RE: [PATCH] linuxthreads/sysdeps/i386/useldt.h

[Ed Connell]

Ulrich Drepper writes:
> Ed Connell <address@hidden> writes:
> 
> > This patch forces gcc to use an 8-bit register (i.e. %cl) for one
> > byte values and a 32-bit register (i.e. %ecx) for 4 byte values.
> > Otherwise gcc complains that the wrong register type is used in the
> > branch that is not taken.
>
> Simply use values of the right type.  The patch is not necessary.

Say you call THREAD_GETMEM() with the member being of type char.
Clearly we take the 'if' part of the macro but we get a compile 
error in the else part.  Since __value is a char, gcc gives it
an 8-bit register (say %cl).  But movl isn't allowed to have %cl
as a register (32-bit move into an 8-bit register) and gcc fails.
The reverse happens if member is an int.

Please reconsider.

Cheers,
Ed Connell

Here is the THREAD_GETMEM() part of the patch for reference.
#define THREAD_GETMEM(descr, member) \ 
   ({                                                                           
\ 
     __typeof__ (descr->member) __value;                                        
\ 
     if (sizeof (__value) == 1)                                                 
\ 
       __asm__ __volatile__ ("movb %%gs:%P2,%b0"                                
\ 
  -                         : "=q" (__value)                                    
\ 
  +                         : "=q" ((int8_t)(__value))                          
\ 
                            : "0" (0),                                          
\ 
                              "i" (offsetof (struct _pthread_descr_struct,      
\ 
                                             member)));                         
\ 
     else                                                                       
\ 
       {                                                                        
\ 
         if (sizeof (__value) != 4)                                             
\ 
          /* There should not be any value with a size other than 1 or 4.  */   
\ 
          abort ();                                                             
\ 
                                                                                
\ 
         __asm__ __volatile__ ("movl %%gs:%P1,%0"                               
\ 
  -                           : "=r" (__value)                                  
\ 
  +                           : "=r" ((int32_t)(__value))                       
\ 
                              : "i" (offsetof (struct _pthread_descr_struct,    
\ 
                                               member)));                       
\ 
       }                                                                        
\ 
     __value;                                                                   
\ 
   })