These files cannot be automatically relicensed by util/relicense.pl
since they either contain unusual but trivial contributions (such as
the addition of __nonnull function attributes), or contain lines
dating back to the initial git revision (and so require manual
knowledge of the code's origin).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

On an Intel CPU supporting VMX, KVM will emulate instructions while
the CPU state remains "invalid".  In real mode, the CPU state is
defined to be "invalid" if any segment register has a base which is
not equal to (sreg<<4) or a limit which is not equal to 64kB.

We don't actually use the base stored in the REAL_DS descriptor for
any significant purpose.  Change the base stored in this descriptor to
be equal to (REAL_DS<<4).  A segment register loaded with REAL_DS is
then automatically valid in both real and protected modes.  This
allows KVM to stop emulating instructions much sooner.

The only use of REAL_DS for memory accesses currently occurs in the
indirect ljmp within prot_to_real.  Change this to a direct ljmp,
storing rm_cs in .text16 as part of the ljmp instruction.  This
removes the only memory access via REAL_DS (thereby allowing for the
above descriptor base address hack), and also simplifies the ljmp
instruction (which will still have to be emulated).

Load the real-mode interrupt descriptor table register before
switching to real mode, since this avoids triggering an EXCEPTION_NMI
and corresponding VM exit.

This reduces the time taken by prot_to_real under KVM by around 65%.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

When running in a virtual machine, switching to real mode may be
expensive.  Allow interrupts to be enabled while in protected mode and
reflected down to the real-mode interrupt handlers.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Use the shared code in libflat to perform the A20 transitions
automatically on each transition from real to protected mode.  This
allows us to remove all explicit calls to gateA20_set().

The old warnings about avoiding automatically enabling A20 are
essentially redundant; they date back to the time when we would always
start hammering the keyboard controller without first checking to see
if gate A20 was already enabled (which it almost always is).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

The userptr_t is now the fundamental type that gets used for conversions.
For example, virt_to_phys() is implemented in terms of virt_to_user() and
user_to_phys().

__from_data16 and __from_text16 now take a pointer to a
.data16/.text16 variable, and return the real-mode offset within the
appropriate segment.  This matches the use case for every occurrence
of these macros, and prevents potential future bugs such as that fixed
in commit d51d80f.  (The bug arose essentially because "&pointer" is
still syntactically valid.)

outside of librm.S.

Add some of the missing parts to libkir.h.

link-time check for section overlaps.  (In order to avoid wasting
space in the executable image, .bss16 will overlap with the following
section, which is .text).

somewhat redundant, and also causes gas to complain when we include
the profiling code (which uses an i586 instruction).

userptr_add().

to the REAL_CODE interface.

Fix bug that caused over-allocation of .text16 and .data16 memory areas
by a factor of 16.

completely.

the only one we actually use).  This allows REAL_EXEC fragments to
contain proper references to constraints (e.g. "%w0"), rather than having
to force the use of specific registers.

Note that the "num_constraints" parameter is now completely obsolete, and
that we can probably reduce the syntax to something like
  __asm__ __volatile__ ( REAL_CODE ( "asm statements" )
                         : output constraints
                         : input constraints
                         : clobber );
which would look much more natural, and avoid the need to always specify
a clobber list.


Add userptr_t to libkir.h, to allow it to at least compile.

usual __{text,data}16 trick work with arrays.  gcc seems to accept the
__asm__ ( asmlabel ) only after the [] of the array declaration, not
before.

the kernel), which encapsulates the information needed to refer to an
external buffer.  Under normal operation, this can just be a void *
equivalent, but under -DKEEP_IT_REAL it would be a segoff_t equivalent.

Use this concept to avoid the need for bounce buffers in int13.c,
which reduces memory usage and opens up the possibility of using
multi-sector reads.

Extend the block-device API and the SCSI block device implementation
to support multi-sector reads.

Update iscsi.c to use user buffers.

Move the obsolete portions of realmode.h to old_realmode.h.

MS-DOS now boots an order of magnitude faster over iSCSI (~10 seconds
from power-up to C:> prompt in bochs).

Use .text16.data section with "aw" attributes, to avoid section type
conflicts when placing both code and data into .text16.

Add __from_{text16,data16}.

interrupt vectors, for example, will be easiest to handle if placed in
.text16.

.data16.  librm will need to supply "char *data16", i.e. the virtual
address of the start of .data16.

However, it's worth adding a .size directive so that objdump reports the
correct sizes for the code fragments.

advantage of the fact that we have to have a permanently-resident block
in base memory.