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    <p>The following answer applies to x86 64bit assembler.</p> <p>Short answer: x86 does not have %s as some kind of assembler instruction, that is pure c and even java nowadays aswell. </p> <p>Long answer:</p> <ul> <li><p>Compile your program with symbols (non stripped): <code>gcc -g yourprogram.c</code></p></li> <li><p>Dump the assembly with intermixed c-code: <code>objdump -S yourProgram.o</code></p></li> </ul> <p>The following text shows how <code>strcpy</code> and <code>printf</code> is shown in assembly. I have also added how you should read the assembly:</p> <pre><code>strcpy(buf, argv[1]); 4005eb: 48 8b 85 60 ff ff ff mov -0xa0(%rbp),%rax Move argv[0] to %rax register 4005f2: 48 83 c0 08 add $0x8,%rax Add 8 to %rax which means we now store argv[1] 4005f6: 48 8b 10 mov (%rax),%rdx Copy argv[1] to the destination register %rdx 4005f9: 48 8d 85 70 ff ff ff lea -0x90(%rbp),%rax Move buf to %rax 400600: 48 89 d6 mov %rdx,%rsi Move argv[1] to %esi which is the source register implicitly used by string funcs 400603: 48 89 c7 mov %rax,%rdi Move buf to destination register 400606: e8 85 fe ff ff callq 400490 &lt;strcpy@plt&gt; Call strcpy which uses %rsi and %rdi Now we have argv[1] in buf, right!? printf("%s\n", buf); 40060b: 48 8d 85 70 ff ff ff lea -0x90(%rbp),%rax The first line loads what you have at the base pointer -0x90 to the %rax register which means that it loads the address of buf into rax as buf is on the stack. 400612: 48 89 c7 mov %rax,%rdi Just mov it to the %rdi register. 400615: e8 86 fe ff ff callq 4004a0 &lt;puts@plt&gt; Call the puts function with buf </code></pre>
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