[MIPS] Fix constraint modifier for syscall clone

lss/linux_syscall_support.h

 /* Copyright (c) 2005-2011, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 2424 matching lines @@
                           type5 arg5,type6 arg6) {                            \
         LSS_REG(4, arg1); LSS_REG(5, arg2); LSS_REG(6, arg3);                 \
         LSS_REG(7, arg4); LSS_REG(8, arg5); LSS_REG(9, arg6);                 \
         LSS_BODY(type, name, "+r", "r"(__r4), "r"(__r5), "r"(__r6),           \
                  "r"(__r8), "r"(__r9));                                       \
       }
     #endif
     LSS_INLINE int LSS_NAME(clone)(int (*fn)(void *), void *child_stack,
                                    int flags, void *arg, int *parent_tidptr,
                                    void *newtls, int *child_tidptr) {
       register unsigned long __v0 __asm__("$2");

[Mark Seaborn, 2013/04/09 00:29:55]

Background question (since I'm not very familiar with the MIPS code here):  Why
does this code use reg numbers ($2) rather than names ($v0)?

[petarj, 2013/04/09 12:17:40]

Older binutils could not recognize symbolic register names, so I assume
whoever wrote the original code had an older version of binutils or wanted
to support older versions.

       register unsigned long __r7 __asm__("$7") = (unsigned long)newtls;
       {

[Mark Seaborn, 2013/04/09 00:29:55]

Background question: Why is there a block here?

[petarj, 2013/04/09 12:17:40]

I do not know. It does not seem like it is needed.

         register int   __flags __asm__("$4") = flags;
         register void *__stack __asm__("$5") = child_stack;
         register void *__ptid  __asm__("$6") = parent_tidptr;
         register int  *__ctid  __asm__("$8") = child_tidptr;
         __asm__ __volatile__(
           #if _MIPS_SIM == _MIPS_SIM_ABI32 && _MIPS_SZPTR == 32
                              "subu  $29,24\n"
           #elif _MIPS_SIM == _MIPS_SIM_NABI32
                              "sub   $29,16\n"
           #else
@@ skipping 60 matching lines @@
                             "syscall\n"
 
                            "1:\n"
           #if _MIPS_SIM == _MIPS_SIM_ABI32 && _MIPS_SZPTR == 32
                              "addu  $29, 24\n"
           #elif _MIPS_SIM == _MIPS_SIM_NABI32
                              "add   $29, 16\n"
           #else
                              "daddu $29,16\n"
           #endif
-                             : "=&r" (__v0), "+r" (__r7)
+                             : "+r" (__v0), "+r" (__r7)
                              : "i"(-EINVAL), "i"(__NR_clone), "i"(__NR_exit),
                                "r"(fn), "r"(__stack), "r"(__flags), "r"(arg),
                                "r"(__ptid), "r"(__r7), "r"(__ctid)
                              : "$9", "$10", "$11", "$12", "$13", "$14", "$15",
                                "$24", "$25", "memory");
       }
       LSS_RETURN(int, __v0, __r7);
     }
   #elif defined (__PPC__)
     #undef  LSS_LOADARGS_0
@@ skipping 1124 matching lines @@
 # pragma pop_macro("fstat64")
 # pragma pop_macro("lstat64")
 #endif
 
 #if defined(__cplusplus) && !defined(SYS_CPLUSPLUS)
 }
 #endif
 
 #endif
 #endif