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#![no_std]
//! This crate provides the [`asm_block!`] macro for allowing composition
//! through Rust macro when writing inline assembly.
//!
//! [`asm!`] in Rust accepts a template string as input. While it automatically
//! add `\n` between comma-separated strings, it relies solely on the assembler
//! macros to build composable assembly. While it is fine in most cases, it
//! becomes a problem when we want to use the same macro across functions.
//!
//! # Motivation
//! Consider the following code using `x86_64` assembly:
//! ```no_run
//! # use std::arch::asm;
//! # #[cfg(target_arch = "x86_64")]
//! unsafe fn f() -> u64 {
//! let mut x = 20;
//! asm!(
//! ".macro mad x, y",
//! " mul x, y",
//! " lea x, [x + y]",
//! ".endm",
//! "mad {x}, 5",
//!
//! x = inout(reg) x
//! );
//! x
//! }
//! # unsafe { println!("{}", f()) };
//! ```
//! If we want to reuse `mad` in another function, we must copy the verbatim
//! of the macro and change its name. Otherwise we will encounter compilation
//! error due to name collision.
//! ```compile_fail
//! # use std::arch::asm;
//! # #[cfg(target_arch = "x86_64")]
//! unsafe fn f() -> u64 {
//! let mut x = 20;
//! asm!(
//! ".macro mad x, y",
//! " mul x, y",
//! " lea x, [x + y]",
//! ".endm",
//! "mad {x}, 5",
//!
//! x = inout(reg) x
//! );
//! x
//! }
//!
//! # #[cfg(target_arch = "x86_64")]
//! unsafe fn g() -> u64 {
//! let mut x = 10;
//! asm!(
//! // Only compiles if we remove this macro definition
//! // or rename it to another name
//! ".macro mad x, y",
//! " mul x, y",
//! " lea x, [x + y]",
//! ".endm",
//! "mad {x}, 8",
//!
//! x = inout(reg) x
//! );
//! x
//! }
//! # unsafe { println!("{} {}", f(), g()) };
//! # // Make it fails to compile on other target
//! # #[cfg(not(target_arch = "x86_64"))]
//! # this_should_fail_to_compile
//! ```
//! The above code fails with
//! ```text
//! error: macro 'mad' is already defined
//! ```
//! If we omit the definition of `mad` in `g()`, it will compile, but only
//! when `g()` is emitted after `f()`. It is unclear which function should house
//! the definition, so the only sane option is to house it in a `global_asm!`
//! code. But again, it is hard to guarantee that the definition is emitted
//! before the actual use.
//!
//! It is natural to resort to Rust macro in this case, but due to the fact that
//! [`asm!`] accepts a template string, substituting metavariables becomes
//! tedious.
//! ```no_run
//! # use std::arch::asm;
//! macro_rules! mad {
//! ($x: ident, $y: literal) => {
//! concat!(
//! "mul {", stringify!($x), "}, ", stringify!($y), "\n",
//! "lea {", stringify!($x), "}, [{", stringify!($x), "}+", stringify!($y), "]"
//! )
//! };
//! }
//! # #[cfg(target_arch = "x86_64")]
//! unsafe fn f() -> u64 {
//! let mut x = 20;
//! asm!(
//! mad!(x, 5),
//!
//! x = inout(reg) x
//! );
//! x
//! }
//! # unsafe { println!("{}", f()) };
//! ```
//! This approach has some multiple drawbacks:
//! - The definition is very noisy, making it hard to read and comprehend. It is
//! much worse if the definition becomes longer, and much much worse if
//! `rustfmt` attempts to format it.
//! - It is easy to forget `,` and `\n` when the definition becomes longer.
//! - `mad!` can only accept a named register as the first argument and a
//! literal as the second argument. We cannot call `mad!(x, rbx)` or
//! `mad!([rax], rbp)`, which we would have been able to if we were using the
//! assembler macro. Trying to fix this by changing `ident` and `literal` to
//! `tt` is also problematic, since `stringify!({x})` becomes `"{ x }"`, and
//! it is an invalid placeholder.
//!
//! This crate tries to address this by providing a macro that makes it easier
//! to compose assembly code.
//!
