Hi Everyone, With systemTap, in the absence of debugging information (DWARF), one can access function parameters using (positional) numbers. Can the same be done with `perf`? Why? I'm trying to capture variables in a kernel function but I don't have an good perf with DWARF support and there is are significant challenges to build one due to the relatively old distro.
Thanks, Jun Details on the SystemTap way of doing that can be referred to at https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/5/html/SystemTap_Language_Reference/ch04s03.html 4.3. DWARF-less probing In the absence of debugging information, you can still use the /kprobe/ family of probes to examine the entry and exit points of kernel and module functions. You cannot look up the arguments or local variables of a function using these probes. However, you can access the parameters by following this procedure: When you're stopped at the entry to a function, you can refer to the function's arguments by number. For example, when probing the function declared: asmlinkage ssize_t sys_read(unsigned int fd, char __user * buf, size_t count) You can obtain the values of |fd|, |buf|, and |count|, respectively, as |uint_arg(1)|, |pointer_arg(2)|, and |ulong_arg(3)|. In this case, your probe code must first call |asmlinkage()|, because on some architectures the asmlinkage attribute affects how the function's arguments are passed. When you're in a return probe, $|return| isn't supported without DWARF, but you can call |returnval()| to get the value of the register in which the function value is typically returned, or call |returnstr()| to get a string version of that value. -- To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
