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Thomas Richter 810f6b9efe perf record: Fix s390 missing module symbol and warning for non-root users 
[ Upstream commit 6738028dd5 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2019-06-22 08:16:17 +02:00
Documentation tcp: add tcp_min_snd_mss sysctl 2019-06-17 19:52:44 +02:00
arch x86/CPU/AMD: Don't force the CPB cap when running under a hypervisor 2019-06-22 08:16:16 +02:00
block block, bfq: increase idling for weight-raised queues 2019-06-15 11:54:58 +02:00
certs Replace magic for trusting the secondary keyring with #define 2018-09-09 19:55:54 +02:00
crypto crypto: ccm - fix incompatibility between "ccm" and "ccm_base" 2019-05-21 18:50:20 +02:00
drivers i2c: dev: fix potential memory leak in i2cdev_ioctl_rdwr 2019-06-22 08:16:17 +02:00
firmware License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fs configfs: Fix use-after-free when accessing sd->s_dentry 2019-06-22 08:16:17 +02:00
include x86/microcode, cpuhotplug: Add a microcode loader CPU hotplug callback 2019-06-19 08:20:59 +02:00
init init: initialize jump labels before command line option parsing 2019-05-16 19:42:23 +02:00
ipc ipc: prevent lockup on alloc_msg and free_msg 2019-06-15 11:54:51 +02:00
kernel perf/ring-buffer: Always use {READ,WRITE}_ONCE() for rb->user_page data 2019-06-22 08:16:16 +02:00
lib test_firmware: Use correct snprintf() limit 2019-06-11 12:21:49 +02:00
mm mm/vmscan.c: fix trying to reclaim unevictable LRU page 2019-06-19 08:20:54 +02:00
net ipvs: Fix use-after-free in ip_vs_in 2019-06-22 08:16:15 +02:00
samples samples: mei: use /dev/mei0 instead of /dev/mei 2019-02-15 08:09:12 +01:00
scripts fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock 2019-06-11 12:21:51 +02:00
security ima: show rules with IMA_INMASK correctly 2019-06-09 09:18:18 +02:00
sound ALSA: hda - Force polling mode on CNL for fixing codec communication 2019-06-22 08:16:17 +02:00
tools perf record: Fix s390 missing module symbol and warning for non-root users 2019-06-22 08:16:17 +02:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM: s390: Do not report unusabled IDs via KVM_CAP_MAX_VCPU_ID 2019-06-09 09:18:16 +02:00
.cocciconfig
…
.get_maintainer.ignore
…
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING
…
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS MAINTAINERS: Add Sasha as a stable branch maintainer 2018-12-01 09:42:50 +01:00
Makefile Linux 4.14.128 2019-06-19 08:21:00 +02:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.