x86: mark read_crX() asm code as volatile
Some gcc versions (I checked at least 4.1.1 from RHEL5 & 4.1.2 from gentoo)
can generate incorrect code with read_crX()/write_crX() functions mix up,
due to cached results of read_crX().
The small app for x8664 below compiled with -O2 demonstrates this
(i686 does the same thing):
diff --git a/include/asm-x86/system_32.h b/include/asm-x86/system_32.h
index d84e593..1d6fb3a 100644
--- a/include/asm-x86/system_32.h
+++ b/include/asm-x86/system_32.h
@@ -142,7 +142,7 @@
{
unsigned long val;
/* This could fault if %cr4 does not exist */
- asm("1: movl %%cr4, %0 \n"
+ asm volatile("1: movl %%cr4, %0 \n"
"2: \n"
".section __ex_table,\"a\" \n"
".long 1b,2b \n"