On 12/1/13, 11:15 PM, Masami Hiramatsu wrote: > (2013/12/02 9:07), David Ahern wrote: >> Allow user to specify an address within an executable. This is useful, for >> example, in probing local functions. If the function name begins with 0x >> then try to convert the supplied name to an address. If succuessful then >> treat the function name as the address within the executable to be probed. > > Hmm, IMHO, this kind of functionality is only good for debugging.
Why? perf-probe takes the function name, looks up the address in the executable, adds an offset and then pushes that address to the kernel. Why can't I have an option to jump straight to the desired address? A few use cases that come to mind: 1. Allows manual creation of return probes in kernels which do not have that support. 2. probing static functions 3. probing versioned addresses in libc -- something the current syntax does not allow because '@' is used as a field separator: $ nm /lib64/libc-2.14.90.so | grep pthread_cond_timedwait 00000000000fe6c0 t __pthread_cond_timedwait 000000000012d920 t __pthread_cond_timedwait_2_0 00000000000fe6c0 T pthread_cond_timedwait@@GLIBC_2.3.2 000000000012d920 T pthread_cond_timedwait@GLIBC_2.2.5 $ perf probe -x /lib64/libc-2.14.90.so -a 'cond_timewait=pthread_cond_timedwait' no symbols found in /lib64/libc-2.14.90.so, maybe install a debug package? Failed to load map. Error: Failed to add events. (-22) $ perf probe -x /lib64/libc-2.14.90.so -a 'cond_timewait=pthread_cond_timedwait@@GLIBC_2.3.2' Semantic error :SRC@SRC is not allowed. 4. A workaround for any other shortcomings in the interface that require patches to fix and backports to be done. backports which take time if even possible. > In that case, you should use uprobe_events interface directly. How do I do that within the context of perf? > > I recommend you to try enabing dwarf support in user space. > Perf probe is a user-friendly interface of dynamic events. I do have dwarf support enabled in perf. Are you referring to other components of userspace (like system libraries)? David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
