Geep Gdb Basics 24thfeb08

Using the GNU Debugger (GDB) Pranav Peshwe

Techzemplary Pvt.Ltd February 24th 2008

Some background about GDB... ●

Started by RMS in 1986

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Ported to all major OSes thereafter

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Has support for almost all popular architectures

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Supports symbolic debugging

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Primarily used for debugging C/C++

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Supports remote debugging

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Work being done on bringing in 'Reversible debugging'

Getting ready... ●

Compiling with debug information

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Side effects of debug information

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Readying multi-file projects for debugging

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Nifty utililies – file, nm, objdump, strip etc

A typical debug workflow ●

Run

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Backtrace

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Break

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Step

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Inspect

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Change

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Continue

Preliminary usage ●

The GDB executable - /usr/bin/gdb

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To start – gdb [program-name]

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To quit – quit

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Select a program to run – file <prog-name>

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Run a program in gdb - run

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Kill a prog in gdb – kill <prog-name>

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Getting help – GDB manual and online help

Zeroing on the function ●

Backtracing ­ bt

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Moving between frames – up, down and frame

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Viewing arguments' addresses – info args

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Other information about the frame – info frame

Looking at the source ●

Specifying the source file(s) – directory

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Listing the source – the many variants of list

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Searching the source – search

Breaking into the code ●

Breakpoint on a function – b func_name, continue

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Breakpoint on a source line – b [filename:]line_no

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Listing current breakpoints – info b

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Break only the first time – tbreak

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Ignore, disable and delete breakpoints

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Watchpoints

Moving ahead...one step at a time ●

Single stepping – step, next

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'finish'ing a function

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Forcing a return

Inspecting data ●

Global variables – info variables

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Local variables – info locals

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Examining values of variables – print

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Viewing arrays

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Automatic display

Inspecting data contd... ●

Examining memory - x

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Viewing registers – info registers

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Listing functions

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Listing variables in scope of a function

On­site debugging ?? ●

Get the pid of the process

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Attach to a running process – attach

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Loading symbol table from an external file

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Detach from a running process – detach

Miscellaneous stuff ●

Getting runtime information

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Redirecting output

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Logging

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Shell commands

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Graphical front-ends to GDB

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Delta debugging B)

END OF PART I Questions welcome...