On 2/09/19 5:15 PM, Leo Yan wrote: > Hi Adrian, > > On Mon, Aug 26, 2019 at 08:51:05PM +0800, Leo Yan wrote: >> Hi Adrian, >> >> On Fri, Aug 16, 2019 at 04:00:02PM +0300, Adrian Hunter wrote: >>> On 16/08/19 4:45 AM, Leo Yan wrote: >>>> Hi Adrian, >>>> >>>> On Thu, Aug 15, 2019 at 02:45:57PM +0300, Adrian Hunter wrote: >>>> >>>> [...] >>>> >>>>>>> How come you cannot use kallsyms to get the information? >>>>>> >>>>>> Thanks for pointing out this. Sorry I skipped your comment "I don't >>>>>> know how you intend to calculate ARM_PRE_START_SIZE" when you reviewed >>>>>> the patch v3, I should use that chance to elaborate the detailed idea >>>>>> and so can get more feedback/guidance before procceed. >>>>>> >>>>>> Actually, I have considered to use kallsyms when worked on the previous >>>>>> patch set. >>>>>> >>>>>> As mentioned in patch set v4's cover letter, I tried to implement >>>>>> machine__create_extra_kernel_maps() for arm/arm64, the purpose is to >>>>>> parse kallsyms so can find more kernel maps and thus also can fixup >>>>>> the kernel start address. But I found the 'perf script' tool directly >>>>>> calls machine__get_kernel_start() instead of running into the flow for >>>>>> machine__create_extra_kernel_maps(); >>>>> >>>>> Doesn't it just need to loop through each kernel map to find the lowest >>>>> start address? >>>> >>>> Based on your suggestion, I worked out below change and verified it >>>> can work well on arm64 for fixing up start address; please let me know >>>> if the change works for you? >>> >>> How does that work if take a perf.data file to a machine with a different >>> architecture? >> >> Sorry I delayed so long to respond to your question; I didn't have >> confidence to give out very reasonale answer and this is the main reason >> for delaying. > > Could you take chance to review my below replying? I'd like to get > your confirmation before I send out offical patch. It is not necessary to do kallsyms__parse for x86_64, so it would be better to check the arch before calling that. However in general, having to copy and use kallsyms with perf.data if on a different arch does not seem very user friendly. But really that is up to Arnaldo. > > Thanks, > Leo Yan > >> >> For your question for taking a perf.data file to a machine with a >> different architecture, we can firstly use command 'perf buildid-list' >> to print out the buildid for kallsyms, based on the dumped buildid we >> can find out the location for the saved kallsyms file; then we can use >> option '--kallsyms' to specify the offline kallsyms file and use the >> offline kallsyms to fixup kernel start address. The detailed commands >> are listed as below: >> >> root@debian:~# perf buildid-list >> 7b36dfca8317ef74974ebd7ee5ec0a8b35c97640 [kernel.kallsyms] >> 56b84aa88a1bcfe222a97a53698b92723a3977ca /usr/lib/systemd/systemd >> 0956b952e9cd673d48ff2cfeb1a9dbd0c853e686 /usr/lib/aarch64-linux-gnu/libm-2.28.so >> [...] >> >> root@debian:~# perf script --kallsyms ~/.debug/\[kernel.kallsyms\]/7b36dfca8317ef74974ebd7ee5ec0a8b35c97640/kallsyms >> >> The amended patch is as below, please review and always welcome >> any suggestions or comments! >> >> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c >> index 5734460fc89e..593f05cc453f 100644 >> --- a/tools/perf/util/machine.c >> +++ b/tools/perf/util/machine.c >> @@ -2672,9 +2672,26 @@ int machine__nr_cpus_avail(struct machine *machine) >> return machine ? perf_env__nr_cpus_avail(machine->env) : 0; >> } >> >> +static int machine__fixup_kernel_start(void *arg, >> + const char *name __maybe_unused, >> + char type, >> + u64 start) >> +{ >> + struct machine *machine = arg; >> + >> + type = toupper(type); >> + >> + /* Fixup for text, weak, data and bss sections. */ >> + if (type == 'T' || type == 'W' || type == 'D' || type == 'B') >> + machine->kernel_start = min(machine->kernel_start, start); >> + >> + return 0; >> +} >> + >> int machine__get_kernel_start(struct machine *machine) >> { >> struct map *map = machine__kernel_map(machine); >> + char filename[PATH_MAX]; >> int err = 0; >> >> /* >> @@ -2696,6 +2713,22 @@ int machine__get_kernel_start(struct machine *machine) >> if (!err && !machine__is(machine, "x86_64")) >> machine->kernel_start = map->start; >> } >> + >> + if (symbol_conf.kallsyms_name != NULL) { >> + strncpy(filename, symbol_conf.kallsyms_name, PATH_MAX); >> + } else { >> + machine__get_kallsyms_filename(machine, filename, PATH_MAX); >> + >> + if (symbol__restricted_filename(filename, "/proc/kallsyms")) >> + goto out; >> + } >> + >> + if (kallsyms__parse(filename, machine, machine__fixup_kernel_start)) >> + pr_warning("Fail to fixup kernel start address. skipping...\n"); >> + >> +out: >> return err; >> } >> >> >> Thanks, >> Leo Yan >