ARM: 7801/1: v6: prevent gcc 4.5 from reordering extended CP15 reads above is_smp...

[cascardo/linux.git] / arch / arm / include / asm / cputype.h

diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h
index 8c25dc4..9672e97 100644 (file)
--- a/arch/arm/include/asm/cputype.h
+++ b/arch/arm/include/asm/cputype.h
@@ -89,13 +89,18 @@ extern unsigned int processor_id;
                __val;                                                  \
        })
 
+/*
+ * The memory clobber prevents gcc 4.5 from reordering the mrc before
+ * any is_smp() tests, which can cause undefined instruction aborts on
+ * ARM1136 r0 due to the missing extended CP15 registers.
+ */
 #define read_cpuid_ext(ext_reg)                                                \
        ({                                                              \
                unsigned int __val;                                     \
                asm("mrc        p15, 0, %0, c0, " ext_reg               \
                    : "=r" (__val)                                      \
                    :                                                   \
-                   : "cc");                                            \
+                   : "memory");                                        \
                __val;                                                  \
        })