Add "memory" clobbers to the x86 inline asm of strncmp and friends

They don't actually clobber memory, but gcc doesn't even know they
_read_ memory, so can apparently re-order memory accesses around them.

Which obviously does the wrong thing if the memory access happens to
change the memory that the compare function is accessing..

Verified to fix a strange boot problem by Jens Axboe.

diff --git a/include/asm-i386/string.h b/include/asm-i386/string.h
index 6a78ac5..02c8f5d 100644 (file)
--- a/include/asm-i386/string.h
+++ b/include/asm-i386/string.h
@@ -116,7 +116,8 @@ __asm__ __volatile__(
        "orb $1,%%al\n"
        "3:"
        :"=a" (__res), "=&S" (d0), "=&D" (d1)
-                    :"1" (cs),"2" (ct));
+       :"1" (cs),"2" (ct)
+       :"memory");
 return __res;
 }
 
@@ -138,8 +139,9 @@ __asm__ __volatile__(
        "3:\tsbbl %%eax,%%eax\n\t"
        "orb $1,%%al\n"
        "4:"
-                    :"=a" (__res), "=&S" (d0), "=&D" (d1), "=&c" (d2)
-                    :"1" (cs),"2" (ct),"3" (count));
+       :"=a" (__res), "=&S" (d0), "=&D" (d1), "=&c" (d2)
+       :"1" (cs),"2" (ct),"3" (count)
+       :"memory");
 return __res;
 }
 
@@ -158,7 +160,9 @@ __asm__ __volatile__(
        "movl $1,%1\n"
        "2:\tmovl %1,%0\n\t"
        "decl %0"
-       :"=a" (__res), "=&S" (d0) : "1" (s),"0" (c));
+       :"=a" (__res), "=&S" (d0)
+       :"1" (s),"0" (c)
+       :"memory");
 return __res;
 }
 
@@ -175,7 +179,9 @@ __asm__ __volatile__(
        "leal -1(%%esi),%0\n"
        "2:\ttestb %%al,%%al\n\t"
        "jne 1b"
-       :"=g" (__res), "=&S" (d0), "=&a" (d1) :"0" (0),"1" (s),"2" (c));
+       :"=g" (__res), "=&S" (d0), "=&a" (d1)
+       :"0" (0),"1" (s),"2" (c)
+       :"memory");
 return __res;
 }
 
@@ -189,7 +195,9 @@ __asm__ __volatile__(
        "scasb\n\t"
        "notl %0\n\t"
        "decl %0"
-       :"=c" (__res), "=&D" (d0) :"1" (s),"a" (0), "0" (0xffffffffu));
+       :"=c" (__res), "=&D" (d0)
+       :"1" (s),"a" (0), "0" (0xffffffffu)
+       :"memory");
 return __res;
 }
 
@@ -333,7 +341,9 @@ __asm__ __volatile__(
        "je 1f\n\t"
        "movl $1,%0\n"
        "1:\tdecl %0"
-       :"=D" (__res), "=&c" (d0) : "a" (c),"0" (cs),"1" (count));
+       :"=D" (__res), "=&c" (d0)
+       :"a" (c),"0" (cs),"1" (count)
+       :"memory");
 return __res;
 }
 
@@ -369,7 +379,7 @@ __asm__ __volatile__(
        "je 2f\n\t"
        "stosb\n"
        "2:"
-       : "=&c" (d0), "=&D" (d1)
+       :"=&c" (d0), "=&D" (d1)
        :"a" (c), "q" (count), "0" (count/4), "1" ((long) s)
        :"memory");
 return (s);    
@@ -392,7 +402,8 @@ __asm__ __volatile__(
        "jne 1b\n"
        "3:\tsubl %2,%0"
        :"=a" (__res), "=&d" (d0)
-       :"c" (s),"1" (count));
+       :"c" (s),"1" (count)
+       :"memory");
 return __res;
 }
 /* end of additional stuff */
@@ -473,7 +484,8 @@ static inline void * memscan(void * addr, int c, size_t size)
                "dec %%edi\n"
                "1:"
                : "=D" (addr), "=c" (size)
-               : "0" (addr), "1" (size), "a" (c));
+               : "0" (addr), "1" (size), "a" (c)
+               : "memory");
        return addr;
 }