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Development Tips

Here you will find various tips useful while development and debugging.

Breakpoint on a specific packet number

Often you know, that you have a bug/problem in your dissector, which can be found only in a specific packet.

Let's say you know packet number 1234 has a bug, so you can add the following to your code:

{{{ if(pinfo->fd->num == 1234) {

} }}}

and simply set a breakpoint to the printf call.

Of course you will need access to pinfo, but this should be the case in any dissector.

Don't forget to remove this later, after you've found your bug :-)

Some debuggers, such as gdb and MSVC, also let you make breakpoints conditional; you could set a breakpoint at some point in a routine, and make the condition for the breakpoint be pinfo->fd->num == 1234.

Using MSVC++ for debugging

Extracted from

If you are just wanting to debug Ethereal then the Win32 binaries should already include the debug symbols by default. You can look at the file config.nmake and ensure that the debug switch is enabled...

# Linker flags
# /DEBUG generate debug info

Once you have a valid binary with debug symbols you can easily debug Ethereal by opening up the binary from within MSVC.

So from within Visual Studio just click on the file/open menu, change the file extension type to be all files, then browse to the installed location of the Ethereal binary. Typically, c:\program files\ethereal... Once you have it open you should see ethereal.exe listed in the far left window of Visual Studio. To execute Ethereal just press the F5 key. If you want to break within some location within Ethereal then just open a source file and set a break point. The execution of Ethereal.exe will halt at the specific location. You can then step through the source code to isolate/debug you issue.

Using MSVC++ "source browser" capability

It is sometimes quite useful to be able to use the "Tools ! Source Browser" capability of MSVC to find the defintions and references for Ethereal functions and variables.

To build and use the required "Browse Information File" (.bsc) file:

  1. Change config.nmake to add the /Fr switch to the compiler flags (in addition to the /DEBUG linker flags change described above).

# Compiler flags
# /W3  warning level 3 (0 less - 4 most, 1 default) 
# /Zi  create .pdb file for debugging 
# /FR  create .sbr files used by BSCMAKE to create a "Browse Information File"  
  1. Build ethereal using nmake as usual
  2. Create the .BSC file as follows

 bscmake /o ethereal.bsc *.sbr epan\*.sbr epan\dfilter\*.sbr ^
 epan\ftypes\*.sbr epan\dissectors\*.sbr gtk2.tmp\*.sbr wiretap\*.sbr
  1. Open the Ethereal binary from within Visual Studio as described above; Select Tools ! Source Browser from the Toolbar; Enter a valid identifier and select OK to get a list of the source location (file name and line number) of the definitions and references for the identifier.

By using the keyboard shortcuts associated with the source browser it is possible to quite easily navigate through source files. (See MSVC "Browse Information Files" Help).

For example: If the cursor is located at the beginning of an identifier, entering F12 will go immediately to the source file location of the definition of the identifier. Entering <Ctrl Num *> will then move the cursor back to the previous location.