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    <ol> <li>Your machine is <em>64</em> bit, not 63 bit =). You were able to read the the 32-bit registers because you are compiling and running your program as a 32-bit executable[1].</li> <li>You are unable to read the 64-bit registers because you are compiling and running your program as a 32-bit executable. Yes, you have a 64-bit processor, but it can still run 32-bit executables (if your OS supports it, which yours clearly does), and evidently your compiler tool chain builds 32-bit by default. If you are using <code>gcc</code>, try using the <code>-m64</code> flag, or read the compiler documentation for more information.</li> <li>Unlike <code>rip</code>, the <code>eip</code> register cannot be directly accessed. You can get the value of <code>eip</code> in the manner described by <strong>Jim</strong> in his answer.</li> </ol> <p>[1] you would be able to read the 32-bit registers from a 64-bit executable anyway; the 32-bit registers are still available in 64-bit mode, just like you can access the 16-bit registers in 32-bit mode.</p> <hr> <p>There are a few problems still in your example:</p> <p>First, although <code>rip</code> is accessible in 64-bit mode, it's accessible as an addressing mode; it's not a normal register. If you want to load its value, you need to use <code>LEA</code>, not <code>MOV</code>.</p> <p>Second, because <code>rip</code> is a 64-bit register, you need to use the <code>q</code> suffix on your instructions instead of <code>l</code>. Here's a sample program with these two issues addressed:</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;inttypes.h&gt; int main(int argc, char *argv[]) { uint64_t ip; asm("leaq (%%rip), %0;": "=r"(ip)); printf("rip is 0x%016" PRIx64 "\n", ip); return 0; } </code></pre> <p>which seems to work just fine on my machine.</p>
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    1. POHow do i write Simple inline asm instruction from C on Linux 64 bit?
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    1. USStephen Canon
    1. USStephen Canon
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    1. POHow do i write Simple inline asm instruction from C on Linux 64 bit?
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    1. COyes.it is 64 bit, not 63 bit..
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      1. USSandeep P
    2. COasm("movl (%%rip), %0;" : "=r"(val) ) this statement assigns some value to my variable, but asm("movl %%rip, %0;" : "=r"(val) ) don't and gives compilation Error: suffix or operands invalid for `mov'. again the value which i get from 1st statement does not match with the nm result of my library. i assume that the library has information about the IP address and respective symbol for the functions. is it the correct behavior? the results are same even when i use "-m64" flag. my machine by default has 64 bit settings.
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    3. COi think one more syntax is correct for only reading registers. that is **register int iRIP asm("rip");**; but this too gives compilation error like "error: invalid register name for ΓÇÿiRIPΓÇÖ". it does not give compilation errors for other 64 bit registers. i made it sure that i compiled with -m64 flag of gcc. it looks that rip register cannot be accessed.
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