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From a3ca86aea507904148870946d599e07a340b39bf Mon Sep 17 00:00:00 2001
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From: Eugene Teo <eteo@redhat.com>
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Date: Wed, 15 Jul 2009 14:59:10 +0800
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Subject: Add '-fno-delete-null-pointer-checks' to gcc CFLAGS
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From: Eugene Teo <eteo@redhat.com>
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commit a3ca86aea507904148870946d599e07a340b39bf upstream.
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Turning on this flag could prevent the compiler from optimising away
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some "useless" checks for null pointers. Such bugs can sometimes become
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exploitable at compile time because of the -O2 optimisation.
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See http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Optimize-Options.html
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An example that clearly shows this 'problem' is commit 6bf67672.
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static void __devexit agnx_pci_remove(struct pci_dev *pdev)
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{
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struct ieee80211_hw *dev = pci_get_drvdata(pdev);
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- struct agnx_priv *priv = dev->priv;
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+ struct agnx_priv *priv;
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AGNX_TRACE;
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if (!dev)
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return;
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+ priv = dev->priv;
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By reverting this patch, and compile it with and without
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-fno-delete-null-pointer-checks flag, we can see that the check for dev
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is compiled away.
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call printk #
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- testq %r12, %r12 # dev
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- je .L94 #,
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movq %r12, %rdi # dev,
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Clearly the 'fix' is to stop using dev before it is tested, but building
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with -fno-delete-null-pointer-checks flag at least makes it harder to
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abuse.
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Signed-off-by: Eugene Teo <eugeneteo@kernel.sg>
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Acked-by: Eric Paris <eparis@redhat.com>
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Acked-by: Wang Cong <amwang@redhat.com>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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---
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Makefile | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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--- a/Makefile
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+++ b/Makefile
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@@ -340,7 +340,8 @@ KBUILD_CPPFLAGS := -D__KERNEL__ $(LINUXI
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KBUILD_CFLAGS := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
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-fno-strict-aliasing -fno-common \
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- -Werror-implicit-function-declaration
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+ -Werror-implicit-function-declaration \
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+ -fno-delete-null-pointer-checks
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KBUILD_AFLAGS := -D__ASSEMBLY__
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# Read KERNELRELEASE from include/config/kernel.release (if it exists)
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