At some point in the past we needed to make sure we would get the long
name of modules and not just what we get from /proc/modules, but that
need, as described in the cset that introduced the adjustment function:

Fixes: c03d5184 ("perf machine: Adjust dso->long_name for offline module")

Without using the buildid-cache:

  # lsmod | grep trusted
  # insmod trusted.ko
  # lsmod | grep trusted
  trusted                24576  0
  # strace -e open,openat perf probe -m ./trusted.ko key_seal |& grep trusted
  openat(AT_FDCWD, "/sys/module/trusted/notes/.note.gnu.build-id", O_RDONLY) = 4
  openat(AT_FDCWD, "/sys/module/trusted/notes/.note.gnu.build-id", O_RDONLY) = 7
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "/root/.debug/root/trusted.ko/dd3d355d567394d540f527e093e0f64b95879584/probes", O_RDWR|O_CREAT, 0644) = 3
  openat(AT_FDCWD, "/usr/lib/debug/root/trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/usr/lib/debug/root/trusted.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/root/.debug/trusted.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, ".debug/trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 4
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
    probe:key_seal       (on key_seal in trusted)
  # perf probe -l
    probe:key_seal       (on key_seal in trusted)
  #

No attempt at opening '[trusted]'.

Now using the build-id cache:

  # rmmod trusted
  # perf buildid-cache --add ./trusted.ko
  # insmod trusted.ko
  # strace -e open,openat perf probe -m ./trusted.ko key_seal |& grep trusted
  openat(AT_FDCWD, "/sys/module/trusted/notes/.note.gnu.build-id", O_RDONLY) = 4
  openat(AT_FDCWD, "/sys/module/trusted/notes/.note.gnu.build-id", O_RDONLY) = 7
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "/root/.debug/root/trusted.ko/dd3d355d567394d540f527e093e0f64b95879584/probes", O_RDWR|O_CREAT, 0644) = 3
  openat(AT_FDCWD, "/usr/lib/debug/root/trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/usr/lib/debug/root/trusted.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/root/.debug/trusted.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, ".debug/trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "trusted.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 4
  openat(AT_FDCWD, "/root/trusted.ko", O_RDONLY) = 3
  #

Again, no attempt at reading '[trusted]'.

Finally, adding a probe to that function and then using:

[root@quaco ~]# perf trace -e probe_perf:*/max-stack=16/ --max-events=2
     0.000 perf/13456 probe_perf:dso__adjust_kmod_long_name(__probe_ip: 5492263)
                                       dso__adjust_kmod_long_name (/home/acme/bin/perf)
                                       machine__process_kernel_mmap_event (/home/acme/bin/perf)
                                       machine__process_mmap_event (/home/acme/bin/perf)
                                       perf_event__process_mmap (/home/acme/bin/perf)
                                       machines__deliver_event (/home/acme/bin/perf)
                                       perf_session__deliver_event (/home/acme/bin/perf)
                                       perf_session__process_event (/home/acme/bin/perf)
                                       process_simple (/home/acme/bin/perf)
                                       reader__process_events (/home/acme/bin/perf)
                                       __perf_session__process_events (/home/acme/bin/perf)
                                       perf_session__process_events (/home/acme/bin/perf)
                                       process_buildids (/home/acme/bin/perf)
                                       record__finish_output (/home/acme/bin/perf)
                                       __cmd_record (/home/acme/bin/perf)
                                       cmd_record (/home/acme/bin/perf)
                                       run_builtin (/home/acme/bin/perf)
     0.055 perf/13456 probe_perf:dso__adjust_kmod_long_name(__probe_ip: 5492263)
                                       dso__adjust_kmod_long_name (/home/acme/bin/perf)
                                       machine__process_kernel_mmap_event (/home/acme/bin/perf)
                                       machine__process_mmap_event (/home/acme/bin/perf)
                                       perf_event__process_mmap (/home/acme/bin/perf)
                                       machines__deliver_event (/home/acme/bin/perf)
                                       perf_session__deliver_event (/home/acme/bin/perf)
                                       perf_session__process_event (/home/acme/bin/perf)
                                       process_simple (/home/acme/bin/perf)
                                       reader__process_events (/home/acme/bin/perf)
                                       __perf_session__process_events (/home/acme/bin/perf)
                                       perf_session__process_events (/home/acme/bin/perf)
                                       process_buildids (/home/acme/bin/perf)
                                       record__finish_output (/home/acme/bin/perf)
                                       __cmd_record (/home/acme/bin/perf)
                                       cmd_record (/home/acme/bin/perf)
                                       run_builtin (/home/acme/bin/perf)
  #

This was the only path I could find using the perf tools that reach at this
function, then as of november/2019, if we put a probe in the line where the
actuall setting of the dso->long_name is done:

