Commit a4d62bab authored Aug 22, 2013 by Wang Haitao Committed by Brian Norris Nov 06, 2013

mtd: map: fixed bug in 64-bit systems



Hardware:
	CPU: XLP832,the 64-bit OS
	NOR Flash:S29GL128S 128M
Software:
	Kernel:2.6.32.41
	Filesystem:JFFS2
When writing files, errors appear:
	Write len 182  but return retlen 180
	Write of 182 bytes at 0x072c815c failed. returned -5, retlen 180
	Write len 186  but return retlen 184
	Write of 186 bytes at 0x072caff4 failed. returned -5, retlen 184
These errors exist only in 64-bit systems,not in 32-bit systems. After analysis, we
found that the left shift operation is wrong in map_word_load_partial. For instance:
	unsigned char buf[3] ={0x9e,0x3a,0xea};
	map_bankwidth(map) is 4;
	for (i=0; i < 3; i++) {
		int bitpos;
		bitpos = (map_bankwidth(map)-1-i)*8;
		orig.x[0] &= ~(0xff << bitpos);
		orig.x[0] |= buf[i] << bitpos;
	}

The value of orig.x[0] is expected to be 0x9e3aeaff, but in this situation(64-bit
System) we'll get the wrong value of 0xffffffff9e3aeaff due to the 64-bit sign
extension:
buf[i] is defined as "unsigned char" and the left-shift operation will convert it
to the type of "signed int", so when left-shift buf[i] by 24 bits, the final result
will get the wrong value: 0xffffffff9e3aeaff.

If the left-shift bits are less than 24, then sign extension will not occur. Whereas
the bankwidth of the nor flash we used is 4, therefore this BUG emerges.

Signed-off-by: Pang Xunlei <pang.xunlei@zte.com.cn>
Signed-off-by: Zhang Yi <zhang.yi20@zte.com.cn>
Signed-off-by: Lu Zhongjun <lu.zhongjun@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

parent f83c3838

include/linux/mtd/map.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -365,7 +365,7 @@ static inline map_word map_word_load_partial(struct map_info *map, map_word orig
		bitpos = (map_bankwidth(map)-1-i)*8;
		#endif
		orig.x[0] &= ~(0xff << bitpos);
		orig.x[0] \|= buf[i-start] << bitpos;
		orig.x[0] \|= (unsigned long)buf[i-start] << bitpos;
		}
		}
		return orig;
		@@ -384,7 +384,7 @@ static inline map_word map_word_ff(struct map_info *map)

		if (map_bankwidth(map) < MAP_FF_LIMIT) {
		int bw = 8 * map_bankwidth(map);
		r.x[0] = (1 << bw) - 1;
		r.x[0] = (1UL << bw) - 1;
		} else {
		for (i=0; i<map_words(map); i++)
		r.x[i] = ~0UL;

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