asm inline

Ian Lance Taylor iant@google.com
Tue Jul 24 22:07:00 GMT 2012


On Tue, Jul 24, 2012 at 2:31 PM, Sergey Ivanov <icegood1980@gmail.com> wrote:
> Have code:
>   #define MoveIntArrayToRight(IntCnt, LastSrcPos) \
>     __asm__ __volatile__                          \
>     (                                             \
>      "std\n\t"                                    \
>      "movl 4(%%esi), %%edi\n\t"                   \
>      "rep\n\tmovsl\n\t"                           \
>      "cld\n\t"                                    \
>      :                                            \
>      :"S" (LastSrcPos), "c" (IntCnt)              \
>      : "%ecx", "%esi", "%edi" , "cc", "memory"    \
>     )
>
> why compiler says
> "error: can’t find a register in class ‘CREG’ while reloading ‘asm’"

Because you said that IntCnt has a constaint "c", which means it must
be in %ecx, and you've also said that the asm clobbers %ecx, meaning
that no values can be placed in it.  The asm is unsatisfiable and the
compiler simply crashes.

Ian



More information about the Gcc-help mailing list