From: David Laight
> Sent: 23 October 2020 22:52
...
> Could do_put_user() do an initial check for 64 bit
> then expand a different #define that contains the actual
> code passing either "a" or "A" for the constriant.
>
> Apart from another level of indirection nothing is duplicated.
This code seems to compile to something sensible.
It does need change the registers that get_user_n() must
use - the normal return value is now in %ax (and %dx for
64bit values on 32bit systems, with the error in %cx.
(I've not actually tested it.)
#define __inttype_max(x, _max) __typeof__( \
__typefits(x,char, \
__typefits(x,short, \
__typefits(x,int, \
__typefits(x,long,_max)))))
#define __inttype(x) __inttype_max(x, 0ULL)
#define get_user_1(x, ptr, type, constraint) \
({ \
int __ret_gu; \
type __val_gu; \
asm volatile("call __get_user_%P4" \
: "=c" (__ret_gu), constraint (__val_gu), \
ASM_CALL_CONSTRAINT \
: "a" (ptr), "i" (sizeof(*(ptr)))); \
(x) = (__force __typeof__(*(ptr))) __val_gu; \
__builtin_expect(__ret_gu, 0); \
})
#define get_user(x, ptr) \
({ \
__chk_user_ptr(ptr); \
might_fault(); \
(sizeof *(ptr) > sizeof(long)) \
? get_user_1(x, ptr, long long, "=A") \
: get_user_1(x, ptr, __inttype_max(*(ptr),0ul), "=a"); \
})
The __inttype_max() is needed (I think) because clang will try (and fail)
to generate the asm for 64bit values on 32bit systems.
So the type needs limiting to 32bits.
Always using 'long' works - but generates extra casts.
The "=A" constraint (%rax or %rdx) is never used on 64bit because
the test is always false.
David
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UK
Registration No: 1397386 (Wales)
