llvm dev - Feb 2010 - [LLVMdev] FD_ZERO unsupported inline asm on 64 bit

Hello,

I get this error when compiling this code with llvm-gcc:
error: unsupported inline asm: input constraint with a matching output
constraint of incompatible type!

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

int 
main(void)
{
	fd_set rfds;
	FD_ZERO(&rfds);   //this is the error line
	return 0;
}

I used llvm-2.6 compiled from source and the latest llvm-gcc binaries for Linux
x86_64.
This code worked just fine with older versions of llvm-gcc on 32 bit Linux. 

FD_ZERO is defined in /usr/include/bits/select.h like this:

# if __WORDSIZE == 64
#  define __FD_ZERO_STOS "stosq"
#  define __FD_SET_BTS "btsq"
#  define __FD_CLR_BTR "btrq"
#  define __FD_ISSET_BT "btq"
# else
#  define __FD_ZERO_STOS "stosl"
#  define __FD_SET_BTS "btsl"
#  define __FD_CLR_BTR "btrl"
#  define __FD_ISSET_BT "btl"
# endif

# define __FD_ZERO(fdsp) \
  do {                                                                        \
    int __d0, __d1;                                                           \
    __asm__ __volatile__ ("cld; rep; " __FD_ZERO_STOS                 
\
                          : "=c" (__d0), "=D" (__d1)        
\
                          : "a" (0), "0" (sizeof (fd_set)   
\
                                          / sizeof (__fd_mask)),              \
                            "1" (&__FDS_BITS (fdsp)[0])           
\
                          : "memory");                                
\
  } while (0)

Thanks, 
Cristi

Hi Cristian, this is (part of) bug 3373, see
   http://llvm.org/bugs/show_bug.cgi?id=3373
> 	FD_ZERO(&rfds);   //this is the error line
...
> # define __FD_ZERO(fdsp) \
>   do {                                                                     
\
>     int __d0, __d1;                                                        
\
>     __asm__ __volatile__ ("cld; rep; " __FD_ZERO_STOS            
\
>                           : "=c" (__d0), "=D" (__d1)   
\
>                           : "a" (0), "0" (sizeof
(fd_set)                     \
>                                           / sizeof (__fd_mask)),           
\
>                             "1" (&__FDS_BITS (fdsp)[0])      
\
>                           : "memory");                           
\
>   } while (0)
That said, this is an odd way to implement FD_ZERO.  The crazy asm is equivalent
to a simple memset...

Ciao,

Duncan.

PS: The underlying problem here is probably that __d0 and __d1 are declared as
int, which is only 32 bits in size, while the asm is expecting 64 bits.

Thanks Duncan, 

It seems the bug has been reopened. After reading the comments related to the
bug report, it was not clear if this is fixed in llvm-gcc, or just in clang.

Thanks, 
Cristi

On Feb 16, 2010, at 3:44 PM, Duncan Sands wrote:
> Hi Cristian, this is (part of) bug 3373, see
>  http://llvm.org/bugs/show_bug.cgi?id=3373
> 
>> 	FD_ZERO(&rfds);   //this is the error line
> 
> ...
> 
>> # define __FD_ZERO(fdsp) \
>>  do {                                                                  
\
>>    int __d0, __d1;                                                     
\
>>    __asm__ __volatile__ ("cld; rep; " __FD_ZERO_STOS         
\
>>                          : "=c" (__d0), "=D" (__d1)
\
>>                          : "a" (0), "0" (sizeof
(fd_set)                     \
>>                                          / sizeof (__fd_mask)),        
\
>>                            "1" (&__FDS_BITS (fdsp)[0])   
\
>>                          : "memory");                        
\
>>  } while (0)
> 
> That said, this is an odd way to implement FD_ZERO.  The crazy asm is
equivalent
> to a simple memset...
> 
> Ciao,
> 
> Duncan.
> 
> PS: The underlying problem here is probably that __d0 and __d1 are declared
as
> int, which is only 32 bits in size, while the asm is expecting 64 bits.