From: Steven Rostedt Date: Thu, 8 Sep 2016 12:34:33 -0400 Subject: [PATCH] lockdep: Quiet gcc about dangerous __builtin_return_address() operations Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.8/older/patches-4.8.14-rt9.tar.xz [ Boris, does this quiet gcc for you? I haven't fully tested this yet, as I still don't have a compiler that does the warning. ] Gcc's new warnings about __builtin_return_address(n) operations with n > 0 is popping up around the kernel. The operation is dangerous, and the warning is "good to know". But there's instances that we use __builtin_return_address(n) with n > 0 and are aware of the issues, and work around them. And its used mostly for tracing and debugging. In these cases, the warning becomes a distraction and is not helpful. To get better lock issue traces, a function like get_lock_parent_ip() uses __builtin_return_address() to find the caller of the lock, and skip over the internal callers of the lock itself. Currently it is only used in the kernel/ directory and only if certain configs are enabled. Create a new config called CONFIG_USING_GET_LOCK_PARENT_IP that gets selected when another config relies on get_lock_parent_ip(), and this will now enable the function get_lock_parent_ip(), otherwise it wont be defined. It will also disable the frame-address warnings from gcc in the kernel directory. Reported-by: Borislav Petkov Signed-off-by: Steven Rostedt --- include/linux/ftrace.h | 2 ++ kernel/Makefile | 7 +++++++ kernel/trace/Kconfig | 1 + lib/Kconfig.debug | 10 ++++++++++ 4 files changed, 20 insertions(+) --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -714,6 +714,7 @@ static inline void __ftrace_enabled_rest #define CALLER_ADDR5 ((unsigned long)ftrace_return_address(5)) #define CALLER_ADDR6 ((unsigned long)ftrace_return_address(6)) +#ifdef CONFIG_USING_GET_LOCK_PARENT_IP static inline unsigned long get_lock_parent_ip(void) { unsigned long addr = CALLER_ADDR0; @@ -725,6 +726,7 @@ static inline unsigned long get_lock_par return addr; return CALLER_ADDR2; } +#endif #ifdef CONFIG_IRQSOFF_TRACER extern void time_hardirqs_on(unsigned long a0, unsigned long a1); --- a/kernel/Makefile +++ b/kernel/Makefile @@ -11,6 +11,13 @@ obj-y = fork.o exec_domain.o panic.o notifier.o ksysfs.o cred.o reboot.o \ async.o range.o smpboot.o +# Tracing may do some dangerous __builtin_return_address() operations +# We know they are dangerous, we don't need gcc telling us that. +ifdef CONFIG_USING_GET_LOCK_PARENT_IP +FRAME_CFLAGS := $(call cc-disable-warning,frame-address) +KBUILD_CFLAGS += $(FRAME_CFLAGS) +endif + obj-$(CONFIG_MULTIUSER) += groups.o ifdef CONFIG_FUNCTION_TRACER --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -197,6 +197,7 @@ config PREEMPT_TRACER select RING_BUFFER_ALLOW_SWAP select TRACER_SNAPSHOT select TRACER_SNAPSHOT_PER_CPU_SWAP + select USING_GET_LOCK_PARENT_IP help This option measures the time spent in preemption-off critical sections, with microsecond accuracy. --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -977,6 +977,7 @@ config TIMER_STATS config DEBUG_PREEMPT bool "Debug preemptible kernel" depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT + select USING_GET_LOCK_PARENT_IP default y help If you say Y here then the kernel will use a debug variant of the @@ -1159,8 +1160,17 @@ config LOCK_TORTURE_TEST endmenu # lock debugging +config USING_GET_LOCK_PARENT_IP + bool + help + Enables the use of the function get_lock_parent_ip() that + will use __builtin_return_address(n) with n > 0 causing + some gcc warnings. When this is selected, those warnings + will be suppressed. + config TRACE_IRQFLAGS bool + select USING_GET_LOCK_PARENT_IP help Enables hooks to interrupt enabling and disabling for either tracing or lock debugging.