Turning on this flag could prevent the compiler from optimising away
some "useless" checks for null pointers. Such bugs can sometimes become
exploitable at compile time because of the -O2 optimisation.
See http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Optimize-Options.html
An example that clearly shows this 'problem' is commit 6bf67672.
static void __devexit agnx_pci_remove(struct pci_dev *pdev)
{
struct ieee80211_hw *dev = pci_get_drvdata(pdev);
- struct agnx_priv *priv = dev->priv;
+ struct agnx_priv *priv;
AGNX_TRACE;
if (!dev)
return;
+ priv = dev->priv;
By reverting this patch, and compile it with and without
-fno-delete-null-pointer-checks flag, we can see that the check for dev
is compiled away.
call printk #
- testq %r12, %r12 # dev
- je .L94 #,
movq %r12, %rdi # dev,
Clearly the 'fix' is to stop using dev before it is tested, but building
with -fno-delete-null-pointer-checks flag at least makes it harder to
abuse.
Signed-off-by: Eugene Teo <eugeneteo@kernel.sg>
Acked-by: Eric Paris <eparis@redhat.com>
Acked-by: Wang Cong <amwang@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This causes kernel images that don't run init to completion with certain
broken gcc versions.
This fixes kernel bugzilla entry:
http://bugzilla.kernel.org/show_bug.cgi?id=13012
I suspect the gcc problem is this:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28230
Fix the problem by using the -fno-strict-overflow flag instead, which
not only does not exist in the known-to-be-broken versions of gcc (it
was introduced later than fwrapv), but seems to be much less disturbing
to gcc too: the difference in the generated code by -fno-strict-overflow
are smaller (compared to using neither flag) than when using -fwrapv.
Reported-by: Barry K. Nathan <barryn@pobox.com>
Pushed-by: Frans Pop <elendil@planet.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Some distributions have enabled the gcc flag -Wformat-security by default.
This results in a number of warnings about format arguments to functions,
sometimes in cases where fixing the warning is not likely to actually fix a
bug. Instead of hand patching a dozens of places (possibly more) that produce
warnings that get ignored anyway we just turn off the flag in the Makefile.
Signed-off-by: Floris Kraak <randakar@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Enable the use of GCC's coverage testing tool gcov [1] with the Linux
kernel. gcov may be useful for:
* debugging (has this code been reached at all?)
* test improvement (how do I change my test to cover these lines?)
* minimizing kernel configurations (do I need this option if the
associated code is never run?)
The profiling patch incorporates the following changes:
* change kbuild to include profiling flags
* provide functions needed by profiling code
* present profiling data as files in debugfs
Note that on some architectures, enabling gcc's profiling option
"-fprofile-arcs" for the entire kernel may trigger compile/link/
run-time problems, some of which are caused by toolchain bugs and
others which require adjustment of architecture code.
For this reason profiling the entire kernel is initially restricted
to those architectures for which it is known to work without changes.
This restriction can be lifted once an architecture has been tested
and found compatible with gcc's profiling. Profiling of single files
or directories is still available on all platforms (see config help
text).
[1] http://gcc.gnu.org/onlinedocs/gcc/Gcov.html
Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Li Wei <W.Li@Sun.COM>
Cc: Michael Ellerman <michaele@au1.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Heiko Carstens <heicars2@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <mschwid2@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/sam/kbuild-next: (53 commits)
.gitignore: ignore *.lzma files
kbuild: add generic --set-str option to scripts/config
kbuild: simplify argument loop in scripts/config
kbuild: handle non-existing options in scripts/config
kallsyms: generalize text region handling
kallsyms: support kernel symbols in Blackfin on-chip memory
documentation: make version fix
kbuild: fix a compile warning
gitignore: Add GNU GLOBAL files to top .gitignore
kbuild: fix delay in setlocalversion on readonly source
README: fix misleading pointer to the defconf directory
vmlinux.lds.h update
kernel-doc: cleanup perl script
Improve vmlinux.lds.h support for arch specific linker scripts
kbuild: fix headers_exports with boolean expression
kbuild/headers_check: refine extern check
kbuild: fix "Argument list too long" error for "make headers_check",
ignore *.patch files
Remove bashisms from scripts
menu: fix embedded menu presentation
...
The GNU make's origin function know undefined variable well,
so the outer ifdef/endif conditional checking is unneeded.
From `info make` documentation, origin will return
`undefined'
if VARIABLE was never defined.
`command line'
if VARIABLE was defined on the command line.
...
Therefore, $(origin V) will get a value anyway, killing ifdef/endif is
viable and safe.
Furthermore, I've checked the minimal requirements from
Documentation/Changes is GNU make 3.79.1, and that version of GNU make
has support of origin function well already, so now it's safe to kill
the outer conditional checking, without upgrading the minimal
requirements.
Signed-off-by: Cheng Renquan <crq@kernel.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Correct the Makefile help text to read "make modules_prepare".
Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
