Re: [ros-dev] [ros-diffs] [tfaber] 62266: [CRT] - Force the use of memory operands in bit test intrinsics. Bit offsets above 31 (or 63) can't behave correctly with registers (the constant case is fine because it ensures low...

[Timo Kreuzer]

While the bug was definately on our side, I still think there is a
GCC/CLANG bug here as well. Memory operands larger than register size
are a rare case (probably limited to the bittest instructions) but
allowing a register operand here should cause the compiler to either
error out or in the worst case emit something like "mov eax,
[BaseAddress]; bt eax, cl;" or "mov eax, [PointerToBaseAddress]; mov
eax, [eax]; bt eax, cl;" rather than "bt [PointerToBaseAddress], cl;",
which it actually did. Changing the constraint to something that wasn't
working changed the behaviour in a way that changed the level of
dereference! The operation was done on the pointer instead of on the
memory pointed to by the pointer!
Maybe we should file a bugreport.

Am 20.02.2014 20:28, schrieb [e-mail]:
> Author: tfaber
> Date: Thu Feb 20 19:28:27 2014
> New Revision: 62266
>
> URL: http://svn.reactos.org/svn/reactos?rev=62266&view=rev
> Log:
> [CRT]
> Force the use of memory operands in bit test intrinsics. Bit offsets above 31 (or 63) can't behave correctly with registers (the constant case is fine because it ensures low offsets). Thanks to Timo Kreuzer and Alex Radocea.
>
> Modified:
>     trunk/reactos/include/crt/mingw32/intrin_x86.h
>
> Modified: trunk/reactos/include/crt/mingw32/intrin_x86.h
> URL: http://svn.reactos.org/svn/reactos/trunk/reactos/include/crt/mingw32/intrin_...
> ==============================================================================
> --- trunk/reactos/include/crt/mingw32/intrin_x86.h	[iso-8859-1] (original)
> +++ trunk/reactos/include/crt/mingw32/intrin_x86.h	[iso-8859-1] Thu Feb 20 19:28:27 2014
> @@ -1032,7 +1032,7 @@
>    if(__builtin_constant_p(b))
>    	__asm__("bt %[b], %[a]; setb %b[retval]" : [retval] "=q" (retval) : [a] "mr" (*(a + (b / 32))), [b] "Ir" (b % 32));
>    else
> __asm__("bt %[b], %[a]; setb %b[retval]" : [retval] "=q" (retval) : [a] "mr" (*a), [b] "r" (b));
> __asm__("bt %[b], %[a]; setb %b[retval]" : [retval] "=q" (retval) : [a] "m" (*a), [b] "r" (b));
>
> return retval;
>
> }
> @@ -1045,7 +1045,7 @@
>    if(__builtin_constant_p(b))
>    	__asm__("bt %[b], %[a]; setb %b[retval]" : [retval] "=q" (retval) : [a] "mr" (*(a + (b / 64))), [b] "Ir" (b % 64));
>    else
> __asm__("bt %[b], %[a]; setb %b[retval]" : [retval] "=q" (retval) : [a] "mr" (*a), [b] "r" (b));
> __asm__("bt %[b], %[a]; setb %b[retval]" : [retval] "=q" (retval) : [a] "m" (*a), [b] "r" (b));
>
> return retval;
>
> }
> @@ -1058,7 +1058,7 @@
>    if(__builtin_constant_p(b))
>    	__asm__("btc %[b], %[a]; setb %b[retval]" : [a] "+mr" (*(a + (b / 32))), [retval] "=q" (retval) : [b] "Ir" (b % 32));
>    else
> __asm__("btc %[b], %[a]; setb %b[retval]" : [a] "+mr" (*a), [retval] "=q" (retval) : [b] "r" (b));
> __asm__("btc %[b], %[a]; setb %b[retval]" : [a] "+m" (*a), [retval] "=q" (retval) : [b] "r" (b));
>
> return retval;
>
> }
> @@ -1070,7 +1070,7 @@
>    if(__builtin_constant_p(b))
>    	__asm__("btr %[b], %[a]; setb %b[retval]" : [a] "+mr" (*(a + (b / 32))), [retval] "=q" (retval) : [b] "Ir" (b % 32));
>    else
> __asm__("btr %[b], %[a]; setb %b[retval]" : [a] "+mr" (*a), [retval] "=q" (retval) : [b] "r" (b));
> __asm__("btr %[b], %[a]; setb %b[retval]" : [a] "+m" (*a), [retval] "=q" (retval) : [b] "r" (b));
>
> return retval;
>
> }
> @@ -1082,7 +1082,7 @@
>    if(__builtin_constant_p(b))
>    	__asm__("bts %[b], %[a]; setb %b[retval]" : [a] "+mr" (*(a + (b / 32))), [retval] "=q" (retval) : [b] "Ir" (b % 32));
>    else
> __asm__("bts %[b], %[a]; setb %b[retval]" : [a] "+mr" (*a), [retval] "=q" (retval) : [b] "r" (b));
> __asm__("bts %[b], %[a]; setb %b[retval]" : [a] "+m" (*a), [retval] "=q" (retval) : [b] "r" (b));
>
> return retval;
>
> }