Lecture XXIV: Review Xuan Guo CSC 3210 Computer Organization and Programming Georgia State University April 23, 2015 Xuan Guo Lecture XXIV: Review

Transcription

1 CSC 3210 Computer Organization and Programming Georgia State University April 23, 2015

2 This lecture Review: set instruction register saving subroutine linkage arguments passing printf function instruction encoding and decoding subroutine design (2 questions, 50 points)

3 set Instruction The above pair of instructions is used quite a lot, so the assembler provides a "synthetic instruction" which will generate them for you. The "instruction" set const32, %reg will accept any 32-bit constant (const32) such as an address, and any register (%reg) and will generate sethi or %hi(const32),%reg %reg,%lo(const32),%reg However, it should be remembered that SET is not a real SPARC instruction, and that it produces two machine language instructions, not one. Lecture XXII: I/O (2)

4 Stack The figure below shows a set of 128 registers and 24 of them mapped as in, local and out. Show the mapping after 4 save and 2 restore instructions. You have to show the positions for new in, local and out registers, the new positions for cwp and wim. Lecture XX: Subroutines (3)

5 Arguments to Subroutines 64 bytes for saving 16 registers starting at %sp 4 bytes for structure return pointer at %sp bytes for 6 arguments starting at %sp additional arguments may be placed on stack starting at %sp + 92 and can be accessed by the called subroutine at %fp + 92 Stand format for writing subroutine:.global subroutine_name: subroutine_name: save %sp, -( more_args + local ) & -8, %sp In, SPARC first 6 arguments can be placed in the out registers. Only 6 out registers are available since %o6 is stack pointer and %o7 is used for storing calling address. Lecture XX: Subroutines (3)

6 Example Assuming you need 9 arguments (word type) to be passed to a subroutine that you are calling from main, and you need memory space for the following variables in main. What is the total size of stack required for the main subroutine? int a, b short c char d Lecture XX: Subroutines (3)

7 Subroutine Linkage The SPARC architecture supports two instructions, call and jmpl, for linking to subroutines In SPARC,two instructions for linking to subroutine which save the address of calling instruction in %o7. return is to the address pointed by %o inside the subroutine, since o7 is mapped to i7, the return is made to %i7+8.

8 The ret is expanded to: jmpl %i7 + 8, %g0 call %o0 is expanded as jmpl %o0, %o7 to call a subroutine whose address is in register %o0 and to store the return address into %o7, we would write: jmpl %o0, %o7

9 Printing a string To use printf to print a string, the address of the substituted string must be in the correspondent register. Example:!assuming your strings are in data section as follows mystring:.asciz Hello %s! name:.asciz Michael...! and your code should be set mystring, %o0! address of the output set name, %o1! Address of the substituted string call printf! Will print Hello Michael! nop Lecture XXI: I/O (1)

10 SPARC Instructions are 32 bits long

11 Bonus round Decode the following commands: 1. 0x9de3bfa0 2. 0x x81c7e008

12 Write a closed subroutine arraycreate that allocates a block of memory on stack for a 1- dimensional array of 10 elements. The array contains only word-size (4 bytes) elements. Your subroutine should initialize the old elements of this array to 1

13 Write a closed subroutine factorial in an assembly level language to find the factorial of a number. For example, if number 5 is in %o0 in caller routine, the output should be 5! = 5*4*3*2*1 = 120. The output should be stored in %o1 in caller routine

14 Write a LEAF subroutine that takes an input number in %o0 and return 0 if the given number is odd and positive; otherwise, return -1. The returning value should be in %o0.