Linux Kernel: Print Callee and Caller

Print the callback function name

If you cannot trace which function gets called when you call from core driver using function pointer, you can print function name using pf format specifier.
Linux maintains symbol table so based on function address, it can identify function name based on address pointed by function pointer.
e.g. Core driver calls hardware specific enable/disable functions:
core->ops->enable(). If you are not sure, which function is executed as a result of this call, you can print them using %pf or %pF:
pr_info("callee function name is: %pf,  core->ops->enable)
%pf prints without offset (e.g. foo) while %pF prints with offset (e.g. foo+0x00/0x80)
Reference: https://www.kernel.org/doc/Documentation/printk-formats.txt.
Thanks Bhargav(br13patel) for sharing this!

Print caller name

There are few ways to trace caller in Linux kernel.
  • Print stack backtrace
    • dump_stack();
      • To enable the dump_stack() function in the kernel config the following options must be set.
        1. Kernel hacking -> Kernel debugging
        2. Kernel hacking -> Verbose kernel error messages
    • WARN_ON(1);
  • Print caller name
    • pr_info(“caller function name is: %pf,  __builtin_return_address(0))
Advertisements