  # perf trace -e probe_perf:*
  ^C[root@quaco ~]
  # perf stat -e probe_perf:*  -I 2000
       2.000404265                  0      probe_perf:dso__adjust_kmod_long_name
       4.001142200                  0      probe_perf:dso__adjust_kmod_long_name
       6.001704120                  0      probe_perf:dso__adjust_kmod_long_name
       8.002398316                  0      probe_perf:dso__adjust_kmod_long_name
      10.002984010                  0      probe_perf:dso__adjust_kmod_long_name
      12.003597851                  0      probe_perf:dso__adjust_kmod_long_name
      14.004113303                  0      probe_perf:dso__adjust_kmod_long_name
      16.004582773                  0      probe_perf:dso__adjust_kmod_long_name
      18.005176373                  0      probe_perf:dso__adjust_kmod_long_name
      20.005801605                  0      probe_perf:dso__adjust_kmod_long_name
      22.006467540                  0      probe_perf:dso__adjust_kmod_long_name
  ^C    23.683261941                  0      probe_perf:dso__adjust_kmod_long_name

  #

Its not being used at all.

To further test this I used kvm.ko as the offline module, i.e. removed
if from the buildid-cache by nuking it completely (rm -rf ~/.debug) and
moved it from the normal kernel distro path, removed the modules, stoped
the kvm guest, and then installed it manually, etc.

  # rmmod kvm-intel
  # rmmod kvm
  # lsmod | grep kvm
  # modprobe kvm-intel
  modprobe: ERROR: ctx=0x55d3b1722260 path=/lib/modules/5.3.8-200.fc30.x86_64/kernel/arch/x86/kvm/kvm.ko.xz error=No such file or directory
  modprobe: ERROR: ctx=0x55d3b1722260 path=/lib/modules/5.3.8-200.fc30.x86_64/kernel/arch/x86/kvm/kvm.ko.xz error=No such file or directory
  modprobe: ERROR: could not insert 'kvm_intel': Unknown symbol in module, or unknown parameter (see dmesg)
  # insmod ./kvm.ko
  # modprobe kvm-intel
  modprobe: ERROR: ctx=0x562f34026260 path=/lib/modules/5.3.8-200.fc30.x86_64/kernel/arch/x86/kvm/kvm.ko.xz error=No such file or directory
  modprobe: ERROR: ctx=0x562f34026260 path=/lib/modules/5.3.8-200.fc30.x86_64/kernel/arch/x86/kvm/kvm.ko.xz error=No such file or directory
  # lsmod | grep kvm
  kvm_intel             299008  0
  kvm                   765952  1 kvm_intel
  irqbypass              16384  1 kvm
  #
  # perf probe -x ~/bin/perf machine__findnew_module_map:12 mname=m.name:string filename=filename:string 'dso_long_name=map->dso->long_name:string' 'dso_name=map->dso->name:string'
  # perf probe -l
    probe_perf:machine__findnew_module_map (on machine__findnew_module_map:12@util/machine.c in /home/acme/bin/perf with mname filename dso_long_name dso_name)
  # perf record
  ^C[ perf record: Woken up 2 times to write data ]
  [ perf record: Captured and wrote 3.416 MB perf.data (33956 samples) ]
  # perf trace -e probe_perf:machine*
  <SNIP>
       6.322 perf/23099 probe_perf:machine__findnew_module_map(__probe_ip: 5492493, mname: "[salsa20_generic]", filename: "/lib/modules/5.3.8-200.fc30.x86_64/kernel/crypto/salsa20_generic.ko.xz", dso_long_name: "/lib/modules/5.3.8-200.fc30.x86_64/kernel/crypto/salsa20_generic.ko.xz", dso_name: "[salsa20_generic]")
       6.375 perf/23099 probe_perf:machine__findnew_module_map(__probe_ip: 5492493, mname: "[kvm]", filename: "[kvm]", dso_long_name: "[kvm]", dso_name: "[kvm]")
  <SNIP>

The filename doesn't come with the path, no point in trying to set the dso->long_name.

  [root@quaco ~]# strace -e open,openat perf probe -m ./kvm.ko kvm_apic_local_deliver |& egrep 'open.*kvm'
  openat(AT_FDCWD, "/sys/module/kvm_intel/notes/.note.gnu.build-id", O_RDONLY) = 4
  openat(AT_FDCWD, "/sys/module/kvm/notes/.note.gnu.build-id", O_RDONLY) = 4
  openat(AT_FDCWD, "/lib/modules/5.3.8-200.fc30.x86_64/kernel/arch/x86/kvm", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 7
  openat(AT_FDCWD, "/sys/module/kvm_intel/notes/.note.gnu.build-id", O_RDONLY) = 8
  openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "/root/.debug/root/kvm.ko/5955f426cb93f03f30f3e876814be2db80ab0b55/probes", O_RDWR|O_CREAT, 0644) = 3
  openat(AT_FDCWD, "/usr/lib/debug/root/kvm.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/usr/lib/debug/root/kvm.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/root/.debug/kvm.ko", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "kvm.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, ".debug/kvm.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "kvm.ko.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 3
  openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 4
  openat(AT_FDCWD, "/root/kvm.ko", O_RDONLY) = 3
  [root@quaco ~]#

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-jlfew3lyb24d58egrp0o72o2@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>