[syslinux] "EDD Load error" on btrfs, how to debug?

[Ady]

> Size problem again?
 
This problem is not exactly about the (apparent but not factual) 
available size to install Syslinux on Btrfs.

The bug reports (in bugzilla.syslinux.org, in this Syslinux Mailing 
List, in bbs.archlinux.org , in bugs.archlinux.org and in other 
places) are clearly showing different kinds of error messages and 
different Syslinux versions (including 4.xx).

To be clear, the (apparent but not factual) 64KB size issue in Btrfs 
triggered by Syslinux 6.xx *might* be related to these cases, but the 
reports include cases where:

_ users going back to (or simply trying) Syslinux 4.xx are still 
seeing the same error.

_ users using some Syslinux 6.xx version are booting fine and the 
error is seen only after some (even minor) update.

Since the same error message can be seen under all sorts of Syslinux 
versions and circumstances other than the 64KB problem (which is not 
even an issue in Syslinux 4.xx), the conclusion is that only part of 
the reports and only part of the symptoms might be related to the 
size limitation; while some reports and some symptoms are not related 
to the size issue nor to Btrfs.

Moreover, similar error messages could be seen in situations where 
Btrfs is not even used for the Syslinux boot volume, which adds to 
the confusion about the source of the problem.

It should be noted that some users are (at least seemingly) capable 
of successfully installing Syslinux 6.02 on Btrfs (even with the 64KB 
problem), whereas some users are failing to install Syslinux 4.xx in 
a Btrfs volume. Therefore, other than the 64KB issue in Syslinux 
6.xx, there is probably something else interfering (in addition to 
the 64KB issue). Whether this "something else" is related to some 
Btrfs feature, or to some Btrfs limitation, or to some (Btrfs-tools) 
package version, or to how exactly the specific version of Syslinux 
was installed, or to... I (we) don't know (yet).

In any case, hopefully Syslinux (in the future) should be capable of 
overcoming the 64KB issue. ETA: unknown/undefined.

Regards,
Ady.