1.13. PreBootLoader images (PBL)¶
Traditionally barebox generates a raw uncompressed binary. PBL is an effort to create self extracting compressed images instead. This helps on some boards where storage space is sparse. Another usecase of PBL is on SoCs on which the ROM code loads the initial bootloader to (limited) SRAM. With self extracting binaries, more binary space becomes available.
PBL is available for ARM and MIPS. It can be enabled in
make menuconfig with
[*] Pre-Bootloader image option.
The user visible difference is that with PBL support
barebox.bin is no longer
the final binary image, but instead
arch/$ARCH/pbl/zbarebox.bin. Use the
barebox-flash-image link which always points to the correct image.
1.13.1. Technical background¶
Normal object files are added to the make system using
obj-y += file.o.
With PBL the build system recurses into the source directories a second
time, this time all files specified with
pbl-y += file.o are compiled.
This way source code can be shared between regular barebox and PBL. A special
lwl-y += file.o which expands to
obj-y when PBL is disabled
pbl-y when PBL is enabled.
HINT: for getting an overview over the binaries, disassemble
barebox.bin with or without PBL support and also disassemble the PBL