linux_dsm_epyc7002/tools/perf/arch
Thomas Richter 6738028dd5 perf record: Fix s390 missing module symbol and warning for non-root users
Command 'perf record' and 'perf report' on a system without kernel
debuginfo packages uses /proc/kallsyms and /proc/modules to find
addresses for kernel and module symbols. On x86 this works for root and
non-root users.

On s390, when invoked as non-root user, many of the following warnings
are shown and module symbols are missing:

    proc/{kallsyms,modules} inconsistency while looking for
        "[sha1_s390]" module!

Command 'perf record' creates a list of module start addresses by
parsing the output of /proc/modules and creates a PERF_RECORD_MMAP
record for the kernel and each module. The following function call
sequence is executed:

  machine__create_kernel_maps
    machine__create_module
      modules__parse
        machine__create_module --> for each line in /proc/modules
          arch__fix_module_text_start

Function arch__fix_module_text_start() is s390 specific. It opens
file /sys/module/<name>/sections/.text to extract the module's .text
section start address. On s390 the module loader prepends a header
before the first section, whereas on x86 the module's text section
address is identical the the module's load address.

However module section files are root readable only. For non-root the
read operation fails and machine__create_module() returns an error.
Command perf record does not generate any PERF_RECORD_MMAP record
for loaded modules. Later command perf report complains about missing
module maps.

To fix this function arch__fix_module_text_start() always returns
success. For root users there is no change, for non-root users
the module's load address is used as module's text start address
(the prepended header then counts as part of the text section).

This enable non-root users to use module symbols and avoid the
warning when perf report is executed.

Output before:

  [tmricht@m83lp54 perf]$ ./perf report -D | fgrep MMAP
  0 0x168 [0x50]: PERF_RECORD_MMAP ... x [kernel.kallsyms]_text

Output after:

  [tmricht@m83lp54 perf]$ ./perf report -D | fgrep MMAP
  0 0x168 [0x50]: PERF_RECORD_MMAP ... x [kernel.kallsyms]_text
  0 0x1b8 [0x98]: PERF_RECORD_MMAP ... x /lib/modules/.../autofs4.ko.xz
  0 0x250 [0xa8]: PERF_RECORD_MMAP ... x /lib/modules/.../sha_common.ko.xz
  0 0x2f8 [0x98]: PERF_RECORD_MMAP ... x /lib/modules/.../des_generic.ko.xz

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Link: http://lkml.kernel.org/r/20190522144601.50763-4-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2019-05-28 09:52:23 -03:00
..
alpha perf tools: Add empty Build files for architectures lacking them 2015-08-06 16:24:15 -03:00
arc/annotate perf annotate: Introduce basic support for ARC 2018-12-17 14:59:42 -03:00
arm perf tools: Rename build libperf to perf 2019-02-14 15:18:08 -03:00
arm64 perf arm64: Fix mksyscalltbl when system kernel headers are ahead of the kernel 2019-05-28 09:49:03 -03:00
csky csky: Add support for libdw 2019-05-15 16:36:46 -03:00
mips perf tools: Add empty Build files for architectures lacking them 2015-08-06 16:24:15 -03:00
nds32 perf tools: Rename build libperf to perf 2019-02-14 15:18:08 -03:00
parisc perf tools: Add empty Build files for architectures lacking them 2015-08-06 16:24:15 -03:00
powerpc perf tools: Rename build libperf to perf 2019-02-14 15:18:08 -03:00
s390 perf record: Fix s390 missing module symbol and warning for non-root users 2019-05-28 09:52:23 -03:00
sh perf tools: Rename build libperf to perf 2019-02-14 15:18:08 -03:00
sparc perf tools: Rename build libperf to perf 2019-02-14 15:18:08 -03:00
x86 tools include UAPI: Update copy of files related to new fspick, fsmount, fsconfig, fsopen, move_mount and open_tree syscalls 2019-05-28 09:49:03 -03:00
xtensa perf tools: Rename build libperf to perf 2019-02-14 15:18:08 -03:00
Build perf tools: Rename build libperf to perf 2019-02-14 15:18:08 -03:00
common.c perf annotate: Introduce basic support for ARC 2018-12-17 14:59:42 -03:00
common.h perf machine: Record if a arch has a single user/kernel address space 2018-12-17 14:54:07 -03:00