1 / 15

Debuggers

Debuggers. A program needed when writing any type of code Displays the contents of memory Lets you view registers and variables and see how they change Allows tracing (stepping through a program one line at a time). Debug. A debugger supplied with both DOS and Windows Debug.exe

lila-williams
Download Presentation

Debuggers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Debuggers • A program needed when writing any type of code • Displays the contents of memory • Lets you view registers and variables and see how they change • Allows tracing (stepping through a program one line at a time)

  2. Debug • A debugger supplied with both DOS and Windows • Debug.exe • Found in \Windows\command • Command line driven • A precursor of Microsoft Codeview, Borland Turbo Debugger, Visual Studio Debuggers, Periscope, Atron, SYMDEB, Codesmith-86, Advanced-Trace-86

  3. Assembly Level Debugger • Debug is an assembly level debugger • Displays only assembly mnemonics and machine instructions. C> debug sample.exe Sample.exe Debug.exe DOS 0000

  4. Debugging Functions • Assemble short programs • View a program’s source code along with its machine language • View the CPU registers and flags • Trace or execute a program, watching variables for changes • Enter new values into memory • Search for binary or ASCII values in memory • Move a block of memory from one location to another • Fill a block of memory • Load and write disk files and sectors

  5. Debug Commands • Can be divided into four categories • Program creation/debugging • Memory manipulation • Miscellaneous • Input-output

  6. Command Parameters • Addresses • can be given as either a complete segment-offset or just an offset • Segment portion may be a hex number or a register name • F000:100 segment, offset • DS:200 segment register, offset • 0AF5 offset

  7. Command Parameters • Address Ranges • Format 1: address [.address] • 100, 500 • CS:200, 300 • 200 • Format 2: address L [value] • 100 L 20 (20h bytes starting at location 100h)

  8. Command Parameters • Strings – a sequence of characters enclosed in single or double quotes. • ‘command’ • “File can not be opened.” • Filespec – • B:prog1.com • C:\asm\progs\test.com • File1 • Values – consists of 1- to 4-character hex number.

  9. Example commands • -D (Dump) • Displays memory on the screen as single bytes in both hex and ASCII No range given => dumps 128 bytes from last referenced location -d 0-200 => dumps offsets 0-200 from DS -d SS:0 5 => dumps the bytes at offsets 0-5 from SS. -d 915:0 => dumps 128 bytes from segment 0915h

  10. Example Commands • -R (Registers) -r =>display the contents of all registers -r IP => display the contents of IP and prompt for a new value -r CX => display the contents of CX and prompt for a new value -r F => display all flags and prompt for a new flag value.

  11. Set OV = Overflow DN = Direction Down EI = Interrupts enabled NG = Sign Flag negative ZR = Zero AC = Auxiliary Carry PO = Odd Parity CY= Carry Clear NV = No Overflow UP = Direction Up DI = Interrupts Disabled PL = Sign Flag Positive NZ = Not Zero NA = No Auxiliary Carry PE = Even Parity NC = No Carry Flags

  12. Example Commands • A (Assemble) • Assemble a program into machine language • A 100 => assemble at CS:100 • A => assemble from the current location • A DS:2000 => Assemble at DS:2000h • Pressing enter at the end of a line, returns a prompt for the next line of input. To terminate input, press the Enter key on a blank line. -a 100 5514:0100 mov ah, 2 5514:0102 mov dl, 41 5514:0104 int 21 5514:0106

  13. Example Commands • -T (Trace) executes one or more instructions starting at either the current CS:IP location or at an optional address. -t => trace the next instruction -t 5 => trace the next five instructions -t =105 10 => trace 16 instructions starting at CS:105

  14. Segment Defaults

  15. Lab #1 and Lab #2 • First two labs will allow you to explore using Debug.

More Related