//! # Example
//! Instead of the code above, using [`asm_block!`], we are able to write the
//! following:
//! ```no_run
//! # use std::arch::asm;
//! use asm_block::asm_block;
//! macro_rules! mad {
//! ($x: tt, $y: tt) => {
//! asm_block! {
//! mul $x, $y;
//! lea $x, [$x + $y];
//! }
//! };
//! }
//! # #[cfg(target_arch = "x86_64")]
//! #[rustfmt::skip::macros(mad)]
//! unsafe fn f() -> u64 {
//! let mut x = 20;
//! asm!(
//! mad!({x}, 5),
//!
//! x = inout(reg) x
//! );
//! x
//! }
//! # unsafe { println!("{}", f()) };
//! ```
//! Now we are able to make calls like `mad!({x}, rbx)`, `mad!([rax], rbp)`, and
//! `mad!({x:e}, [rsp - 4])`.
//!
//! # Limitations
//! - Due to the tokenization rule of Rust macro, strings enclosed by `'` are
//! not supported.
//! - [`asm_block!`] mostly consumes tokens one by one, so it is possible to run
//! out of recursion limit if the assembly code is long. User needs
//! `#![recursion_limit = "<a_larger_value>"]` when encountering the error.
//! - `rustfmt` will format `mad!({x}, 5)` into `mad!({ x }, 5)`. While this
//! won't make any difference in the emitted assembly code, it is confusing to
//! read when the user is expecting a format placeholder. User can use
//! `#[rustfmt::skip::macros(mad)]` to prevent `rustfmt` from formatting the
//! interior of `mad!` calls.
//! - Some assemblers use `;` as the comment starter, but we are using it as
//! instruction delimeter, so assembly comments may not work properly. Users
//! are strongly suggested to stick to Rust comments.
//! - `tt` cannot capture multiple tokens, so to make `mad!(dword ptr [rax],
//! ebp)` possible, calling convention of `mad!` needs to be changed. For
//! example
//! ```no_run
//! use asm_block::asm_block;
//! macro_rules! mad {
//! ([{ $($x: tt)+ }], $y: tt) => {
//! asm_block! {
//! mul $($x)+, $y;
//! lea $($x)+, [$($x)+ + $y];
//! }
//! };
//! ($x: tt, $y: tt) => { mad!([{ $x }], $y) };
//! }
//! # #[cfg(target_arch = "x86_64")]
//! # unsafe {
//! # use std::arch::asm;
//! # asm!(
//! # mad!([{ dword ptr [{x}] }], ebp),
//! #
//! # x = out(reg) _
//! # );
//! # }
//! ```
//! But `mad!` must be called with `mad!([{ dword ptr [rax] }], ebp)` instead.
//! - Currently we don't have an escape hatch to manually inject assembly if the
//! macro is not able to emit the correct assembly code.
//!
//! # License
//! Dual licensed under the Apache 2.0 license and the MIT license.
//!
//! [`asm_block!`]: macro.asm_block.html
//! [`asm!`]: https://doc.rust-lang.org/stable/core/arch/macro.asm.html
/// Translate tokens to a string containing assembly.
///
/// This evaluates to a `&'static str`. Most input should be transformed as-is in to a
/// string, but there will likely be extra whitespaces or shrunken whitespaces.
///
/// # How it Works
/// This macro follows very simple rules and mostly relies on the whitespace leniency
/// of the underlying assembler.
///
/// Transformation rules:
/// - Convert `;` to `\n`.
/// - No space before and after `@`, `:`.
/// - Must have a space after `.<ident>`.
/// - Not violating the previous rule, no space before `.`.
/// - Concatenate everything inside a pair of `{` and `}` without any space.
/// - Transcribe all the other tokens as-is (by `stringify!`), and add a space afterwards.
///
/// This should work for most assembly code.
