Difference between revisions of "CSC231 Bash Tutorial 5"
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=Testing Instructions= | =Testing Instructions= | ||
| + | <br /> | ||
| + | Writing a short assembly program to answer quick questions is simple and can be quick. We'll do a couple examples. | ||
| + | <br /> | ||
| + | ==Testing how DIV works== | ||
| + | <br /> | ||
| + | * Get a copy of '''test_skel.asm''' | ||
| + | |||
| + | getcopy test_skel.asm | ||
| + | |||
| + | * Its code is shown below for completeness: | ||
| + | ::<source lang="asm"> | ||
| + | ;;; Testing sandbox | ||
| + | extern _printDec | ||
| + | extern _printString | ||
| + | extern _println | ||
| + | extern _getInput | ||
| + | extern _printRegs | ||
| + | |||
| + | section .data | ||
| + | a dd 100 | ||
| + | b dd 33 | ||
| + | c dd 0 | ||
| + | ans dd 0 | ||
| + | |||
| + | section .text | ||
| + | global _start | ||
| + | _start: ;------------------------------------------------- | ||
| + | |||
| + | |||
| + | ;;; exit ------------------------------------------------- | ||
| + | mov ebx, 0 | ||
| + | mov eax, 1 | ||
| + | int 0x80 | ||
| + | </source> | ||
| + | <br /> | ||
| + | * It has everything needed to test how short pieces of code work. | ||
| + | * Put the following code between the dashed lines: | ||
| + | <br /> | ||
| + | ::<source lang="asm"> | ||
| + | mov edx, 0 | ||
| + | mov eax, dword[a] | ||
| + | div dword[b] | ||
| + | |||
| + | call _printRegs | ||
| + | </source> | ||
| + | * (If the lines are already there, but commented out, just remove the semi-colons.) | ||
| + | * See what the program does. What quantity will be divided by what other quantity. | ||
| + | * Assembly, link and run: | ||
| + | |||
| + | nasm -f elf test_skel.asm | ||
| + | ld -melf_i386 -o test_skel test_skel.o 231Lib.o | ||
| + | ./test_skel | ||
| + | |||
| + | * Do you see the quotient and remainder in the registers? Does it make sense? | ||
| + | <br /> | ||
| + | <tanbox> | ||
| + | You should practice doing this simple exercise every time you are not sure about a particular set of instructions. If you start with a skeleton program, such as '''test_skel.asm''', all you have to do is fill in the middle part, assemble, link and run, and you will have your answer. | ||
| + | <br /> | ||
| + | ==Hex, Binary, and 2's Complement== | ||
| + | <br /> | ||
| + | * You can use the same method for testing number representations. | ||
| + | * Go to this URL [http://www.nasm.us/doc/nasmdoc3.html http://www.nasm.us/doc/nasmdoc3.html], and locate '''Section 3.4.1'''. Look at the instructions and the different ways '''Nasm''' accepts ''literals.'' | ||
| + | * Nasm accepts numbers in decimal, hex, binary, octal, and 2's complements. | ||
| + | * Let's try a few: | ||
| + | * Edit your '''test_skel.asm''' program and add the following lines between the dashed lines: | ||
| + | <br /> | ||
| + | ::<source lang="asm"> | ||
| + | |||
| + | mov eax, 0x0000FFFF | ||
| + | mov ebx, 00000000111111110000000011111111b | ||
| + | mov ecx, 1111_1111_1111_1111_1111_1111_1111_1111b | ||
| + | call _printRegs | ||
| + | |||
| + | |||
| + | </source> | ||
<br /> | <br /> | ||
Revision as of 08:19, 3 March 2017
--D. Thiebaut (talk) 08:04, 3 March 2017 (EST)
Testing Instructions
Writing a short assembly program to answer quick questions is simple and can be quick. We'll do a couple examples.
Testing how DIV works
- Get a copy of test_skel.asm
getcopy test_skel.asm
- Its code is shown below for completeness:
;;; Testing sandbox extern _printDec extern _printString extern _println extern _getInput extern _printRegs section .data a dd 100 b dd 33 c dd 0 ans dd 0 section .text global _start _start: ;------------------------------------------------- ;;; exit ------------------------------------------------- mov ebx, 0 mov eax, 1 int 0x80
- It has everything needed to test how short pieces of code work.
- Put the following code between the dashed lines:
mov edx, 0 mov eax, dword[a] div dword[b] call _printRegs
- (If the lines are already there, but commented out, just remove the semi-colons.)
- See what the program does. What quantity will be divided by what other quantity.
- Assembly, link and run:
nasm -f elf test_skel.asm ld -melf_i386 -o test_skel test_skel.o 231Lib.o ./test_skel
- Do you see the quotient and remainder in the registers? Does it make sense?
<tanbox>
You should practice doing this simple exercise every time you are not sure about a particular set of instructions. If you start with a skeleton program, such as test_skel.asm, all you have to do is fill in the middle part, assemble, link and run, and you will have your answer.
Hex, Binary, and 2's Complement
- You can use the same method for testing number representations.
- Go to this URL http://www.nasm.us/doc/nasmdoc3.html, and locate Section 3.4.1. Look at the instructions and the different ways Nasm accepts literals.
- Nasm accepts numbers in decimal, hex, binary, octal, and 2's complements.
- Let's try a few:
- Edit your test_skel.asm program and add the following lines between the dashed lines:
mov eax, 0x0000FFFF mov ebx, 00000000111111110000000011111111b mov ecx, 1111_1111_1111_1111_1111_1111_1111_1111b call _printRegs
