From: Linus Torvalds <torvalds@ppc970.osdl.org>
Date: Fri, 24 Jun 2005 17:39:17 +0000 (-0700)
Subject: Add "memory" clobbers to the x86 inline asm of strncmp and friends
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=793ae77469121227cd910c4b99f24be1de34bcca;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git

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 6a78ac58c194..02c8f5d22065 100644
--- 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;
 }