The loop writes different
values into two adjacent locations and reads the contents of the
first, to ensure that whatever is read back from the first location is
from memory and isn't just the first write persisting on the bus.
The loop preserved the value of the first location, but not the second,
resulting in the second test value ('ZZZZ') over-writing a word in msgbuf.
- A fixed extent map (statically allocated descriptor storage) is
created in init386(), just before the call to consinit(). The
fixed descriptor storage has enough room for 8 region entires,
which is plenty for early initialization, but doesn't chew up
that much memory.
This extent map (ioport_ex) manages the i386 i/o port
space (0x0 - 0xffff).
- Just before the call to configure() in cpu_startup(), a
flag is set which notifies the bus_io functions that it is
safe to use malloc() to allocate descriptor storage, in the
event that more than 8 regions are needed.
- bus_io_map() attempts to allocate the specified region from
ioport_ex. If the allocation succeeds, the io handle is
filled in. If the allocation fails, it is implied that
something else is already using that io space, and an
error condition is returned.
- bus_io_unmap() frees a region previously allocated from
ioport_ex in bus_io_map(). If the free fails, a warning
is printed on the conole.
These changes implement "port accounting". This is required for
proper autoconfiguration on the i386 port, and makes dealing with,
among other things, PCMCIA io mappings _much_ easier.
dump is present. This was caused by the fact that kvm_dump_mkheader() was
called *before* savecore checks the dump magic and kvm_dump_mkheader() returned
-1 without setting an error message. The latter is fixed now.
Understands allocation aligment and boundary restrictions, "specific region"
allocations, and suballocations. Capable of statically or dynamically
allocating map overhead.
Many thanks to Matthias Drochner for running the code for me, and sending
me bug fixes, optimizations, and suggestions. Also, many thanks to
Chris Demetriou for his extremely helpful suggestions.
XXX No manual page yet. One is forthcoming, as soon as I can scare up
the time to write one. This has been sitting on my plate for quite a
while, and several projects are waiting for it. Time to move on.
