title: Inline asm in GCC, specifying offset by expression
body: <p>Not exactly sure how to title this, but
  I want to emulate this code:</p>
  
  <pre><code>asm("movl %%fs:0x30, %0" : "=r" (peb) : : );
  </code></pre>
  
  <p>but I want to specify the offset variably in C</p>
  
  <p>trying:</p>
  
  <pre><code>    int mee = 48;
  asm("movl %%fs:%1, %0"
  
       : "=r" (peb)
       : "r" (mee)
       :
       );
  </code></pre>
  
  <p>Error is <code>bad memory operand '%eax'</code></p>