The option ROM header contains a one-byte field indicating the number
of 512-byte sectors in the ROM image.  Currently it is linked to
contain the number of uncompressed sectors, with an instruction to the
compressor to correct it.  This causes link failure when the
uncompressed size of the ROM image is over 128k.

Fix by replacing the SUBx compressor fixup with an ADDx fixup that
adds the total compressed output length, scaled as requested, to an
addend stored in the field where the final length value will be
placed.  This is similar to the behavior of ELF relocations, and
ensures that an overflow error will not be generated unless the
compressed size is still too large for the field.

This also allows us to do away with the _filesz_pgh and _filesz_sect
calculations exported by the linker script.

Output tested bitwise identical to the old SUBx mechanism on hd, dsk,
lkrn, and rom prefixes, on both 32-bit and 64-bit processors.

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

Commit b149a99 ([build] Round up SUBx deltas) introduced a
signed/unsigned issue that affects gPXE images built on 32-bit hosts.
The zbin fixup utility performed an unsigned division, which led to
.usb images with an incorrect number of sectors to load.

The issue snuck by on 64-bit hosts since uint32_t is promoted to long.
On 32-bit hosts it is promoted to unsigned long.

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

The zbin compressor fixup utility rounds down file sizes before
calculating their difference.  This produces incorrect values and may
cause truncated gPXE images to be loaded at boot.

The following example explains the problem:
ilen    = 48 bytes     (uncompressed input file)
olen    = 17 bytes     (compressed output file)
divisor = 16 bytes     (paragraph granularity)
fixmeup = 3 paragraphs (value to fix up)

olen / divisor - ilen / divisor
= 1 - 3
= -2 paragraphs  (old delta calculation)

( align ( olen, divisor ) - align ( ilen, divisor ) ) / divisor
= 2 - 3
= -1 paragraphs  (new delta calculation)

If we perform the SUBx operation with old delta:
fixmeup + -2 = 1 paragraph gets loaded by the prefix

With the new delta:
fixmeup + -1 = 2 paragraphs get loaded by the prefix

The old delta calculation removes the last paragraph; the prefix will
load a truncated copy of gPXE into memory.  We need to load 2
paragraphs since olen is 17 bytes.  Loading only 1 paragraph (16
bytes) would truncate the last byte.

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

Must check that argument to a fclose() is not NULL -- we can get to the
'err' label when file was not opened.  fclose(NULL) is known to produce
core dump on some platforms and we don't want zbin to fail so loudly.

Signed-off-by: Eygene Ryabinkin <rea-fbsd@codelabs.ru>