What assembly language does C code compile into in Visual Studio?

Question

When I debug a C project, I can see all the assembly codes it compiles into. I want to know what assembly language that it. Is it NASM or MASM or something else? And if I use inline assembly, will I be able to use some other assembly language?

Answer 1

The code it compiles to is not assembly, but straight machine code, at least after link-time optimizations. What you see while debugging is on-the-fly disassembly of the machine code that is currently executing. As such, it has no additional structure, such as labels, macros, etc. such that you would expect to find in high-level assemblers, because this extra information is lost (or, more accurately, never present), when producing machine code.

If you meant the syntax, Visual Studio shows the assembly directives in Intel syntax , which is different from AT&T syntax, which is a default with GCC and GNU assembler.

In fact, it may also be gibberish. If you jmp out of alignment (x86 instructions are variable-length), or to a region that does not contain executable code, but rather data, the disassembler will try to make sense of the data, producing random assembly directives that don't mean anything.

This is actually quite common; see for example this image:

add byte ptr [rax], al is the attempted disassembly of bytes 00 00 , which obviously does not represent actual executable code.

Answer 2

MSVC can compile binaries for x86, x86_64, ARM and Itanium. So it depends on your target and project settings

Answer 3

For X86 or X86-X64, Visual Studio includes ML.EXE (MASM 6.00 and later versions were renamed to ML.EXE) for 32 bit code and ML64.EXE for 64 bit code. On a VS project, you can right click on a file name, then properties, ... output files, ... assembly listing ... . The command line option for assembly listing is /Fa. Although called assembly only listing, it produces assembly code.