Some BIOSes are reported to corrupt %ebx when using INT 15,2401 (see
http://opensolaris.org/jive/thread.jspa?messageID=377026).  Guard
against this by preserving all (non-segment) registers.

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

The symbol_text16 is defined globally by the linker.  Use rm_text16
instead of _text16 for the local variable within librm.S to avoid
confusion when reading linker maps.

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

libflat no longer has anything to do with flat real mode; it handles
only the A20 gate.  Update library name to match.

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

Flat real mode will have been set up as a side-effect of the
protected-mode call invoked during install_block() for .text16.early;
there is no need to do so explicitly.

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

Use the real-mode address ffff:0010 to access the linear address
0x100000, and so test whether or not the A20 gate is enabled without
requiring a switch into flat real mode (or some other addressing
mode).

This speeds up CPU mode transitions, and also avoids breaking the NBP
from IBM's Tivoli Provisioning Manager for Operating System
Deployment.  This NBP makes some calls to iPXE in VM86 mode rather
than true real mode and does not correctly emulate our transition into
flat real mode.

Interestingly, Tivoli's VMM *does* allow us to switch into protected
mode (though it patches our GDT so that we execute in ring 1 rather
than ring 0).  However, paging is still disabled and we have a 4GB
segment limit.  Being in ring 1 does not, therefore, restrict us in
any meaningful way; this has been verified by deliberately writing
garbage over Tivoli's own GDT (at address 0x02201010) during a
nominally VM86-mode PXE API call.  It's unclear precisely what
protection this VMM is supposed to be offering.

Suggested-by: Joshua Oreman <oremanj@rwcr.net>
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>

iPXE currently insists on residing in an even megabyte.  This imposes
undesirably severe constraints upon our PMM allocation strategy, and
limits our options for mechanisms to access ROMs greater than 64kB in
size.

Add A20 handling code to libflat so that prefixes are able to access
memory even in odd megabytes.

The algorithms and tuning parameters in the new A20 handling code are
based upon a mixture of the existing iPXE A20 code and the A20 code
from the 2.6.32 Linux kernel.

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

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

When returning to real mode, set 4GB segment limits instead of 64kB
limits.  This change improves our chances of successfully returning to
a PMM-capable BIOS aftering entering iPXE during POST; the BIOS will
have set up flat real mode before calling our initialisation point,
and may be disconcerted if we then return in genuine real mode.

This change is unlikely to break anything, since any code that might
potentially access beyond 64kB must use addr32 prefixes to do so; if
this is the case then it is almost certainly code written to expect
flat real mode anyway.

Note that it is not possible to restore the real-mode segment limits
to their original values, since it is not possible to know which
protected-mode segment descriptor was originally used to initialise
the limit portion of the segment register.

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.

Try to avoid future problems caused by implicit section flags and/or
type information by instituting a policy that all .section
declarations must explicitly state the flags and type.

Most of this change was achieved using

    perl -pi \
      -e 's/".text"$/".text", "ax", \@progbits/ ; ' \
      -e 's/".text16"$/".text16", "ax", \@progbits/ ; ' \
      -e 's/".text16.null"$/".text16.null", "ax", \@progbits/ ; ' \
      -e 's/".text16.data"$/".text16.data", "aw", \@progbits/ ; ' \
      -e 's/".data"$/".data", "aw", \@progbits/ ; ' \
      -e 's/".data16"$/".data16", "aw", \@progbits/ ; ' \
      -e 's/".bss"$/".bss", "aw", \@nobits/ ; ' \
      -e 's/".bss16"$/".bss16", "aw", \@nobits/ ; ' \
      -e 's/".prefix"$/".prefix", "ax", \@progbits/ ; ' \
      -e 's/".prefix.lib"$/".prefix.lib", "awx", \@progbits/ ; ' \
      -e 's/".prefix.data"$/".prefix.data", "aw", \@progbits/ ; ' \
      -e 's/".weak"$/".weak", "a", \@nobits/ ; ' \
      `git grep -l '\.section'`

With a 16-bit operand, lgdt/lidt will load only a 24-bit base address,
ignoring the high-order bits.  This meant that we could fail to fully
restore the GDT across a call into gPXE, if the GDT happened to be
located above the 16MB mark.

Not all of our lgdt/lidt instructions require a data32 prefix (for
example, reloading the real-mode IDT can never require a 32-bit base
address), but by adding them everywhere we will hopefully not forget
the necessary ones in future.

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().

See http://etherboot.org/wiki/dev/gdbstub for documentation.

confusing to read the code.

stack; it breaks vmxassist.

outside of librm.S.

real_call(), rather than moving it to the RM stack and back again.
This allows the real-mode function to completely destroy the stack
contents, provided that it manages to return to real_call().

call.

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

worrying about its stack being destroyed during the Etherboot run.

install() now calls relocate(), moves the protected-mode code to the new
location, and calls hide_etherboot().

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

Add __from_{text16,data16}.

between the low half stored in the static variable rm_sp, and the high
half stored on the prot_call() stack, because:

  Just using the stack would screw up when a prot_call()ed routine
  executes a real_call(); it would have no way to find the current top of
  the RM stack.

  Extending rm_sp to rm_esp would not be safe, because the guarantee that
  rm_sp must return to the correct value by the time an external
  real-mode call returns applies only to %sp, not to %esp.

from protected-mode code.

Set up %ds to point to .data16 in prot_to_real, so that code specified
via REAL_EXEC() and friends can access variables in .data16.

Move most real-mode librm variables from .text16 to .data16.

install_prealloc.  I *think* these will suffice for all the 16-bit
prefixes.

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

Doing so, in fact, seems to expose an assembler bug; (a-b-0) is
apparently not the same as (a-b).  Go figure.

initialise_via_librm.

call it initialise() and place it in main.c.  :)

of librm.

always saves 32 bits).