From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
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
> 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.
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
Makefile | 1 +
1 file changed, 1 insertion(+)
diff --git a/Makefile b/Makefile
index 39bfb82f7106..56ad5978a4e7 100644
--- a/Makefile
+++ b/Makefile
@@ -583,6 +583,7 @@ endif # $(dot-config)
all: vmlinux
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
--
2.10.1
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