If you’re running FreeBSD on an AM5 board with a recent BIOS update and your system freezes during boot — right after the EFI framebuffer line — you’re probably hitting a firmware bug in AGESA 1.3.0.0a.

The Problem

After updating my Gigabyte B650 GAMING X AX V2 to BIOS F41a (AGESA 1.3.0.0a, released March 2026), FreeBSD stopped booting entirely. All versions — 14.2, 14.4, and 16.0-CURRENT — freeze hard after printing EFI framebuffer information. No panic, no output, complete CPU lockup (caps lock LED goes dead). The same issue has been reported on ASRock X870 boards with Ryzen 9600X on the FreeBSD forums.

Investigation

I built a diagnostic FreeBSD loader with printf calls at every stage of the EFI boot handoff. The results were clear: the hang occurs inside the UEFI firmware’s ExitBootServices() call. The loader calls into firmware, and firmware never returns.

An interesting secondary finding: adding printf (which calls the UEFI OutputString boot service) between GetMemoryMap and ExitBootServices invalidates the memory map key. The firmware then hangs on the stale key instead of returning an error — which is itself a firmware bug. Well-behaved firmware should return EFI_INVALID_PARAMETER and let the caller retry.

Attempted Loader Fix

Knowing that stale memory map keys were part of the picture, I wrote a patch for the FreeBSD EFI loader (stand/efi/loader/bootinfo.c) that:

1. Pre-allocates the memory map buffer with slack before the retry loop — no more AllocatePages inside the loop
2. Disables the UEFI watchdog timer before calling ExitBootServices
3. Keeps the retry loop tight — only GetMemoryMap followed immediately by ExitBootServices, with zero intervening boot service calls

This matches the strategy used by the Linux EFI stub, which has had these hardening measures for years.

Unfortunately, the patched loader still hangs on BIOS F41a. The firmware bug in AGESA 1.3.0.0a is not just about stale keys — ExitBootServices is fundamentally broken, even with a fresh memory map key.

The Fix: Downgrade Your BIOS

The only workaround is to downgrade your BIOS. I flashed back to F37 (AGESA 1.2.0.3g) using Q-Flash, and FreeBSD boots perfectly again. Here’s the full test matrix:

FreeBSD Version	Loader	BIOS F37 (AGESA 1.2.0.3g)	BIOS F41a (AGESA 1.3.0.0a)
14.4-RELEASE	Stock	Boots	Hangs
16.0-CURRENT	Stock	Boots	Hangs
16.0-CURRENT	Patched	Boots	Hangs

I avoided BIOS versions F38–F40 (AGESA 1.2.8.0) as there are reports of boot failures on some AM5 boards with that AGESA version as well.

Affected Hardware

• My system: Gigabyte B650 GAMING X AX V2, Ryzen 9 9900X
• Also reported: ASRock X870 + Ryzen 9600X (FreeBSD Forums)
• Likely affected: Any AM5 board shipping AGESA 1.3.0.0a

Next Steps

The loader hardening patch didn’t fix the AGESA bug, but it’s still valid as defensive improvement — it eliminates a class of firmware interaction bugs by keeping the ExitBootServices retry loop free of boot service calls. I’ll be submitting it upstream to FreeBSD as a hardening measure.

If you’re hitting this issue: downgrade your BIOS to any version before AGESA 1.3.0.0a. For Gigabyte B650 boards, F37 is a safe choice.