On Thu, Feb 04, 2016 at 09:08:22AM -0500, Benjamin LaHaise wrote:
> On Thu, Feb 04, 2016 at 01:50:56PM +0000, Russell King - ARM Linux wrote:
> > > I am still convinced that this is an architecture issue. Given that 64 bit
> > > values work in the *get_user implementations on other architectures, I see
> > > no reason there should need to be a workaround for this in common code.
> >
> > So you're happy to break x86-32 then...
>
> x86-32 works fine.
Let me repeat the quote from my previous email:
#define __get_user(x, ptr) \
__get_user_nocheck((x), (ptr), sizeof(*(ptr)))
#define __get_user_nocheck(x, ptr, size) \
({ \
int __gu_err; \
unsigned long __gu_val; \
__uaccess_begin(); \
__get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT); \
__uaccess_end(); \
(x) = (__force __typeof__(*(ptr)))__gu_val; \
__builtin_expect(__gu_err, 0); \
})
#define __get_user_size(x, ptr, size, retval, errret) \
do { \
retval = 0; \
__chk_user_ptr(ptr); \
switch (size) { \
case 1: \
__get_user_asm(x, ptr, retval, "b", "b", "=q", errret); \
break; \
case 2: \
__get_user_asm(x, ptr, retval, "w", "w", "=r", errret); \
break; \
case 4: \
__get_user_asm(x, ptr, retval, "l", "k", "=r", errret); \
break; \
case 8: \
__get_user_asm_u64(x, ptr, retval, errret); \
break; \
default: \
(x) = __get_user_bad(); \
} \
} while (0)
#ifdef CONFIG_X86_32
#define __get_user_asm_u64(x, ptr, retval, errret) (x) = __get_user_bad()
#define __get_user_asm_ex_u64(x, ptr) (x) = __get_user_bad()
#else
#define __get_user_asm_u64(x, ptr, retval, errret) \
__get_user_asm(x, ptr, retval, "q", "", "=r", errret)
#define __get_user_asm_ex_u64(x, ptr) \
__get_user_asm_ex(x, ptr, "q", "", "=r")
#endif
Hence, __get_user() on x86-32 with a 64-bit quantity results in
__get_user_bad() being called, which is an undefined function.
Only if you build with x86-64 support enabled (iow, CONFIG_X86_32 not
defined) then you get the 64-bit __get_user() support.
Given this, I fail to see how x86-32 can possibly work.
--
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