[syslinux] efi config hang

[Carl Karsten]

works with legacy, hangs with efi.

where works is:
No DEFAULT or UI configuration directive found!
but enter and ^v make things happen

hangs is: nothing happens, no response from keyboard, have to reboot.

note:
config prompt.cfg
prompt.cfg does not exist, but I would expect similar behaviour
between efi and legacy.

test is:
starting with blank image, mkfs, mount it...

+ cp /usr/lib/SYSLINUX.EFI/efi64/syslinux.efi target/EFI/BOOT/BOOTX64.EFI
+ cp /usr/lib/syslinux/modules/efi64/ldlinux.e64 target/EFI/BOOT/LDLINUX.E64
+ cp /usr/lib/syslinux/modules/efi64/vesamenu.c32
/usr/lib/syslinux/modules/efi64/libcom32.c32
/usr/lib/syslinux/modules/efi64/libutil.c32
target/EFI/BOOT/SYSLINUX/EFI64

+ cp /usr/lib/syslinux/modules/bios/vesamenu.c32
/usr/lib/syslinux/modules/bios/libcom32.c32
/usr/lib/syslinux/modules/bios/libutil.c32 target/boot/syslinux/
+ sudo extlinux --install target/boot/syslinux/
target/boot/syslinux/ is device /dev/loop0

target
├── boot
│   └── syslinux
│       ├── ldlinux.c32
│       ├── ldlinux.sys
│       ├── libcom32.c32
│       ├── libutil.c32
│       ├── syslinux.cfg
│       └── vesamenu.c32
└── EFI
    └── BOOT
        ├── BOOTX64.EFI
        ├── LDLINUX.E64
        ├── SYSLINUX
        │   └── EFI64
        │       ├── libcom32.c32
        │       ├── libutil.c32
        │       └── vesamenu.c32
        └── SYSLX64.CFG


# EFI/BOOT/SYSLX64.CFG
PATH /EFI/BOOT/SYSLINUX/EFI64/
default vesamenu.c32
label help
    menu label ^Help
    config prompt.cfg

# /boot/syslinux/syslinux.cfg
PATH /boot/syslinux/
default vesamenu.c32

label help
    menu label ^Help
    config prompt.cfg

https://salsa.debian.org/carlfk-guest/syslinux/blob/15fc479eb7ca5ab252ff6ff1fc94eb98d1ec31c9/tests/build_uefi_help.sh

--
Carl K