Got a question for the bootloader/flash gurus

Hi bkucera & Jesse,

> > So how does the .bss section get allocated in memory if the sections that refer to

> > it in the ELF file don't make it into the .flash file?

The linker groups all .bss input sections into the .bss output section and assigns

addresses to the symbols that end up in the .bss output section. So, the linker

allocates the memory -- or maybe better -- the linker reserves/assigns the

address range occupied by .bss (as well as the other sections).

Your executable code (.text) and sometimes your initialized data (.data -- e.g. a

pointer to a buffer in .bss that has an initializer such as: unsigned char *p = mybuf)

refer to .bss -- and sections that contain initialized data make it into the flash

file (the LOAD attribute is set). After initialization, accessing data in .bss is the

same as accessing data in any other section (ignoring .sbss and .sdata).

So the only practical difference between .data and .bss is: .data is initialized by

copying an image into the memory and .bss is initialized by clearing the memory.

> I think the .elf just leaves this... blank. Again, crt0 has to know where the bss

> is to initialize it.

Correct. Take a look at objdump output. The size of the .bss elf file section

is zero. crt0 knows the start and end address of .bss based on the symbols

__bss_start and __bss_end which are provided by the linker. You can find these

symbols in the linker command file (generated.x) -- which is in the

system_description directory in your syslib build tree.

Regards,

--Scott