[PATCH] SHMLBA compat task alignment fix

From: Arun Sharma <arun.sharma@intel.com>

The current Linux implementation of shmat() insists on SHMLBA alignment even
when shmflg & SHM_RND == 0.  This is not consistent with the man pages and
the single UNIX spec, which require only a page-aligned address.

However, some architectures require a SHMLBA alignment for correctness in all
cases.  Such architectures use __ARCH_FORCE_SHMLBA.

include/asm-mips/shmparam.h

@@ -6,6 +6,8 @@
 #ifndef _ASM_SHMPARAM_H
 #define _ASM_SHMPARAM_H
 
+#define __ARCH_FORCE_SHMLBA	1
+
 #define	SHMLBA 0x40000			/* attach addr a multiple of this */
 
 #endif /* _ASM_SHMPARAM_H */

include/asm-parisc/shmparam.h

 #ifndef _ASMPARISC_SHMPARAM_H
 #define _ASMPARISC_SHMPARAM_H
 
+#define __ARCH_FORCE_SHMLBA 	1
+
 #define SHMLBA 0x00400000   /* attach addr needs to be 4 Mb aligned */
 
 #endif /* _ASMPARISC_SHMPARAM_H */

include/asm-sparc/shmparam.h

@@ -2,6 +2,8 @@
 #ifndef _ASMSPARC_SHMPARAM_H
 #define _ASMSPARC_SHMPARAM_H
 
+#define __ARCH_FORCE_SHMLBA 	1
+
 extern int vac_cache_size;
 #define SHMLBA (vac_cache_size ? vac_cache_size : \
 		(sparc_cpu_model == sun4c ? (64 * 1024) : \

include/asm-sparc64/shmparam.h

@@ -4,6 +4,7 @@
 
 #include <asm/spitfire.h>
 
+#define __ARCH_FORCE_SHMLBA	1
 /* attach addr a multiple of this */
 #define	SHMLBA	((PAGE_SIZE > L1DCACHE_SIZE) ? PAGE_SIZE : L1DCACHE_SIZE)
 

ipc/shm.c

@@ -656,7 +656,10 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
 			if (shmflg & SHM_RND)
 				addr &= ~(SHMLBA-1);	   /* round down */
 			else
-				return -EINVAL;
+#ifndef __ARCH_FORCE_SHMLBA
+				if (addr & ~PAGE_MASK)
+#endif
+					return -EINVAL;
 		}
 		flags = MAP_SHARED | MAP_FIXED;
 	} else {