///
/// # Example
/// ```no_run
/// # use std::arch::asm;
/// use asm_block::asm_block;
/// macro_rules! f {
/// ($a: tt, $b: tt, $c: tt, $d: tt, $k: tt, $s: literal, $t: literal, $tmp: tt) => {
/// asm_block! {
/// mov $tmp, $c;
/// add $a, $k;
/// xor $tmp, $d;
/// and $tmp, $b;
/// xor $tmp, $d;
/// lea $a, [$a + $tmp + $t];
/// rol $a, $s;
/// add $a, $b;
/// }
/// };
/// }
///
/// # #[cfg(target_arch = "x86_64")]
/// # unsafe {
/// asm!(
/// f!(eax, ebx, ecx, edx, [ebp + 4], 7, 0xd76aa478, esi),
/// f!({a}, {b}, {c}, {d}, {x0}, 7, 0xd76aa478, {t}),
/// f!({a:e}, {b:e}, {c:e}, {d:e}, [{x} + 4], 7, 0xd76aa478, {t:e}),
///
/// a = out(reg) _,
/// b = out(reg) _,
/// c = out(reg) _,
/// d = out(reg) _,
/// x0 = out(reg) _,
/// x = out(reg) _,
/// t = out(reg) _,
/// );
/// # }
/// ```
#[allow(clippy::deprecated_cfg_attr)]
#[cfg_attr(rustfmt, rustfmt::skip)]
#[macro_export]
macro_rules! asm_block {
// base case
() => { "" };
// convert `;` to newline
(; $($token: tt)*) => {
concat!("\n", $crate::asm_block!($($token)*))
};
// no space between an `ident` and a `:`
($first: ident : $($token: tt)*) => {
concat!(stringify!($first), $crate::asm_block!(: $($token)*))
};
// no space between an `ident` and a `@`
($first: ident @ $($token: tt)*) => {
concat!(stringify!($first), $crate::asm_block!(@ $($token)*))
};
// no space between an `ident` and a `.`
($first: ident . $($token: tt)*) => {
concat!(stringify!($first), $crate::asm_block!(. $($token)*))
};
// no space after `:`, `@`
(: $($token: tt)*) => {
concat!(":", $crate::asm_block!($($token)*))
};
(@ $($token: tt)*) => {
concat!("@", $crate::asm_block!($($token)*))
};
// must have a space after `.<tt>`
(. $first: tt $($token: tt)*) => {
concat!(".", stringify!($first), " ", $crate::asm_block!($($token)*))
};
// stringify inside {} and ''
({$($token_inside: tt)*} $($token: tt)*) => {
concat!("{", $(stringify!($token_inside),)* "}", $crate::asm_block!($($token)*))
};
// expand `[]` and `()`
([$($token_inside: tt)*] $($token: tt)*) => {
concat!("[", $crate::asm_block!($($token_inside)*), "] ", $crate::asm_block!($($token)*))
};
(($($token_inside: tt)*) $($token: tt)*) => {
concat!("(", $crate::asm_block!($($token_inside)*), ") ", $crate::asm_block!($($token)*))
};
// For all other type of tokens, add a space after
($first: tt $($token: tt)*) => {
concat!(stringify!($first), " ", $crate::asm_block!($($token)*))
};
}
#[cfg(test)]
#[rustfmt::skip::macros(asm_block)]
mod tests {
#[test]
fn test_single_item() {
assert_eq!(asm_block!(), "");
assert_eq!(asm_block!(eax), "eax ");
assert_eq!(asm_block!(mov), "mov ");
assert_eq!(asm_block!(_WriteConsoleA@20), "_WriteConsoleA@20 ");
assert_eq!(asm_block!(@20), "@20 ");
assert_eq!(asm_block!(@a), "@a ");
assert_eq!(asm_block!(%0), "% 0 ");
assert_eq!(asm_block!(%a), "% a ");
assert_eq!(asm_block!(%a@0), "% a@0 ");
assert_eq!(asm_block!(%{a}), "% {a}");
assert_eq!(asm_block!(#0), "# 0 ");
assert_eq!(asm_block!(#a), "# a ");
assert_eq!(asm_block!(#a_0), "# a_0 ");
assert_eq!(asm_block!(.0), ".0 ");
assert_eq!(asm_block!(.a), ".a ");
assert_eq!(asm_block!(.a_0), ".a_0 ");
