separate out display code further, reword comments on InstructionTextSink to be ... stern

1 files changed, 1020 insertions, 0 deletions

diff --git a/src/display.rs b/src/display.rs
new file mode 100644
index 0000000..e495aee
--- /dev/null
+++ b/src/display.rs
@@ -0,0 +1,1020 @@
+use core::fmt;
+
+use crate::safer_unchecked::unreachable_kinda_unchecked;
+
+extern crate alloc;
+
+// TODO: find a better place to put this....
+fn c_to_hex(c: u8) -> u8 {
+    /*
+    static CHARSET: &'static [u8; 16] = b"0123456789abcdef";
+    CHARSET[c as usize]
+    */
+    // the conditional branch below is faster than a lookup, yes
+    if c < 10 {
+        b'0' + c
+    } else {
+        b'a' + c - 10
+    }
+}
+
+pub enum TokenType {
+    Mnemonic,
+    Operand,
+    Immediate,
+    Register,
+    Offset,
+}
+
+/// `DisplaySink` allows client code to collect output and minimal markup. this is currently used
+/// in formatting instructions for two reasons:
+/// * `DisplaySink` implementations have the opportunity to collect starts and ends of tokens at
+///   the same time as collecting output itself.
+/// * `DisplaySink` implementations provides specialized functions for writing strings in
+///   circumstances where a simple "use `core::fmt`" might incur unwanted overhead.
+///
+/// spans are reported through `span_start` and `span_exit` to avoid constraining implementations
+/// into tracking current output offset (which may not be knowable) or span size (which may be
+/// knowable, but incur additional overhead to compute or track).
+///
+/// spans are entered and exited in a FILO manner: a function writing to some `DisplaySink` must
+/// exit spans in reverse order to when they are entered. a function sequence like
+/// `sink.span_start(Operand); sink.span_start(Immediate); sink.span_exit(Operand)` is in error.
+///
+/// the `write_*` helpers on `DisplaySink` may be able to take advantage of contraints described in
+/// documentation here to better support writing some kinds of inputs than a fully-general solution
+/// (such as `core::fmt`) might be able to yield.
+///
+/// currently there are two motivating factors for `write_*` helpers:
+///
+/// instruction formatting often involves writing small but variable-size strings, such as register
+/// names, which is something of a pathological case for string appending as Rust currently exists:
+/// this often becomes `memcpy` and specifically a call to the platform's `memcpy` (rather than an
+/// inlined `rep movsb`) just to move 3-5 bytes. one relevant Rust issue for reference:
+/// https://github.com/rust-lang/rust/issues/92993#issuecomment-2028915232
+///
+/// there are similar papercuts around formatting integers as base-16 numbers, such as
+/// https://github.com/rust-lang/rust/pull/122770 . in isolation and in most applications these are
+/// not a significant source of overhead. but for programs bounded on decoding and printing
+/// instructions, these can add up to significant overhead - on the order of 10-20% of total
+/// runtime.
+///
+/// `DisplaySink`
+pub trait DisplaySink: fmt::Write {
+    #[inline(always)]
+    fn write_fixed_size(&mut self, s: &str) -> Result<(), core::fmt::Error> {
+        self.write_str(s)
+    }
+
+    /// write a string to this sink that is less than 32 bytes. this is provided for optimization
+    /// opportunities when writing a variable-length string with known max size.
+    ///
+    /// SAFETY: the provided `s` must be less than 32 bytes. if the provided string is longer than
+    /// 31 bytes, implementations may only copy part of a multi-byte codepoint while writing to a
+    /// utf-8 string. this may corrupt Rust strings.
+    unsafe fn write_lt_32(&mut self, s: &str) -> Result<(), core::fmt::Error> {
+        self.write_str(s)
+    }
+    /// write a string to this sink that is less than 16 bytes. this is provided for optimization
+    /// opportunities when writing a variable-length string with known max size.
+    ///
+    /// SAFETY: the provided `s` must be less than 16 bytes. if the provided string is longer than
+    /// 15 bytes, implementations may only copy part of a multi-byte codepoint while writing to a
+    /// utf-8 string. this may corrupt Rust strings.
+    unsafe fn write_lt_16(&mut self, s: &str) -> Result<(), core::fmt::Error> {
+        self.write_str(s)
+    }
+    /// write a string to this sink that is less than 8 bytes. this is provided for optimization
+    /// opportunities when writing a variable-length string with known max size.
+    ///
+    /// SAFETY: the provided `s` must be less than 8 bytes. if the provided string is longer than
+    /// 7 bytes, implementations may only copy part of a multi-byte codepoint while writing to a
+    /// utf-8 string. this may corrupt Rust strings.
+    unsafe fn write_lt_8(&mut self, s: &str) -> Result<(), core::fmt::Error> {
+        self.write_str(s)
+    }
+
+    /// write a u8 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    fn write_u8(&mut self, v: u8) -> Result<(), core::fmt::Error> {
+        write!(self, "{:x}", v)
+    }
+    /// write a u16 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    fn write_u16(&mut self, v: u16) -> Result<(), core::fmt::Error> {
+        write!(self, "{:x}", v)
+    }
+    /// write a u32 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    fn write_u32(&mut self, v: u32) -> Result<(), core::fmt::Error> {
+        write!(self, "{:x}", v)
+    }
+    /// write a u64 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    fn write_u64(&mut self, v: u64) -> Result<(), core::fmt::Error> {
+        write!(self, "{:x}", v)
+    }
+    /// enter a region inside which output corresponds to a `ty`.
