FIFA International Soccer (DOS) – AMD K6 start-up fix

A tiny patcher that lets FIFA International Soccer (EA Sports, DOS, 1993/94) start on AMD K6 processors.

It changes 7 bytes in the start-up loader of your own FIFA.EXE. It contains no game code, no game data and does not ship the game. You need a legally obtained copy of the game.

Abnormal program termination: Memory protection fault
CS:EIP = 000Fh:0009C4E8h

That message right after typing FIFA (the address differs, e.g. 000Fh:000A0697h or 000Fh:000AC0D8h, depending on the memory setup) is what this fixes. Lowering the multiplier, disabling the L1/L2 caches or slowing the CPU down does not help, because the cause is not speed. It is a CPU-dependent value in the game's start-up loader (details in docs/TECHNICAL.md).

Quick start

Make a copy of your game folder first (the tool also makes a backup, but be careful anyway). Then pick one way:

A. On the DOS machine: FK6FIX.EXE

Download FK6FIX.EXE from the Releases page. It is a small 16-bit DOS program (no DOS extender, no memory manager) that the workflow in this repository builds from c/fk6fix.c and tests in DOSBox; its SHA-256 is listed next to it. Copy it next to the game and run:

FK6FIX FIFA.EXE

The original is kept as FIFA.ORG. Then start the game as usual.

Command	Effect
FK6FIX --check FIFA.EXE	Only report whether the file needs the fix. Changes nothing.
FK6FIX -o FIFAK6.EXE FIFA.EXE	Write a patched copy and leave the original untouched.
FK6FIX --no-backup FIFA.EXE	Patch in place without creating FIFA.ORG.

B. On a modern computer: Python

Install Python 3 (3.8 or newer, Windows / macOS / Linux), then run:

python fifa_k6_fix.py "path/to/FIFA.EXE"

The original is kept as FIFA.EXE.orig. Same options as above (--check, -o FILE, --no-backup). Copy the patched game folder to your DOS machine afterwards. The Python version also prints the SHA-256 of the file.

C. Build FK6FIX.EXE yourself

• Open Watcom, 16-bit DOS target (what the workflow uses): wcl -zq -bt=dos -ms -os -fe=FK6FIX.EXE c/fk6fix.c
• any modern system: cc -std=c89 -O2 -o fk6fix c/fk6fix.c

The source is plain C89 and reads the file in small blocks, so other DOS compilers should work too; only Open Watcom is used and tested by the author.

D. By hand (hex editor)

Search for these two byte patterns in FIFA.EXE (?? = any byte, each must occur exactly once):

#	Search for	Change
A	89 0D ?? ?? ?? 00 05 A5 A5 A5 A5 E8	replace the first six bytes 89 0D ?? ?? ?? 00 with 90 90 90 90 90 90
B	0F A2 80 E4 0F 80 FC 04 74 10 8B 44 24 1C	replace the 74 (9th byte) with EB

For the standard build listed below this is offset 0x96F43 (A) and 0x96EAA (B).

Things to know

• Keep the file name FIFA.EXE. The start-up loader looks for its own EXE by that hard-coded name in the current directory, so a renamed copy will most likely not start.
• The tool refuses to touch anything it does not recognise: wrong file, ambiguous matches, or a file that was already modified by something else. Running it twice is harmless ("Both patch sites already carry the fix").

Known builds

The patcher recognises these builds (all of them were checked with --check; the loader is the same code block in each, the two patch sites are always 0x99 bytes apart):

Build	Size	SHA-256	Patch sites (file offset A / B)	Status
Floppy release (1994)	816,980	8f1ae8d4080729df06a8ec4d2fceee820f21b21325b7146f183cc50d06a48971	0x96F43 / 0x96EAA	tested on real K6-III+ hardware and in DOSBox-X
CD-ROM release ("Special Edition")	856,244	00956baf8ef9d1cffde9e5e0d85ddc3b9a2e2dff61711523321443cadf545d3c	0xA08AF / 0xA0816	tested on real K6-III+ hardware (needs the CD and a working DOS CD driver, see Troubleshooting)
Patched "4 MB" EXE for the CD-ROM release	835,860	30e405ba6e9195bdea6fcfb7316424b3ce15d1c2f405465c14134f8a5aaaf774	0x9B907 / 0x9B86E	tested on real K6-III+ hardware (needs the CD and a working DOS CD driver, see Troubleshooting)
EDITOR.EXE of the CD-ROM release (team editor)	313,780	d07bff908524c0d00ec485c53caa6a7301a6c617ff72a92c58360c79e535e0ff	0x1C1AD / 0x1C114	tested on real K6-III+ hardware

CRC-32 of the unpatched files (as printed by FK6FIX.EXE): floppy 2D5602DB, CD-ROM 5E0BCA79, "4 MB" A5ADB291, EDITOR.EXE F73CEBB5.

For the standard build, CRC-32 is 2D5602DB before and 4A08FA59 after patching (FK6FIX.EXE prints CRC-32, the Python tool prints both); SHA-256 after patching is ecdecd544ac0d0ad4e677a6269f671980de1759c2b42745820b9b4bdeeff7395.

The patcher finds its targets by byte pattern, not by fixed offset, so it also works on other builds of the game as long as their loader is built the same way. If you have another version (other languages, other releases, ...), run --check on it:

• "file needs the fix" or "already carry the fix": it works, please report the size, SHA-256 and the result so the table can be extended. Reports from real hardware (does the patched file start?) are the most valuable ones.
• "loader signature was not found": that build differs. Please report its size and SHA-256 (never upload the game itself).

