linux-kernel - [PATCH 1/3] spi: fix undefined behaviour in SPI_BPW_RANGE

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Message-Id: <1369929581-30258-1-git-send-email-swarren@wwwdotorg.org>
Date:	Thu, 30 May 2013 09:59:39 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Mark Brown <broonie@...nel.org>,
	Grant Likely <grant.likely@...aro.org>
Cc:	linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Stephen Warren <swarren@...dia.com>
Subject: [PATCH 1/3] spi: fix undefined behaviour in SPI_BPW_RANGE_MASK

From: Stephen Warren <swarren@...dia.com>

The parameters to SPI_BPW_RANGE_MASK() are in the range 1..32. If 32 is
used as a parameter, part of the expression is "1 << 32". Since 32 is >=
the size of the type in use, such a shift is undefined behaviour. Add
macro SPI_BIT_MASK to Implement a special case and thus avoid undefined
behaviour. Use this new macro rather than BIT() when implementing
SPI_BPW_RANGE_MASK().

This fixes build warnings such as:
drivers/spi/spi-gpio.c:446:2: warning: left shift count >= width of type [enabled by default]

SPI_BPW_MASK() already avoids this, since its parameter is also in range
1..32, yet it only shifts by up to one less than the input parameter.

Reported-by: Fengguang Wu <fengguang.wu@...el.com>
Signed-off-by: Stephen Warren <swarren@...dia.com>
---
 include/linux/spi/spi.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 1737256..3e94791 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -309,7 +309,8 @@ struct spi_master {
 	/* bitmask of supported bits_per_word for transfers */
 	u32			bits_per_word_mask;
 #define SPI_BPW_MASK(bits) BIT((bits) - 1)
-#define SPI_BPW_RANGE_MASK(min, max) ((BIT(max) - 1) - (BIT(min) - 1))
+#define SPI_BIT_MASK(bits) (((bits) == 32) ? ~0UL : (BIT(bits) - 1))
+#define SPI_BPW_RANGE_MASK(min, max) (SPI_BIT_MASK(max) - SPI_BIT_MASK(min))
 
 	/* other constraints relevant to this driver */
 	u16			flags;
-- 
1.7.10.4

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