[syslinux] Debug C32 Module

Ady Ady ady-sf at hotmail.com
Fri May 24 07:55:59 PDT 2019

> we have wrote a own C32 module, loaded with "DEFAULT mod.c32"
> But sometime the module mod.32 are not loaded & started.
> How we can debug this ?
> Or give some debug output.
> In the main of the module there is a printf, but the text are not shown
> at booting.
If you are building the binaries by yourself, then nobody really knows 
where the problem could be, considering that even the current git 
master head fails for UEFI mode.

If you are using some package from some distro, or perhaps upstream 
6.04-pre1, please include such details in the future.

Yours would not be the first report about display problems when using 
syslinux.efi. One such report (among others) is about lua.c32, also 
failing to correctly display output text; the "output" is there, but it 
cannot be seen/read.

Having said that, at least one test could be performed anyway, just in 

Instead of using:

DEFAULT mod.c32

please try:

DEFAULT modlabel

LABEL modlabel
COM32 mod.c32

The point is to use a label for the DEFAULT directive, instead of a 
non-label command.

With this minimal cfg file, When you boot you should at least get to 
the Syslinux "boot" prompt. At that point, press [ENTER] in order to 
execute the default label.

Probably the result won't change from your previous test, but at least 
you will be able to discard the potential problem in the DEFAULT 

Other than that, _perhaps_ the following might help someone with the 
relevant skills (although, please note that the whole page is rather 
outdated and possibly not very much relevant for UEFI, but YMMV):



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