Re: [PATCH] kernel/kcov.c: mark func write_comp_data() as notrace

From: Steven Rostedt <rostedt@goodmis.org>
To: Anders Roxell <anders.roxell@linaro.org>
Cc: akpm@linux-foundation.org, will.deacon@arm.com,
	linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH] kernel/kcov.c: mark func write_comp_data() as notrace
Date: Thu, 6 Dec 2018 13:14:17 -0500	[thread overview]
Message-ID: <20181206131417.5019b1e8@vmware.local.home> (raw)
In-Reply-To: <20181206143011.23719-1-anders.roxell@linaro.org>

On Thu,  6 Dec 2018 15:30:11 +0100
Anders Roxell <anders.roxell@linaro.org> wrote:

> Since __sanitizer_cov_trace_const_cmp4 is marked as notrace, the
> function called from __sanitizer_cov_trace_const_cmp4 shouldn't be
> traceable either.  ftrace_graph_caller() gets called every time func
> write_comp_data() gets called if it isn't marked 'notrace'. This is the
> backtrace from gdb:
> 
>  #0  ftrace_graph_caller () at ../arch/arm64/kernel/entry-ftrace.S:179
>  #1  0xffffff8010201920 in ftrace_caller () at ../arch/arm64/kernel/entry-ftrace.S:151
>  #2  0xffffff8010439714 in write_comp_data (type=5, arg1=0, arg2=0, ip=18446743524224276596) at ../kernel/kcov.c:116
>  #3  0xffffff8010439894 in __sanitizer_cov_trace_const_cmp4 (arg1=<optimized out>, arg2=<optimized out>) at ../kernel/kcov.c:188
>  #4  0xffffff8010201874 in prepare_ftrace_return (self_addr=18446743524226602768, parent=0xffffff801014b918, frame_pointer=18446743524223531344) at ./include/generated/atomic-instrumented.h:27
>  #5  0xffffff801020194c in ftrace_graph_caller () at ../arch/arm64/kernel/entry-ftrace.S:182
> 
> Rework so that write_comp_data() that are called from
> __sanitizer_cov_trace_*_cmp*() are marked as 'notrace'.
> 
> Commit 903e8ff86753 ("kernel/kcov.c: mark funcs in __sanitizer_cov_trace_pc() as notrace")
> missed to mark write_comp_data() as 'notrace'. When that patch was
> created gcc-7 was used. In lib/Kconfig.debug
> config KCOV_ENABLE_COMPARISONS
> 	depends on $(cc-option,-fsanitize-coverage=trace-cmp)
> 
> That code path isn't hit with gcc-7. However, it were that with gcc-8.
> 
> Co-developed-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Anders Roxell <anders.roxell@linaro.org>

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

> ---
>  kernel/kcov.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 97959d7b77e2..c2277dbdbfb1 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -112,7 +112,7 @@ void notrace __sanitizer_cov_trace_pc(void)
>  EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
>  
>  #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
> -static void write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
> +static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
>  {
>  	struct task_struct *t;
>  	u64 *area;