Re: [PATCH 3/6] tracing: Wrap section comparison in tracer_alloc_buffers with COMPARE_SECTIONS

Steven Rostedt
2020-02-19T14:34:49Z

On Tue, 18 Feb 2020 21:54:20 -0700
Nathan Chancellor <natechancellor@gmail.com> wrote:

> Clang warns:
>
> ../kernel/trace/trace.c:9335:33: warning: array comparison always
> evaluates to true [-Wtautological-compare]
> if (__stop___trace_bprintk_fmt != __start___trace_bprintk_fmt)
> ^
> 1 warning generated.
>
> These are not true arrays, they are linker defined symbols, which are
> just addresses so there is not a real issue here. Use the
> COMPARE_SECTIONS macro to silence this warning by casting the linker
> defined symbols to unsigned long, which keeps the logic the same.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/765
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
> kernel/trace/trace.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index c797a15a1fc7..e1f3b16e457b 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -9332,7 +9332,7 @@ __init static int tracer_alloc_buffers(void)
> goto out_free_buffer_mask;
>
> /* Only allocate trace_printk buffers if a trace_printk exists */
> - if (__stop___trace_bprintk_fmt != __start___trace_bprintk_fmt)
> + if (COMPARE_SECTIONS(__stop___trace_bprintk_fmt, !=, __start___trace_bprintk_fmt))

Sorry, but this is really ugly and unreadable. Please find some other
solution to fix this.

NAK-by: Steven Rostedt

-- Steve

> /* Must be called before global_trace.buffer is allocated */
> trace_printk_init_buffers();
>