The pid provider lets you trace any instruction in a function. For example to trace the instruction 4 bytes into a function main, you could use a command similar to the following example:
pid123:a.out:main:4
Every time the program executes the instruction at address main+4, this probe will be activated. The arguments for offset probes are undefined. The uregs[] array will help you examine process state at these probe sites. See uregs[] Array for more information.