[Xen-devel] [PATCH] comment fix in uaccess for x86_32

[Steven Rostedt <srostedt@xxxxxxxxxx>]

In the xen/include/asm-x86/x68_32/uaccess.h

For range_not_ok we have:

/*
 * Test whether a block of memory is a valid user space address.
 * Returns 0 if the range is valid, nonzero otherwise.
 *
 * This is equivalent to the following test:
 * (u33)addr + (u33)size >= (u33)HYPERVISOR_VIRT_START
 */
#define __range_not_ok(addr,size) ({ \
        unsigned long flag,sum; \
        asm("addl %3,%1 ; sbbl %0,%0; cmpl %1,%4; sbbl $0,%0" \
                :"=&r" (flag), "=r" (sum) \
                :"1" (addr),"g" ((int)(size)),"r" (HYPERVISOR_VIRT_START)); \
        flag; })


The code is fine, but it is *not* equivalent to >=, but it is for >.

This is not a bug in the code, since it is fine to have an address go up 
to the limit, since that just means it touches the byte before the 
limit.  But I'd figure that the comment should really reflect what it is 
doing.
Here's a simple program to prove that the comment is wrong:

----
#include <stdio.h>

#define HYPERVISOR_VIRT_START 0xFC000000UL

#define chk(addr,size) ({\
        unsigned long flag,sum; \
        asm("addl %3,%1 ; sbbl %0,%0; cmpl %1,%4; sbbl $0,%0" \
                :"=&r" (flag), "=r" (sum) \
                :"1" (addr),"g" ((int)(size)),"r" 
(HYPERVISOR_VIRT_START)); \
        flag; })

int main (int argc, char **argv)
{
        unsigned long addr;

        addr = 0xfc000000UL - 10;
        printf("chk 9 = %d\n",chk(addr,9));
        printf("chk 10 = %d\n",chk(addr,10));
        printf("chk 11 = %d\n",chk(addr,11));
        return -1;
}
----

Which produces:

chk 9 = 0
chk 10 = 0
chk 11 = -1


So I've added a patch to update the comment.

Signed-off-by: Steven Rostedt <srostedt@xxxxxxxxxx>


diff -r badf51e24549 xen/include/asm-x86/x86_32/uaccess.h
--- a/xen/include/asm-x86/x86_32/uaccess.h      Fri Oct 27 11:11:46 2006 -0400
+++ b/xen/include/asm-x86/x86_32/uaccess.h      Wed Nov 01 10:42:16 2006 -0500
@@ -8,7 +8,7 @@
  * Returns 0 if the range is valid, nonzero otherwise.
  *
  * This is equivalent to the following test:
- * (u33)addr + (u33)size >= (u33)HYPERVISOR_VIRT_START
+ * (u33)addr + (u33)size > (u33)HYPERVISOR_VIRT_START
  */
 #define __range_not_ok(addr,size) ({ \
        unsigned long flag,sum; \

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