On 12/2/13, 7:49 AM, David Ahern wrote: > 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
D'oh. That is supposed to be local functions, not static functions. Right now perf-probe does not allow probes in local functions of an executable. Giving a specific address provides a mean to do that. > > 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/
