linux-kernel - [PATCH 5/5] asm-generic: fix build error in fix_to_virt with CONFIG_DEBUG

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Date:   Tue,  1 May 2018 21:00:14 +0800
From:   changbin.du@...el.com
To:     yamada.masahiro@...ionext.com, michal.lkml@...kovi.net,
        tglx@...utronix.de, mingo@...hat.com, akpm@...ux-foundation.org
Cc:     x86@...nel.org, lgirdwood@...il.com, broonie@...nel.org,
        arnd@...db.de, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Changbin Du <changbin.du@...el.com>
Subject: [PATCH 5/5] asm-generic: fix build error in fix_to_virt with CONFIG_DEBUG_EXPERIENCE

From: Changbin Du <changbin.du@...el.com>

With '-Og' optimization level, GCC would not optimize a count for a loop
as a constant value. But BUILD_BUG_ON() only accept compile-time constant
values.

arch/arm/mm/mmu.o: In function `fix_to_virt':
/home/changbin/work/linux/./include/asm-generic/fixmap.h:31: undefined reference to `__compiletime_assert_31'
Makefile:1051: recipe for target 'vmlinux' failed
make: *** [vmlinux] Error 1

Signed-off-by: Changbin Du <changbin.du@...el.com>
---
 include/asm-generic/fixmap.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/fixmap.h b/include/asm-generic/fixmap.h
index 827e4d3..a6576d4 100644
--- a/include/asm-generic/fixmap.h
+++ b/include/asm-generic/fixmap.h
@@ -28,7 +28,8 @@
  */
 static __always_inline unsigned long fix_to_virt(const unsigned int idx)
 {
-	BUILD_BUG_ON(idx >= __end_of_fixed_addresses);
+	BUILD_BUG_ON(__builtin_constant_p(idx) &&
+		     idx >= __end_of_fixed_addresses);
 	return __fix_to_virt(idx);
 }
 
-- 
2.7.4