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Program organization illustrated using the "Hello World" assembler program

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• EGTAPI label markers
  • The EGTAPI tool requires the assembler program to provide 5 location markers (= labels):

    main: this is the location where the program starts its execution Stop: this is the location where the program ends its execution CodeEnd: this is the location of the last program instruction DataStart: this is the location of the first constant/variable defined in the assembler program DataEnd: this is the location of the last constant/variable defined in the assembler program

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• The "Hello World" assembler program adapted for EGTAPI
  • The following is the Hello World assembler program where I have add the EGTAPUI program markers:

    // // hello-egtapi.s: hello world in ARM assembler for EGTAPI // // How to compile: // // as -o hello-egtapi.o hello-egtapi.s // gcc -o hello-egtapi.arm hello-egtapi.o // .global main .global Stop, CodeEnd, DataStart, DataEnd // ************************ Starting computer instruction **************** .text // *********************************************************************** main: push {lr} // Save the return address on the stack push {fp} // Save the return address on the stack // Explained later in CS255 /* ---------------------------------------- Pass the string to printf function ---------------------------------------- */ movw r0, #:lower16:HelloStr movt r0, #:upper16:HelloStr /* ---------------------------------------- Call the printf function ---------------------------------------- */ bl printf pop {fp} // Pop the frame pointer pop {pc} // Pop the return address // Explained later in CS255 Stop: CodeEnd: nop // ************************ Starting variable definition ***************** .data // *********************************************************************** DataStart: HelloStr: // Label marking this location in memory .asciz "Hello World\n" // ASCII codes for the string DataEnd: .end

    I need to add a nop (no operation) instruction so that the markers Stop and CodeEnd can be recognized by the assembler.

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  • Example Program: (Demo above code)                                                
    • Prog file: /home/cs255/cs255/hello/hello-egtapi.s on host cs255host1

    How to compile the program:

    LabMachine>> /home/cs255001/bin/egtapi 1. Login in as: cs255001 or use your own NetID) 2. Select host "cs255host1" at the end of machine list 3. Login: cs255, pw: abc123 4. File Browser, go to "hello" directory 5. Select hello-egtapi.arm and click COMPILE

    This version of the "Hello World" program can be shown with the EGTAPI tool

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• Installing EGTAPI on your laptop
  • You can download a copy of the EGTAPI tool on your laptop at this URL:

    http://www.cs.emory.edu/~egtapi

    make sure you download the correct version for your laptop (there are version for Linux 64 bits (x64), Linux 32 bits (x86), Mac, Windows 64 bits (x64) and Windows 32 bits (x86))

    You will download a zip file

    Unzip the zip file and you will find the EGTAPI tool inside.

    Click on the icon to run it.

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• Running "Hello World" with EGTAPI
  • If you're working on the workstation in the CS lab, you can run EGTAPI by typing the following command in a terminal window:

    LabMachine>> /home/cs255001/bin/egtapi Instruction to run Hello World on cs255host1: 1. Login in as: cs255001 or use your own NetID) 2. Select host "cs255host1" at the end of machine list 3. Login: cs255, pw: abc123 4. File Browser, go to "hello" directory 5. Select hello-egtapi.arm and click LOAD

    I will demo the EGTAPI tool using the hello-egtapi.arm program.

    In the demo, you will see the following screen in the memory area in the EGTAPI tool:

    This picture shows you that:

    The program instructions of the program are stored starting at the memory address 10408 Hex The constants and variables of the program are stored starting at the memory address 21028 Hex - which is below the program instructions

    So you can see for yourself that this is true:

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  • Quiz:

    Can you see the string "Hello World\n\0" in the Data segment in this picture:

     

     

    Answer:

    48 hex = ASCII code for 'H' 65 hex = ASCII code for 'e' 6c hex = ASCII code for 'l' 6c hex = ASCII code for 'l' 6f hex = ASCII code for 'o' 20 hex = ASCII code for ' ' (space) 57 hex = ASCII code for 'W' 6f hex = ASCII code for 'o' 72 hex = ASCII code for 'r' 6c hex = ASCII code for 'l' 64 hex = ASCII code for 'd' 0a hex = ASCII code for '\n' (newline)