Messages in this thread | | | Date | Wed, 14 Jul 2010 17:55:40 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH] x86: fix ordering constraints on crX read/writes |
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On 07/14/2010 05:28 PM, Zachary Amsden wrote: > >> static inline void native_write_cr2(unsigned long val) >> { >> - asm volatile("mov %0,%%cr2": : "r" (val), "m" (__force_order)); >> + asm volatile("mov %1,%%cr2": "+m" (__force_order) : "r" (val) : >> "memory"); >> } >> > > > You don't need the memory clobber there. Technically, this should > never be used, however.
Yes. I just did it for consistency. Likewise, I didn't pore over the manuals to work out whether writes to any crX could really have memory side-effects.
>> >> static inline unsigned long native_read_cr3(void) >> { >> unsigned long val; >> - asm volatile("mov %%cr3,%0\n\t" : "=r" (val), "=m" >> (__force_order)); >> + asm volatile("mov %%cr3,%0\n\t" : "=r" (val) : "m" >> (__force_order)); >> return val; >> } >> >> static inline void native_write_cr3(unsigned long val) >> { >> - asm volatile("mov %0,%%cr3": : "r" (val), "m" (__force_order)); >> + asm volatile("mov %1,%%cr3": "+m" (__force_order) : "r" (val) : >> "memory"); >> } >> >> static inline unsigned long native_read_cr4(void) >> { >> unsigned long val; >> - asm volatile("mov %%cr4,%0\n\t" : "=r" (val), "=m" >> (__force_order)); >> + asm volatile("mov %%cr4,%0\n\t" : "=r" (val) : "m" >> (__force_order)); >> return val; >> } >> >> @@ -271,7 +286,7 @@ static inline unsigned long >> native_read_cr4_safe(void) >> asm volatile("1: mov %%cr4, %0\n" >> "2:\n" >> _ASM_EXTABLE(1b, 2b) >> - : "=r" (val), "=m" (__force_order) : "0" (0)); >> + : "=r" (val) : "m" (__force_order), "0" (0)); >> #else >> val = native_read_cr4(); >> #endif >> @@ -280,7 +295,7 @@ static inline unsigned long >> native_read_cr4_safe(void) >> >> static inline void native_write_cr4(unsigned long val) >> { >> - asm volatile("mov %0,%%cr4": : "r" (val), "m" (__force_order)); >> + asm volatile("mov %1,%%cr4": "+m" (__force_order) : "r" (val) : >> "memory"); >> } >> >> #ifdef CONFIG_X86_64 >> >> >> > > Looks good. I really hope __force_order gets pruned however. Does it > actually?
There's a couple of instances in my vmlinux. I didn't try to track them back to specific .o files. gcc tends to generate references by putting its address into a register and passing that into the asms.
J
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