BAMBI Binutils

The gnu binutils package provides an assembler, a linker, and some assorted binary utilities. The programs that we are using are:

ece554-unknown-elf-as - assembler
ece554-unknown-elf-ld - linker
ece554-unknown-elf-nm - prints symbol table of object file
ece554-unknown-elf-objdump - disassembler, also dumps other object-file info

To port binutils to the Bambi architecture the following files were added to the standard binutils-2.9.1 directory:

bfd/cpu-ece554.c

This file simply contains a small structure that describes the Bambi architecture a little.

bfd/elf32-ece554.c

This file contains all of the code necessary to link several object files, it is used mainly by 'ld'

gas/config/tc-ece554.c

This is the assembler proper, it parses incoming opcodes and builds instructions from them.

gas/config/tc-ece554.h

I'm not sure if this is used..

include/elf/ece554.h

probably not used, or if it is, not needed

include/opcode/ece554.h

contains several structures used by the assembler to describe available instructions.

ld/emulparame/elf32_ece554.sh

Linker script template parameters, a few variables that are used when building the link scripts

ld/scripttempl/elf_ece554.sc

Linker script template, this is a shell script that outputs different linker scripts. Linker scripts tell the linker how to link several object files together into an executable.

opcodes/ece554-dis.c

The disassembler proper, takes binary instructions and looks up their names and parameters and prints them out nicely.

opcodes/ece554-opc.c

File that contains a structure with all of the possible instruction names, opcodes and parameters.

Assembly

Here's an example of some assembly, this is taken from start.s. It is the first piece of code executed when the machine boots up.


.global _start
_start:
	## disable all interrupts
	mtspr mr4, r0
	
	##  load _SDA_BASE_ to r13
	ori r13, r0, _SDA_BASE_@l
	lui r13, r13, _SDA_BASE_@h

	## setup system stack
	ori r1, r0, _stack_@l
	lui r1, r1, _stack_@h

	## jump to OS
	b _thumperos

Linking

The linker takes a list of .o files, which have been created by the assembler. Because the Assembler does not know where the code it is assembling will end up in the final output, it has to leave unknown fields blank, to be filled in when the final position is known. That final position is known at link time. The linker does a few main things:

group sections of the same type from different object files.
determine the final positions of all code.
"fixup" all of the fields which were unknown at assembly time.
output a final "executable" which contains a fully executable program.

The linker outputs code and data into a process image which are loaded directly into memory. For a layout of a process in memory, please see the ThumperOS section.

configuration

mkdir build.binutils
cd build.binutils
../binutils-2.9.1/configure --target=ece554-unknown-elf --prefix=/usr/home/tesch/ece554

Last modified: Sun Mar 11 00:56:44 CST 2001