Patch "Disable "frame-address" warning" has been added to the 4.4-stable tree
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This is a note to let you know that I've just added the patch titled
Disable "frame-address" warning
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
disable-frame-address-warning.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.
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124a3d88fa20e1869fc229d7d8c740cc81944264Mon Sep 17 00:00:00 2001
From: Linus Torvalds <[email protected]>
Date: Wed, 27 Jul 2016 19:03:04 -0700
Subject: Disable "frame-address" warning
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From: Linus Torvalds <[email protected]>
commit 124a3d88fa20e1869fc229d7d8c740cc81944264 upstream.
Newer versions of gcc warn about the use of __builtin_return_address() with a non-zero argument when "-Wall" is specified:
kernel/trace/trace_irqsoff.c: In function ‘stop_critical_timings’:
kernel/trace/trace_irqsoff.c:433:86: warning: calling ‘__builtin_return_address’ with a nonzero argument is unsafe [-Wframe-address]
stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
[ .. repeats a few times for other similar cases .. ]
It is true that a non-zero argument is somewhat dangerous, and we do not actually have very many uses of that in the kernel - but the ftrace code does use it, and as Stephen Rostedt says:
"We are well aware of the danger of using __builtin_return_address() of
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0. In fact that's part of the reason for having the "thunk" code in
x86 (See arch/x86/entry/thunk_{64,32}.S). [..] it adds extra frames when tracking irqs off sections, to prevent __builtin_return_address() from accessing bad areas. In fact the thunk_32.S states: 'Trampoline to trace irqs off. (otherwise CALLER_ADDR1 might crash)'."
For now, __builtin_return_address() with a non-zero argument is the best we can do, and the warning is not helpful and can end up making people miss other warnings for real problems.
So disable the frame-address warning on compilers that need it.
--- Makefile | 1 + 1 file changed, 1 insertion(+)
Makefile +1 -0
@@ -617,6 +617,7 @@ include arch/$(SRCARCH)/Makefile KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) KBUILD_CFLAGS += $(call cc-disable-warning,maybe-uninitialized,) +KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,) ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os
Patches currently in stable-queue which might be from [email protected] are
queue-4.4/mm-list_lru.c-avoid-error-path-null-pointer-deref.patch queue-4.4/mm-memcontrol-do-not-recurse-in-direct-reclaim.patch queue-4.4/disable-frame-address-warning.patch queue-4.4/x86-xen-fix-upper-bound-of-pmd-loop-in-xen_cleanhighmap.patch queue-4.4/mm-cma-silence-warnings-due-to-max-usage.patch queue-4.4/h8300-fix-syscall-restarting.patch queue-4.4/fix-potential-infoleak-in-older-kernels.patch