When chaining COMBOOT images, the old images now get freed correctly.

Multi-level menus via COMBOOT rely on the COMBOOT program being able
to exit and invoke a new COMBOOT program (the next menu).  This works,
but rapidly (within about five iterations) runs out of space in gPXE's
internal stack, since each new image is executed in a new function
context.

Fix by allowing tail recursion between images; an image can now
specify a replacement image for itself, and image_exec() will perform
the necessary tail recursion.

This patch extends the embedded image feature to allow multiple
embedded images instead of just one.

gPXE now always boots the first embedded image on startup instead of
doing the hardcoded DHCP boot (aka autoboot).

Based heavily upon a patch by Stefan Hajnoczi <stefanha@gmail.com>.

The documentation in xfer.h and xfer.c does not say that the metadata
parameter is optional in calls such as xfer_deliver_iob_meta() and the
deliver_iob() method.  However, some code in net/ is prepared to
accept a NULL pointer, and xfer_deliver_as_iob() passes a NULL pointer
directly to the deliver_iob() method.

Fix this mess of conflicting assumptions by making everything assume
that the metadata parameter is mandatory, and fixing
xfer_deliver_as_iob() to pass in a dummy metadata structure (as is
already done in xfer_deliver_iob()).

fetchf_uristring() was failing to handle error values from
fetch_setting(), resulting in its attempting to allocate extremely
large temporary buffers on the stack (and so overrunning the stack and
locking up the machine).

Problem reported by Shao Miller <Shao.Miller@yrdsb.edu.on.ca>.

Automatically unregister any settings with the same name (and position
within the settings tree) as a newly registered settings block.

This functionality is generalised out from dhcp.c.

F8 is represented by the ANSI escape sequence "^[[19~", which is not
representable as a KEY_xxx constant using the current encoding scheme.
Adapt the encoding scheme to allow F8 to be represented, since PXE
requires that we may need to prompt the user to press F8.

Some devices take a very long time to initialise.  This can make it
difficult to visually distinguish between the error cases of failing
to start executing C code and failing to initialise a device.

Add a "gPXE initialising devices..." message.  The trailing ellipsis
indicates to the user that this may take some time, and the presence
of the message indicates to the developer that relocation etc. all
succeeded.

This brings us in to line with Linux definitions, and also simplifies
adding x86_64 support since both platforms have 2-byte shorts, 4-byte
ints and 8-byte long longs.

__cdecl is a misleading name, since it currently encapsulates both
cdecl and regparm(0) attributes.  Rename to __asmcall.

This fixes a regression introduced in commit 612f4e7:

  [settings] Avoid returning uninitialised data on error in fetch_xxx_setting()

in which the memset() was moved from fetch_string_setting() to
fetch_setting(), in order that it would be useful for non-string
setting types.  However, this neglects to take into account the fact
that fetch_string_setting() shrinks its buffer by one byte (to allow
for the NUL) before calling fetch_setting().

Restore the memset() in fetch_string_setting(), so that the
terminating NUL is guaranteed to actually be a NUL.

Some hardware vendors have been known to remove all gPXE-related
branding from ROMs that they build.  While this is not prohibited by
the GPL, it is a little impolite.

Add a facility for adding branding messages via two #defines
(PRODUCT_NAME and PRODUCT_SHORT_NAME) in config/general.h.  This
should accommodate all known OEM-mandated branding requirements.
Vendors with branding requirements that cannot be satisfied by using
PRODUCT_NAME and/or PRODUCT_SHORT_NAME should contact us so that we
can extended this facility as necessary.

Settings can be constructed using a dotted-decimal notation, to allow
for access to unnamed settings.  The default interpretation is as a
DHCP option number (with encapsulated options represented as
"<encapsulating option>.<encapsulated option>".

In several contexts (e.g. SMBIOS, Phantom CLP), it is useful to
interpret the dotted-decimal notation as referring to non-DHCP
options.  In this case, it becomes necessary for these contexts to
ignore standard DHCP options, otherwise we end up trying to, for
example, retrieve the boot filename from SMBIOS.

Allow settings blocks to specify a "tag magic".  When dotted-decimal
notation is used to construct a setting, the tag magic value of the
originating settings block will be ORed in to the tag number.
Store/fetch methods can then check for the magic number before
interpreting arbitrarily-numbered settings.

