Warnings when building out-of-tree module with -Wsign-compare

[Mauricio Faria de Oliveira]

Bug originally reported and fixes provided by Brian Hart, IBM.

Various warnings will be seen when building an out-of-tree module with -Wsign-compare if any of the following are included:

include/linux/bitops.h
include/linux/cpumask.h
include/linux/fb.h

Seen on post-release 14.04, with current kernel headers.

Example...

Makefile:
----------------------------------------
obj-m := sample.o

EXTRA_CFLAGS = -Wsign-compare
----------------------------------------

sample.c:
----------------------------------------
#include <linux/init.h>
#include <linux/module.h>
#include <linux/bitops.h>
#include <linux/cpumask.h>
#include <linux/fb.h>

MODULE_LICENSE("GPL");

static int sample_init(void)
{
    printk(KERN_ALERT "sample init\n");
    return 0;
}

static void sample_term(void)
{
    printk(KERN_ALERT "sample term\n");
    return;
}

module_init(sample_init)
module_exit(sample_term)
----------------------------------------

$ ARCH=powerpc make -C /usr/src/linux-headers-`uname -r` M=`pwd` modules
...
include/asm-generic/bitops/const_hweight.h:27:70: warning: signed and unsigned type in conditional expression [-Wsign-...
..
include/linux/cpumask.h:603:26: warning: signed and unsigned type in conditional expression [-Wsign-compare]
...
include/linux/fb.h:650:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
...

Fix:
-----

upstream commits:
- bitops.h: linux c32fa99f0b4252633aa464e28d1cb925bd2a79df
- cpumask.h: linux-next cea092c9488cbb22c8b70336ab1413e0daf350f0
- fb.h: linux-next ee3468739ed83d862dbbd90397aff5258f8f2c8e

Patches will be sent to the kernel-team mailing list.

[Mauricio Faria de Oliveira (mfo)]

Patches submitted to the mailing list. [1]

Marking this as confirmed since I confirmed Brian's report.

[1] https://lists.ubuntu.com/archives/kernel-team/2014-May/043098.html

[Mauricio Faria de Oliveira (mfo)]

The e-mail thread mentions 'Trusty SRU' on subject, but not sure where to reflect it on this bug's fields.

[Mauricio Faria de Oliveira (mfo)]

Tim asked for waiting the 2 commits in linux-next to make into linux.

I'll ping him when that happens.

[Brian W Hart (hartb)]

All these changes are now present in Linus' tree:

- bitops.h: linux c32fa99f0b4252633aa464e28d1cb925bd2a79df
- cpumask.h: cea092c9488cbb22c8b70336ab1413e0daf350f0
- fb.h: ee3468739ed83d862dbbd90397aff5258f8f2c8e

[Mauricio Faria de Oliveira (mfo)]

Thanks, Brian.

I just passed along in the kernel-team mailing list, as Tim requested last time.
I'll ping you once there are news.

[Mauricio Faria de Oliveira (mfo)]

... guy is blazing fast; commits in master-next.

[Luis Henriques (henrix)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-trusty' to 'verification-done-trusty'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Mauricio Faria de Oliveira (mfo)]

The packages in proposed fix it.
Thanks.

$ ARCH=powerpc make -C /usr/src/linux-headers-`uname -r` M=`pwd` clean modules 2>&1 | fgrep Wsign-compare
include/linux/bitops.h:77:3641: warning: signed and unsigned type in conditional expression [-Wsign-compare]
include/linux/cpumask.h:603:26: warning: signed and unsigned type in conditional expression [-Wsign-compare]
include/linux/fb.h:650:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
include/linux/bitops.h:77:3641: warning: signed and unsigned type in conditional expression [-Wsign-compare]
include/linux/cpumask.h:603:26: warning: signed and unsigned type in conditional expression [-Wsign-compare]
$

$ sudo apt-get install linux-image-virtual
[...]

$ ARCH=powerpc make -C /usr/src/linux-headers-`uname -r` M=`pwd` clean modules 2>&1 | fgrep Wsign-compare
$

[Mauricio Faria de Oliveira (mfo)]

For the record:

$ uname -r
3.13.0-32-generic

[Brian W Hart (hartb)]

Same result here. Our out-of-tree modules builds without warning on 3.13.0-32-generic from proposed.

Thank you!

