Recitation Material of
Engineering an Assembler
June 11, 2013
Main Purpose of HW3
• The main purpose of hw3 is to give a chance
implementing macro function and a linker.
• Code should be written in MIPS, and since it is
too complicate to implement in short time, we
have built a package to support ~~~
Task 1
• First, download and take a look at the fibonacci.f file. In order
to compile it, you need an external function called "fibo".
Therefore, you will implement this "fibo" function in a file
called "func-fibo.f". After you finish this work, you can
compile your code using following command line:
• gfortran-4.2 -o fibonacci fibonacci.f func-fibo.f
• you can use g77 to replace gfortran of course.
Fibonacci.f file
program main
integer Fn_1,Fn,n,val,fibo
read(*,*) n
Fn_1=0
Fn=1
val=0
if ( n .EQ. 0 ) then
val=0
elseif ( n .EQ. 1 ) then
val=1
elseif ( n .GE. 2 ) then
do 10 i=2, n
val=fibo( Fn_1, Fn)
Fn_1=Fn
Fn=val
10
continue
endif
write(*,*) val
stop
end
Task 2
• In task2, you assume yourself as John Backus. You just finished
implementing IBM's assembly language, and you knew in companies such
as Remington Rand, scientist like Grace Hopper already implemented
assembly languages, and they even developed some "higher-level"
language using primitive compiler like "A-0 System". What you need to do
is to summarize your experience developing assembly language, and
produce higher-level programming language called "Fortran".
The first step toward the goal, is to reuse some existing code. Because
writing code in assembly is hard and therefore reusing existing code must
be one of functionalities in this new language "Fortran". What you need to
do:
write a macro file called "macro-fibo.f” , and read the file into your new
compiler, translate it into assembly language and output compiled file in
MIPS assembly language format.
What is the macro file
• #define reduce( *1, *2 )
sub reduce, *1, *2
What we need to do: replace the variable name
and macro name with corresponding register
name in MIPS.
What is in package?
• You can use QtSpim to load "program-main.s" file. This
program
will
read
"fibonacci.f",
and
output
"second_mips_fortran.s" file.
• What you need to do is like what you have done in Task1,
add some code to make this fibonacci code works. If you
successfully add some code, this file can be compiled using
gfortran or g77. In the sense, you have included a
new functionality called "macroinstruction" for "Fortran"
language.
What is in second_mips_fortran.s ?
•
•
.globl main
main:
li $2, 5
syscall
add $7, $2, 0
li $5, 0
li $6, 1
li $8, 0
li $24, 0
bne $7, $24, elseif1
li $8, 0
j finish
elseif1:
li $24, 1
bne $7, $24, elseif2
li $8, 1
j finish
elseif2:
li $24, 2
blt $7, $24, elseif3
li $25, 2
begin:
beq $25, $7, endloop
add $8, $5, $6
add $5, $6, 0
add $6, $8, 0
add $25, $25, 1
j begin
endloop:
elseif3:
finish:
li $2, 1
add $4, $8, 0
syscall
nop
nop
nop
li $2, 10
syscall
Recall Fibonacci.f file
program main
integer Fn_1,Fn,n,val,fibo
read(*,*) n
Fn_1=0
Fn=1
val=0
if ( n .EQ. 0 ) then
val=0
elseif ( n .EQ. 1 ) then
val=1
elseif ( n .GE. 2 ) then
do 10 i=2, n
val=fibo( Fn_1, Fn)
Fn_1=Fn
Fn=val
10
continue
endif
write(*,*) val
stop
end
Take a look at program-main.s
•
Notice: there are only 6 registers available, they are: $s0, $s1, $s2, $s3, $s4, $s5. If you want to use
more registers, be sure to save them on stack
before using them, and recover them after using them.
Register $s7 can not be used, because it is the offset pointer of translation buffer, see following
example:
li $s2, 0x6f # load ascii character 'o'
sb $s2, translation_buffer($s7)
add $s7, $s7, 1
sb $s2, translation_buffer($s7)
add $s7, $s7, 1
sb $s2, translation_buffer($s7)
add $s7, $s7, 1
sb $t4, translation_buffer($s7)
add $s7, $s7, 1
# save ascii character 'o' to translation buffer
# add the offset by 1 li $s2, 0x70 # load ascii character 'p'
# save ascii character 'p' to translation buffer
# add the offset by 1 li $s2, 0x3a # load ascii character ':'
# save ascii character ':' to translation buffer
# add the offset by 1
# save ascii new line character '0x0a' to translation buffer
# add the offset by 1
Above example shows how to save a word "op:" with a new line symbol to translation buffer
Don’t forget to put newline
symbol!
• When you save MIPS instructions to
translation_buffer, separate line using 0x0a,
or a new line symbol for MIPS assembler to
segment lines.