linux-kernel - [PATCH 3/6] tracing: Wrap section comparison in tracer_alloc_buffers with COMPARE

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Message-Id: <20200219045423.54190-4-natechancellor@gmail.com>
Date:   Tue, 18 Feb 2020 21:54:20 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Arnd Bergmann <arnd@...db.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH 3/6] tracing: Wrap section comparison in tracer_alloc_buffers with COMPARE_SECTIONS

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@...il.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))
 		/* Must be called before global_trace.buffer is allocated */
 		trace_printk_init_buffers();
 
-- 
2.25.1