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.
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
