This chapter explains how to examine source files under dbx. It describes:
Based on the information contained in an object file's symbol table, dbx determines from which source files the program was compiled and prints portions of these files as appropriate.
Object files compiled with – g record the absolute path names to the source files. Each time dbx needs a source file, it first searches the absolute path for the source file. If the source file is not present (or if the object file was not compiled with – g), dbx checks its own list of directories for source files.
By default, the dbx directory list contains only the current directory (from which you invoked dbx) and the object file's directory (if it is different from the current directory). Each time dbx searches this list, it searches all directories in the list in the order in which they appear until it finds the file with the specified name.
You can specify additional source directories when you invoke dbx with the – I option. To specify multiple directories, use a separate – I for each.
For example, consider debugging a program called look in /usr/local/bin, the source for which resides in /usr/local/src/look.c. To debug this program, you can invoke dbx from the /usr/local/bin directory by entering:
% dbx -I /usr/local/src look |
The dir and use commands allow you to specify a source directory list while dbx is running.
 | Note: Both the dir and use commands recognize absolute and relative pathnames (for example, ../src); however, they do not recognize C shell tilde (~) syntax (for example, ~kim/src) or environment variables (for example, $HOME/src). |
Let's debug the look program in /usr/local/bin. Recall that the source resides in /usr/local/src/look.c. If you invoke dbx from the /usr/local/bin directory without specifying /usr/local/src as a source directory, it will not initially appear in the directory list:
(dbx) dir . |
However, you can add /usr/local/src with the dir command by entering:
(dbx) dir /usr/local/src (dbx) dir . /usr/local/src |
If you use the use command instead, the current directory is no longer contained in the source directory list:
(dbx) use /usr/local/src (dbx) use /usr/local/src |
Files compiled with – g have full pathnames to source files. If you're debugging a program that was compiled somewhere else and you want to specify a new path to the sources, use path remapping. Just substitute one pattern for another pattern to remap the path so dbx can find the source file.
| dir pattern1:pattern2 |
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For example, a compiled program's source is /x/y/z/kk.c. The source was moved to /x/y/zzz/kk/kk.c. Specify the dir (or use) command to remap the path:
(dbx) dir /z/:/zzz/kk/ |
The new path is /x/y/zzz/kk/kk.c where /z/ is replaced by the path specified after the colon.
The file command changes the current source file to a file that you specify. The new file becomes the current source file, on which you can search, list, and perform other operations. For example, to set the current source file to “Examining the Stack” on page 54procedure.c, enter:
(dbx) file procedure.c |
| Note: If your program is large, typically you store the source code in multiple files. dbx automatically selects the proper source file for the section of code that you are examining. Thus, many dbx commands reset the current source file as a side effect. For example, when you move up and down activation levels in the stack using the up and down commands, dbx changes the current source file to whatever file contains the source for the procedure (see “Examining the Stack” for more information on activation levels). |
If you enter the file command without any arguments, dbx prints the current source file:
(dbx) file procedure.c |
You can also change the current source file by typing:
(dbx) func procedure
You can use the tag command to search the tag file for procedure:
(dbx) tag procedure |
The tag command finds C preprocessor macros if they have arguments
(func procedure cannot). For more information about the tag file, see ctags(1).
The list command displays lines of source code. The dbx variable $listwindow defines the number of lines dbx lists by default. The list command uses the active frame and line of the current source file unless overridden by a file command. Any execution of the program overrides the file command by establishing a new current source file.
The syntax for the list command is:
| list | Lists $listwindow lines beginning at the current line (or list the line of the current pc if the current line is unknown or not set). | |
| list exp | Lists $listwindow lines starting with the line number given by the expression exp. The expression can be any valid expression that evaluates to an integer value as described in “Using Expressions”. | |
| list exp1:exp2 | Lists exp2 lines, beginning at line exp1. | |
| list exp1,exp2 | Lists all source between line exp1 and line exp2 inclusive. | |
| list func | Lists $listwindow lines starting at procedure func. | |
| list func,exp | Lists all source between func and exp, inclusive. | |
| list func:exp | Lists exp lines, beginning at func. |
A > symbol prints to the left of the line that is the current line. A * symbol prints to the left of the line of the current pc location.
For example, to list lines 20–35 of a file, enter:
(dbx) list 20,35 |
In response to this command, dbx displays lines 20 through 35 and sets the current line to 36.
To list 15 lines starting with line 75, enter:
(dbx) list 75:15 |
In response to this command, dbx displays lines 75 through 89 and sets the current line to 90.
Use the forward slash (/) and question mark (?) commands to search through the current file for regular expressions in source code. For a description of regular expressions, see the ed(1) reference page.
The search commands have the following syntax:
For example, to search forward for the next occurrence of the string “errno,” enter:
(dbx) /errno |
To search backward for the previous occurrence of either “img” or “Img,” enter:
(dbx) ?[iI]mg |
The edit command lets you edit files from within dbx:
For example, to edit a file named soar.c from within dbx, type:
(dbx) edit soar.c |
The edit command is also useful for editing dbx script files. See “Executing dbx Scripts” for more information on script files.