Dbx 1024 User's Guide download pdf (Page 16)

Chapter 1: Getting Started With dbx

2. Invoke dbx for the failed program as described in “Invoking dbx” on

page 6. dbx automatically reads in the local core ﬁle.

3. Perform a stack trace using the where command (described in

“Examining the Stack” on page 46) to locate the failure point.

For example, suppose you examine the core ﬁle for a program called test.

Suppose the stack trace appears as follows:

(dbx) where

> 0 foo2(i = 5) [“/usr/tmp/test.c”:44, 0x1000109c]

1 foo(i = 4) [“/usr/tmp/test.c”:38, 0x1000105c]

2 main(argc = 1, argv = 0xffffffad78) [“/usr/tmp/test.c”:55, 0x10001104]

3 __start() [“/shamu/crt1text.s”:137, 0x10000ee4]

In this case, test crashed at line 44 of the source ﬁle test.c. The program

crashed while executing the function foo2. foo2 was called from line 38 in

the function foo, which was in turn called from line 55 in the function main.

You can use the other features of dbx to examine values of program variables

and otherwise investigate why test crashed.

If you use dbx to debug code that wasn’t compiled using the –g option, local

variables are invisible to dbx, and source lines may appear to jump around

as a result of various optimizations. If the code is stripped of its debugging

information, dbx displays very little information.

Debugging Your Programs

Debugging a program consists primarily of stopping your program under

certain conditions and then examining the state of the program stack and the

values stored in program variables.

You stop execution of your program by setting breakpoints in your program.

Breakpoints can be unconditional, in which case they always stop your

program when encountered, or conditional, in which case they stop your

program only if a test condition that you specify is true. (See “Setting

Breakpoints” on page 59 for more information.)

To use breakpoints to debug your program, examine your program carefully

to determine where problems are likely to occur, and set breakpoints in these

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Dbx 1024 User's Guide Page 16