I tried to convert and interpret C language code into assembly language with GCC -S option.
What is the difference between push %rbp and push rbp?
What does % mean on register names in assembly language?
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1 Answers
Both statements you gave do the same thing, the main difference is in the syntax.
There are 2 major syntax conventions for X86, the Intel convention and the AT&T convention.
See syntax comparison for details.
[UPD:] Just in case, duplicating the syntax information here:
| AT&T | Intel | |
|---|---|---|
| Parameter order | Source before the destination.movl $5, %eax |
Destination before source.mov eax, 5 |
| Parameter size | Mnemonics are suffixed with a letter indicating the size of the operands: q for qword, l for long (dword), w for word, and b for byte.addl $4, %esp |
Derived from the name of the register that is used (e.g. rax, eax, ax, al imply q, l, w, b, respectively).add esp, 4 |
| Sigils | Immediate values prefixed with a $, registers prefixed with a %. | The assembler automatically detects the type of symbols; i.e., whether they are registers, constants or something else. |
| Effective addresses | General syntax of DISP(BASE,INDEX,SCALE).movl mem_addr(%ebx,%ecx,4), %eax |
Arithmetic expressions in square brackets; additionally, size keywords like byte, word, or dword have to be used if the size cannot be determined from the operands.mov eax, [ebx + ecx*4 + mem_addr] |
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