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1.5: Assembly code

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  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    Similar to the -c flag, the -S flag tells gcc to compile the program and generate assembly code, which is basically a human-readable form of machine code.

    $ gcc hello.c -S

    The result is a file named hello.s, which might look something like this:

            .file        "hello.c"
            .section     .rodata
            .string      "Hello World"
            .globl       main
            .type        main, @function
            pushq %rbp
            .cfi_def_cfa_offset 16
            .cfi_offset 6, -16
            movq %rsp, %rbp
            .cfi_def_cfa_register 6
            movl $.LC0, %edi
            call puts
            movl $0, %eax
            popq %rbp
            .cfi_def_cfa 7, 8
            .size        main, .-main
            .ident       "GCC: (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3"
            .section     .note.GNU-stack,"",@progbits

    gcc is usually configured to generate code for the machine you are running on, so for me it generates x86 assembly language, which runs on a wide variety of processors from Intel, AMD, and others. If you are running on a different architecture, you might see different code.

    This page titled 1.5: Assembly code is shared under a CC BY-NC license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .

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