The tool also prints the file name the loader looks for (see "Keep the file name" above); run --check once on your copy to see it.

Tested on

• Real hardware: AMD K6-III+ on an Asus P5A (Super Socket 7), MS-DOS. Before: crash as above. After: the game starts and runs (floppy build, CD-ROM build and "4 MB" build; the latter two with the CD inserted).
• DOSBox-X: the patched file runs.
• FK6FIX.EXE itself: built and tested automatically in DOSBox against synthetic files (including files larger than 64 KB) on every change. On real DOS hardware (K6 machine) --check was run on all three known builds and reports the same offsets as the Python tool. Reports of patching runs from other DOS machines are welcome.

Reports from other CPUs are welcome. The patch should also be harmless on Intel/Cyrix/other CPUs, because it makes the loader use the same value as a 486 would on every CPU. A report in the VOGONS forum describes the same message on a Cyrix 486 upgrade; whether this patch fixes that has not been verified.

Troubleshooting (CD-ROM and "4 MB" builds)

The CD-ROM and "4 MB" builds read their game data from the CD (D:\FIFA\...). The loader patch only fixes the start-up crash; the following problems were seen on the test machine after patching and had other causes:

• "No CDROM drive detected": no CD driver / MSCDEX is loaded, or the CD is not inserted.
• Hard freeze right after starting the game (only a reset helps): seen with the original Windows MS-DOS MSCDEX together with VIDE-CDD. Using SHSUCDX (with the same VIDE-CDD driver) instead of MSCDEX fixed it. If DIR D: does not work in plain DOS, the game cannot work either; fix the CD driver first.
• "Insufficient free conventional memory" (CD-ROM build): seen with the original MSCDEX set-up even though about 620 KB of conventional memory were free. It disappeared after switching to SHSUCDX + VIDE-CDD. Disabling the sound card in FIFA.CFG also moved the game past this message once, so the exact cause (CD driver or sound set-up) is not settled; try the CD driver first.
• Stuttering in the CD-ROM and "4 MB" builds (the floppy build is smooth on the same machine): observed on the K6-III+ at full speed, with and without sound, with PIO and DMA CD access. It disappeared when the CPU was slowed down with a CPU throttle setting (the multiplier alone did not make the difference). The cause has not been found; it looks like a timing problem that appears on a very fast CPU. Reports from other CPUs are welcome.
• Missing in-game sound effects in the CD-ROM and "4 MB" builds (e.g. the referee's whistle at kick-off and the shot sounds; crowd chants and, in the CD build, the commentary are audible; the floppy build plays everything): seen with SB16 and plain Sound Blaster, with and without an FM music card. Copying SFX\*.VOC to the hard disk does not help, and the sample files are identical to the floppy build. This is not caused by the loader patch and it also happens in an emulator. Findings from disassembling the decrypted game code: these two builds only load the effect samples (SFX0–SFX15, FHORN.VOC) when the sound-effects card is type 12 (Gravis Ultrasound); the floppy build always loads them. With an FM music card the effects are played from the 202-byte SFX.XMI instead, and the code skips effects 11 and 12 (the kick-off whistle is effect 11). Removing the load condition alone does not bring the whistle back, so a second blocker exists. Because the game image is encrypted, a fix would need extra edits made by the loader after decryption; none exists. Workaround: use the patched floppy build if the effects matter more than the intro and commentary of the CD build.
• Replays: floppy-generation replays are 21,634 bytes, CD-generation replays 21,674 bytes. Keep each replay set with the build that created it (the mismatch is a suspected cause of a black screen when loading a replay, not confirmed).

What exactly does the patch change?

Short version: the loader computes a decryption key. One step depends on whether the CPU notices that an instruction was overwritten right before it executes (486: no; Pentium: yes) and the loader compensates by asking the CPU family via CPUID. The K6 reports "Pentium-class" but most likely does not behave like a Pentium in that one spot, so the compensation is applied wrongly, the key is wrong and the decrypted code is garbage. (This explanation fits every observation made so far, and the patch built on it works, but the K6 internals involved were not measured separately.) The patch removes the self-modifying store (site A) and disables the compensation (site B), so every CPU gets the key a 486 gets. Full explanation with the instruction listing: docs/TECHNICAL.md.

The patch does not remove or bypass any licence check, serial number, manual question or disc check, and it does not change the game itself.

Running the self-tests

python tests/test_patcher.py

The test builds synthetic files that contain only the short patterns and needs no game file. If a C compiler is installed, it also checks that the C version (the source of FK6FIX.EXE) produces the same output as the Python version, including a build with a 64-byte read buffer that forces the patterns across block borders. tests/dos_test.py plus .github/workflows/build.yml run the real DOS executable in DOSBox.

Undo

Copy the backup back over the game EXE: FIFA.ORG (DOS tool) or FIFA.EXE.orig (Python tool).

Disclaimer and licence

This is an independent compatibility tool. It is not affiliated with, endorsed by or sponsored by Electronic Arts, FIFA or AMD; all names and trademarks belong to their respective owners. The tool contains no part of the game except the two short byte patterns needed to locate the patch sites. You are responsible for using it only on a copy of the game you are entitled to use. It comes without any warranty; keep a backup.

The tool and its documentation are released into the public domain under The Unlicense.

Changelog

• 1.2: FK6FIX.EXE, a 16-bit DOS version of the tool (c/fk6fix.c, built and tested by the workflow); the Python tool prints CRC-32 as well. The IPS patch was removed: it only fit one build and could not check what it was applied to.
• 1.1: prints the file name the loader looks for; CD-ROM and "4 MB" builds added to the list of recognised builds.
• 1.0: first release.