linux-kernel - [PATCH 5/6] mm: kmemleak: Wrap section comparison in kmemleak_init with COMPARE

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Message-Id: <20200219045423.54190-6-natechancellor@gmail.com>
Date:   Tue, 18 Feb 2020 21:54:22 -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 5/6] mm: kmemleak: Wrap section comparison in kmemleak_init with COMPARE_SECTIONS

Clang warns:

../mm/kmemleak.c:1950:28: warning: array comparison always evaluates to
a constant [-Wtautological-compare]
        if (__start_ro_after_init < _sdata || __end_ro_after_init > _edata)
                                  ^
../mm/kmemleak.c:1950:60: warning: array comparison always evaluates to
a constant [-Wtautological-compare]
        if (__start_ro_after_init < _sdata || __end_ro_after_init > _edata)
                                                                  ^
2 warnings 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>
---
 mm/kmemleak.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index aa6832432d6a..e27655526ba7 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1952,7 +1952,8 @@ void __init kmemleak_init(void)
 	create_object((unsigned long)__bss_start, __bss_stop - __bss_start,
 		      KMEMLEAK_GREY, GFP_ATOMIC);
 	/* only register .data..ro_after_init if not within .data */
-	if (__start_ro_after_init < _sdata || __end_ro_after_init > _edata)
+	if (COMPARE_SECTIONS(__start_ro_after_init, <, _sdata) ||
+	    COMPARE_SECTIONS(__end_ro_after_init, >, _edata))
 		create_object((unsigned long)__start_ro_after_init,
 			      __end_ro_after_init - __start_ro_after_init,
 			      KMEMLEAK_GREY, GFP_ATOMIC);
-- 
2.25.1