Chapter 29 . (Web hosting directory) Programming Tools and Utilities 809
Friday, December 21st, 2007Chapter 29 . Programming Tools and Utilities 809 A core dump refers to an application failing and copying all data stored in memory for the application into a file named core in the current directory. That file can be used to help debug a problem with the application. If you don t see the core dumped message, try executing the shell command ulimit -c unlimited, which allows programs to drop a memory dump in their current working directory. The program has a bug, so you need to debug it. The first step is to start GDB, using the program name, debugme, and the core file, core, as arguments: $ gdb debugme core After GDB initializes, the screen should resemble Figure 29-1. Figure 29-1: GDB s startup screen As you can see near the middle of the figure, GDB displays the name of the executable that created the core file: ` + , . Obviously, the displayed name is wrong; it should be debugme. The odd characters and the incorrect program name would give an experienced developer an immediate clue that the program has a significant memory bug. The next line in the figure, the text that reads Program terminated with signal 11, Segmentation fault, explains why the program terminated. A segmentation fault occurs anytime a program attempts to access memory that doesn t explicitly belong to it. GDB also helpfully displays the function it was executing, index_to_the_moon. If you don t like the licensing messages (they annoy me), use the -q (or –quiet) option when you start GDB to suppress them. Another useful command-line option is -d dirname, where dirname is the name of a directory, which tells gdb where to find source code (it looks in the current working directory by default). Tip Note
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