Assembly syntax

[fctorial]

What is the assembler and assembly dialect used in fuchsia project? The assembly files use constructs like `DATA`, `END_DATA`, `FUNCTION`, `END_FUNCTION` which aren't documented in gnu assembler reference. The argument order of instructions is also different.

[Sam Hansen]

Those are simply macros defined in zircon/kernel/include/asm.h

Unless you configure otherwise (by way of --variant), clang is used as
the compiler (and associated toolchain).

See: docs/development/build/toolchain.md for more info.

Also, note that the tree contains assembly listings for different
architectures (namely, aarch64 and x86), which source were you looking
at?

On Tue, Dec 22, 2020 at 6:49 AM fctorial <fcto...@gmail.com> wrote:
>
> What is the assembler and assembly dialect used in fuchsia project? The assembly files use constructs like `DATA`, `END_DATA`, `FUNCTION`, `END_FUNCTION` which aren't documented in gnu assembler reference. The argument order of instructions is also different.
>

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[fctorial]

I was reading 'zircon/kernel/arch/x86/asm.S'. The argument order is same as gas.

[Roland McGrath]

Fuchsia's code can be built by the Clang compiler using --target=*-fuchsia.  On x86-64 (--target=x86_64-fuchsia), this uses so-called AT&T assembly syntax, the same syntax most commonly used on Linux and other ELF-based systems (I believe this syntax is also used on macOS/x86).  We do not use so-called Intel assembly syntax, which is what is used on Windows and what appears in Intel's processor manuals.  On AArch64, there is a single common assembly syntax specified by ARM and that's what Clang supports for --target=aarch64-fuchsia.

Note that .S files are assembler-with-cpp, so they can use C-style macros and `#include` and such.  In the Fuchsia code base all assembly files we write are .S files that can use the C preprocessor.  We also use GNU-style assembler macros (defined with `.macro`) in some places, and have some header files defining some of those as well as header files that define C-style macros used in assembly code.