linux-kernel - [PATCH v2 2/3] lib/vsprintf.c: move sizeof(struct printf

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Date:   Fri,  8 Feb 2019 21:30:14 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        linux-kernel@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH v2 2/3] lib/vsprintf.c: move sizeof(struct printf_spec) next to its definition

At the time of d0484193 (lib/vsprintf.c: expand field_width to 24
bits), there was no compiletime_assert/BUILD_BUG/.... variant that
could be used outside function scope. Now we have static_assert(), so
move the assertion next to the definition instead of hiding it in some
arbitrary function.

Also add the appropriate #include to avoid relying on build_bug.h
being pulled in via some arbitrary chain of includes.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
v2: added, mostly as an example of use of static_assert(), to check
that the compiler actually groks it.

 lib/vsprintf.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3add92329bae..30b00de4f321 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -17,6 +17,7 @@
  */
 
 #include <stdarg.h>
+#include <linux/build_bug.h>
 #include <linux/clk.h>
 #include <linux/clk-provider.h>
 #include <linux/module.h>	/* for KSYM_SYMBOL_LEN */
@@ -405,6 +406,8 @@ struct printf_spec {
 	unsigned int	base:8;		/* number base, 8, 10 or 16 only */
 	signed int	precision:16;	/* # of digits/chars */
 } __packed;
+static_assert(sizeof(struct printf_spec) == 8);
+
 #define FIELD_WIDTH_MAX ((1 << 23) - 1)
 #define PRECISION_MAX ((1 << 15) - 1)
 
@@ -422,8 +425,6 @@ char *number(char *buf, char *end, unsigned long long num,
 	int field_width = spec.field_width;
 	int precision = spec.precision;
 
-	BUILD_BUG_ON(sizeof(struct printf_spec) != 8);
-
 	/* locase = 0 or 0x20. ORing digits or letters with 'locase'
 	 * produces same digits or (maybe lowercased) letters */
 	locase = (spec.flags & SMALL);
-- 
2.20.1