Firmware Test Suite - ebda test
This test ensures that the Extended BIOS Data Area (EBDA) is marked as reserved in the memory map. For traditional BIOS firmware the memory map is via Int 0x15 AX=0xe820 and for UEFI this is via the UEFI memory map run time service. Normally the EBDA exists in the 2-4K section below the top of the low 640K memory region and contains firmware created dynamic data structures such as floating table pointers (e.g. for MultiProcessor tables) and possibly dynamically created ACPI tables. If the EBDA regions is not reserved in the memory map there is a risk that the kernel will overwrite this region - so the kernel works around this by reserving 4K at the end of the 640K region just in case (since old Dells seem to need 4K reserved (bugzilla 2990)).
Examples:
sudo fwts ebda -
..runs the ebda test on your machine and dumps the output to stdout.
Explanation of test results
Certain test results may require a little more explanation. This section will try and give some context to specific test failures.
Error ID |
Explanation |
EBDAMappedNotReserved |
The EBDA region is not reserved in the memory map. This can cause random system errors if critical system data is stored in the EBDA. Note the kernel has works around this by allocating the top 4K of the 640K region if the EBDA is not reserved. However, if the EBDA is reserved and is the *wrong* size (too small), then one may get random corruption issues. |