A DOS-style full path name such as "C:\Program Files\tftpboot\nbp.0"
satisfies the syntax requirements for a URI with a scheme of "C" and
an opaque portion of "\Program Files\tftpboot\nbp.0".

Add a check in parse_uri() to ignore schemes that are apparently only
a single character long; this avoids interpreting DOS-style paths in
this way, and shouldn't affect any practical URI scheme.

Callers (e.g. usr/autoboot.c) may not check the return values from
fetch_xxx_setting(), assuming that in error cases the returned setting
value will be "empty" (for some sensible value of "empty").

In particular, if the DHCP server did not specify a next-server
address, this would result in gPXE using uninitialised data for the
TFTP server IP address.

We have EFI APIs for CPU I/O, PCI I/O, timers, console I/O, user
access and user memory allocation.

EFI executables are created using the vanilla GNU toolchain, with the
EXE header handcrafted in assembly and relocations generated by a
custom efilink utility.

monojob_wait() was holding a reference to the completed job, meaning that
various objects would not be freed until the next job was plugged in to
the monojob interface.

The EFI timer runs at one tick per second, so using ">" rather than ">="
results in a two-second gap between dots.

We now have two implementations for the timer API: one using the
time-of-day counter at 40:70 and one using RDTSC.  Both make use of
timer2_udelay().

This allows settings to be expanded in a way that is safe to include
within a URI string, such as

  kernel http://10.0.0.1/boot.php?mf=${manufacturer:uristring}

where the ${manufacturer} setting may contain characters that are not
permitted (or have reserved purposes) within a URI.

Since whitespace characters will be URI-encoded (e.g. "%20" for a
space character), this also works around the problem that spaces
within an expanded setting would cause the shell to split command-line
arguments incorrectly.

fetch_string_setting() was subtracting one from the length of the
to-be-NUL-terminated buffer in order to obtain the length of the
unterminated buffer to be passed to fetch_setting().  This works
extremely well unless the length of the to-be-NUL-terminated buffer is
zero, at which point we end up giving fetch_setting() a buffer of
length -1UL, thereby inviting it to overwrite as much memory as it
wants...

Allow initiator to verify target authentication using CHAP.

Allow settings to be expanded in arbitrary commands, such as

  kernel http://10.0.0.1/boot.php?uuid=${uuid}

Also add the "echo" command, as being the easiest way to test this
features.

Print one dot per second while waiting in monojob.c (e.g. for DHCP,
for file downloads, etc.), to inform user that the system has not
locked up.

Patch contributed by Andrew Schran <aschran@google.com>, minor
modification by me.

Add yet another ugly hack to iscsiboot.c, this time to allow the user to
inhibit the shutdown/removal of the iSCSI INT13 device (and the network
devices, since they are required for the iSCSI device to function).

On the plus side, the fact that shutdown() now takes flags to
differentiate between shutdown-for-exit and shutdown-for-boot means that
another ugly hack (to allow returning via the PXE stack on BIOSes that
have broken INT 18 calls) will be easier.

I feel dirty.

Clearing the LOADED flag actually prevents users from doing clever things
such as loading an image, then loading a patch image, then executing the
first image.  (image_exec() checks for IMAGE_LOADED, so this sequence of
operations will fail if the LOADED flag gets cleared.)

This reverts commit 14c080020f.

Loading an image may overwrite part or all of any previously-loaded
images, so we should clear the LOADED flag for all images prior to
attempting to load a new image.

This commit implements GDB over UDP.  Using UDP is more complex than
serial and has required some restructuring.

The GDB stub is now built using one or both of GDBSERIAL and GDBUDP
config.h options.

To enter the debugger, execute the gPXE shell command:
gdbstub <transport> [<options>...]

Where <transport> is "serial" or "udp".  For "udp", the name of a
configured network device is required:
gdbstub udp net0

The GDB stub listens on UDP port 43770 by default.

This commit also includes a test to ensure that single stepping works,
since continue, kill, detach, and single step all share code.

Avoid calling cpu_nap() until after we have determined that there is
no input ready to read.  This avoids delaying for one timer interrupt
(~50ms) in the case of

  if ( iskey() )
     char = getkey()

which happens to be present in monojob.c, which is where we spend most
of our time looping (e.g. during any download).

This should eliminate the irritating tendency of gPXE to lose
keypresses.

Discovered on a Dell system where the serial port seems to send in a
constant stream of 0xff characters; this wouldn't be a problem in
itself except that each one triggers the 50ms delay (as mentioned
above), which really kills performance.