assert_eq!(asm_block!("$a"), r#""$a" "#);
assert_eq!(asm_block!(${a}), "$ {a}");
assert_eq!(asm_block!(${a:e}), "$ {a:e}");
assert_eq!(asm_block!(v19.4s), "v19.4s ");
assert_eq!(asm_block!(v1.4s), "v1.4s ");
assert_eq!(asm_block!({x:v}.4s), "{x:v}.4s ");
assert_eq!(asm_block!(a), "a ");
assert_eq!(asm_block!(A), "A ");
assert_eq!(asm_block!(0), "0 ");
assert_eq!(asm_block!(0x1234), "0x1234 ");
assert_eq!(asm_block!(-0x1234), "- 0x1234 ");
assert_eq!(
asm_block!(gs:[eax + 4*{b:e} - 0x30]),
"gs:[eax + 4 * {b:e}- 0x30 ] "
);
assert_eq!(asm_block!(%gs:4(,%eax,8)), "% gs:4 (, % eax , 8 ) ");
}
#[test]
fn test_single_instruction() {
assert_eq!(asm_block!(mov {x}, [{x}]), "mov {x}, [{x}] ");
assert_eq!(asm_block!(inc), "inc ");
assert_eq!(asm_block!(_start: mov rax, 1), "_start:mov rax , 1 ");
assert_eq!(asm_block!(mov $1, %rax), "mov $ 1 , % rax ");
assert_eq!(asm_block!(.section .text), ".section .text ");
assert_eq!(asm_block!(L001:), "L001:");
assert_eq!(
asm_block!(pushl %fs:table(%ebx, %ecx, 8)),
"pushl % fs:table (% ebx , % ecx , 8 ) "
);
assert_eq!(
asm_block!(message: db "Hello, World", 10),
r#"message:db "Hello, World" , 10 "#
);
assert_eq!(
asm_block!(.ascii "Hello, world\n"),
r#".ascii "Hello, world\n" "#
);
assert_eq!(
asm_block!(call _WriteConsoleA@20),
"call _WriteConsoleA@20 "
);
assert_eq!(asm_block!(str fp, [sp, -4]!), "str fp , [sp , - 4 ] ! ");
assert_eq!(asm_block!(ldr fp, [{x}], 4), "ldr fp , [{x}] , 4 ");
assert_eq!(
asm_block!(add v19.4s, v2.4s, v4.4s),
"add v19.4s , v2.4s , v4.4s "
);
}
#[test]
fn test_block() {
assert_eq!(
asm_block! {
push 0;
push offset written;
push 13;
push offset msg;
push handle;
call _WriteConsoleA@20;
},
"\
push 0
push offset written
push 13
push offset msg
push handle
call _WriteConsoleA@20
"
);
assert_eq!(
asm_block! {
mov {t1:e}, {d:e};
not {t1:e};
add {a:e}, {k:e};
or {t1:e}, {b:e};
xor {t1:e}, {c:e};
lea {a:e}, [{a:e} + {t1:e} + 0xf4d50d87];
rol {a:e}, 7;
add {a:e}, {b:e};
},
"\
mov {t1:e}, {d:e}
not {t1:e}
add {a:e}, {k:e}
or {t1:e}, {b:e}
xor {t1:e}, {c:e}
lea {a:e}, [{a:e}+ {t1:e}+ 0xf4d50d87 ]
rol {a:e}, 7
add {a:e}, {b:e}
"
);
}
#[test]
#[rustfmt::skip::macros(f)]
fn test_substitute() {
macro_rules! f {
($a: tt, $b: tt, $c: tt, $d: tt, $k: tt, $s: literal, $t: literal, $tmp: tt) => {
asm_block! {
mov $tmp, $c;
add $a, $k;
xor $tmp, $d;
and $tmp, $b;
xor $tmp, $d;
lea $a, [$a + $tmp + $t];
rol $a, $s;
add $a, $b;
}
};
}
assert_eq!(
f!({a}, {b}, {c}, {d}, {x0}, 7, 0xd76aa478, {t1}),
"\
mov {t1}, {c}
add {a}, {x0}
xor {t1}, {d}
and {t1}, {b}
xor {t1}, {d}
lea {a}, [{a}+ {t1}+ 0xd76aa478 ]
rol {a}, 7
add {a}, {b}
"
);
assert_eq!(
f!({a:e}, {b:e}, {c:e}, {d:e}, {x0:e}, 7, 0xd76aa478, {t1:e}),
"\
mov {t1:e}, {c:e}
add {a:e}, {x0:e}
xor {t1:e}, {d:e}
and {t1:e}, {b:e}
xor {t1:e}, {d:e}
lea {a:e}, [{a:e}+ {t1:e}+ 0xd76aa478 ]
rol {a:e}, 7
add {a:e}, {b:e}
"
);
assert_eq!(
f!(eax, ebx, ecx, edx, [ebp + 4], 7, 0xd76aa478, esi),
"\
mov esi , ecx
add eax , [ebp + 4 ]
xor esi , edx
and esi , ebx
xor esi , edx
lea eax , [eax + esi + 0xd76aa478 ]
rol eax , 7
add eax , ebx
"
);
}
}