Just one note that the repo information in that wiki page doesn't really work for ports. Wiki suggests:

deb http://archive.ubuntu.com/ubuntu/ <release>-proposed restricted main multiverse universe

But what's needed for non-x86/AMD64 is:

deb http://ports.ubuntu.com/ubuntu-ports/ <release>-proposed restricted main multiverse universe

The software-center method isn't a good fit for us because these are display-less servers; we're not really running a desktop environment.

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 3.13.0-32.57

---------------
linux (3.13.0-32.57) trusty; urgency=low

  [ Upstream Kernel Changes ]

  * l2tp: Privilege escalation in ppp over l2tp sockets
    - LP: #1341472
    - CVE-2014-4943

linux (3.13.0-32.56) trusty; urgency=low

  [ Luis Henriques ]

  * Merged back Ubuntu-3.13.0-30.55 security release
  * Revert "x86_64,ptrace: Enforce RIP <= TASK_SIZE_MAX (CVE-2014-4699)"
    - LP: #1337339
  * Release Tracking Bug
    - LP: #1338524

  [ Upstream Kernel Changes ]

  * ptrace,x86: force IRET path after a ptrace_stop()
    - LP: #1337339
    - CVE-2014-4699
  * hpsa: add new Smart Array PCI IDs (May 2014)
    - LP: #1337516

linux (3.13.0-31.55) trusty; urgency=low

  [ Luis Henriques ]

  * Release Tracking Bug
    - LP: #1336278

  [ Andy Whitcroft ]

  * [Config] switch hyper-keyboard to virtual
    - LP: #1325306
  * [Packaging] linux-udeb-flavour -- standardise on linux prefix

  [ dann frazier ]

  * [Config] CONFIG_GPIO_DWAPB=m
    - LP: #1334823

  [ Feng Kan ]

  * SAUCE: (no-up) arm64: dts: Add Designware GPIO dts binding to APM
    X-Gene platform
    - LP: #1334823

  [ John Johansen ]

  * SAUCE: (no-up) apparmor: fix apparmor spams log with warning message
    - LP: #1308761

  [ Kamal Mostafa ]

  * [Config] updateconfigs ACPI_PROCFS_POWER=y after v3.13.11.4 rebase

  [ Loc Ho ]

  * SAUCE: (no-up) phy-xgene: Use correct tuning for Mustang
    - LP: #1335636

  [ Michael Ellerman ]

  * SAUCE: (no-up) powerpc/perf: Ensure all EBB register state is cleared
    on fork()
    - LP: #1328914

  [ Ming Lei ]

  * Revert "SAUCE: (no-up) rtc: Add X-Gene SoC Real Time Clock Driver"
    - LP: #1274305

  [ Suman Tripathi ]

  * SAUCE: (no-up) libahci: Implement the function ahci_restart_engine to
    restart the port dma engine.
    - LP: #1335645
  * SAUCE: (no-up) ata: Fix the dma state machine lockup for the IDENTIFY
    DEVICE PIO mode command.
    - LP: #1335645

  [ Tim Gardner ]

  * [Config] CONFIG_POWERNV_CPUFREQ=y for powerpc, ppc64el
    - LP: #1324571
  * [Debian] Add UTS_UBUNTU_RELEASE_ABI to utsrelease.h
    - LP: #1327619
  * [Config] CONFIG_HAVE_MEMORYLESS_NODES=y
    - LP: #1332063
  * [Config] CONFIG_HID_RMI=m
    - LP: #1305522

  [ Upstream Kernel Changes ]

  * Revert "offb: Add palette hack for little endian"
    - LP: #1333430
  * Revert "net: mvneta: fix usage as a module on RGMII configurations"
    - LP: #1333837
  * Revert "USB: serial: add usbid for dell wwan card to sierra.c"
    - LP: #1333837
  * Revert "macvlan : fix checksums error when we are in bridge mode"
    - LP: #1333838
  * serial: uart: add hw flow control support configuration
    - LP: #1328295
  * mm/numa: Remove BUG_ON() in __handle_mm_fault()
    - LP: #1323165
  * Tools: hv: Handle the case when the target file exists correctly
    - LP: #1306215
  * Documentation/devicetree/bindings: add documentation for the APM X-Gene
    SoC RTC DTS binding
    - LP: #1274305
  * drivers/rtc: add APM X-Gene SoC RTC driver
    - LP: #1274305
  * arm64: add APM X-Gene SoC RTC DTS entry
    - LP: #1274305
  * powerpc/perf: Add Power8 cache & TLB events
    - LP: #1328914
  * powerpc/perf: Configure BH...