Set register using a variable inline assembly

Question

My requirement is to set EDI register using a variable with inline assembly. I wrote the following snippet but it fails to compile.

uint32_t value = 0;
__asm__ __volatile__("mov %1,%%edi \n\t"
                      : "=D"
                      : "ir"  (value)
                      :
                      );

Errors I get are

cyg_functions.cpp(544): error: expected a "(" : "ir" (value) ^

cyg_functions.cpp(544): internal error: null pointer : "ir" (value)

Edit

I guess I wasn't clear on the problem specification. Let's say my requirement is as follows.

• There are two int variables val and result.
• I need to
  1. Set the value of variable val to %%edi clobbering whatever in there already
  2. Multiply %%edi value by 2
  3. Set %%edi value back to result variable

How can this be stated with inline assembly? Though this is not exactly my requirement answer to this (specifically the 1st step) would solve my problem. I need the intermediate to be specifically in EDI register.

Answer 1

I have read your comments, and the requirements here still makes no sense to me. However, making sense is not a requirement. Such being the case:

int main(int argc, char *argv[])
{
   int res;
   int value = argc;

   asm ("shl $1, %[res]" /* Take the value in res (aka EDI) and shift
                            it left by 1. */
      : [res] "=D" (res) /* On exit from the asm, the register EDI 
                            will contain the value for "res".  The
                            existing value of res will be overwritten. */
      : "0" (value));    /* Take the contents of "value" and put it
                            in the same place as parameter #0. */

   return res;
}

This may be easier to understand if you read it from the bottom up.