+    ///
+    /// the default implementation of these functions is as a no-op. this way, providing span
+    /// information to a `DisplaySink` that does not want it is eliminated at compile time.
+    ///
+    /// spans are entered and ended in a FILO manner: a function writing to some `DisplaySink` must
+    /// end spans in reverse order to when they are entered. a function sequence like
+    /// `sink.span_start(Operand); sink.span_start(Immediate); sink.span_end(Operand)` is in error.
+    ///
+    /// a simple use of `span_start`/`span_end` might look something like:
+    /// ```compile_fail
+    /// sink.span_start(Operand)
+    /// sink.write_char('[')
+    /// sink.span_start(Register)
+    /// sink.write_fixed_size("rbp")
+    /// sink.span_end(Register)
+    /// sink.write_char(']')
+    /// sink.span_end(Operand)
+    /// ```
+    /// which writes the text `[rbp]`, with span indicators where the operand (`[ ... ]`) begins,
+    /// as well as the start and end of a register name.
+    fn span_start(&mut self, _ty: TokenType) { }
+    /// end a region where a `ty` was written. see docs on [`DisplaySink::span_start`] for more.
+    fn span_end(&mut self, _ty: TokenType) { }
+}
+
+pub struct NoColorsSink<'a, T: fmt::Write> {
+    pub out: &'a mut T,
+}
+
+impl<'a, T: fmt::Write> DisplaySink for NoColorsSink<'a, T> {
+    fn span_start(&mut self, _ty: TokenType) { }
+    fn span_end(&mut self, _ty: TokenType) { }
+}
+
+impl<'a, T: fmt::Write> fmt::Write for NoColorsSink<'a, T> {
+    fn write_str(&mut self, s: &str) -> Result<(), core::fmt::Error> {
+        self.out.write_str(s)
+    }
+    fn write_char(&mut self, c: char) -> Result<(), core::fmt::Error> {
+        self.out.write_char(c)
+    }
+    fn write_fmt(&mut self, f: fmt::Arguments) -> Result<(), core::fmt::Error> {
+        self.out.write_fmt(f)
+    }
+}
+
+/// this is an implementation detail of yaxpeax-arch and related crates. if you are a user of the
+/// disassemblers, do not use this struct. do not depend on this struct existing. this struct is
+/// not stable. this struct is not safe for general use. if you use this struct you and your
+/// program will be eaten by gremlins.
+///
+/// if you are implementing an instruction formatter for the yaxpeax family of crates: this struct
+/// is guaranteed to contain a string that is long enough to hold a fully-formatted instruction.
+/// because the buffer is guaranteed to be long enough, writes through `InstructionTextSink` are
+/// not bounds-checked, and the buffer is never grown.
+///
+/// this is wildly dangerous in general use. the public constructor of `InstructionTextSink` is
+/// unsafe as a result. as used in `InstructionFormatter`, the buffer is guaranteed to be
+/// `clear()`ed before use, `InstructionFormatter` ensures the buffer is large enough, *and*
+/// `InstructionFormatter` never allows `InstructionTextSink` to exist in a context where it would
+/// be written to without being rewound first.
+///
+/// because this opens a very large hole through which `fmt::Write` can become unsafe, incorrect
+/// uses of this struct will be hard to debug in general. `InstructionFormatter` is probably at the
+/// limit of easily-reasoned-about lifecycle of the buffer, which "only" leaves the problem of
+/// ensuring that instruction formatting impls this buffer is passed to are appropriately sized.
+///
+/// this is intended to be hidden in docs. if you see this in docs, it's a bug.
+#[doc(hidden)]
+pub(crate) struct InstructionTextSink<'buf> {
+    buf: &'buf mut alloc::string::String
+}
+
+impl<'buf> InstructionTextSink<'buf> {
+    pub unsafe fn new(buf: &'buf mut alloc::string::String) -> Self {
+        Self { buf }
+    }
+}
+
+impl<'buf> fmt::Write for InstructionTextSink<'buf> {
+    fn write_str(&mut self, s: &str) -> Result<(), core::fmt::Error> {
+        self.buf.write_str(s)
+    }
+    fn write_char(&mut self, c: char) -> Result<(), core::fmt::Error> {
+        // SAFETY: `buf` is assumed to be long enough to hold all input, `buf` at `underlying.len()`
+        // is valid for writing, but may be uninitialized.
+        //
+        // this function is essentially equivalent to `Vec::push` specialized for the case that
+        // `len < buf.capacity()`:
+        // https://github.com/rust-lang/rust/blob/be9e27e/library/alloc/src/vec/mod.rs#L1993-L2006
+        unsafe {
+            let underlying = self.buf.as_mut_vec();
+            // `InstructionTextSink::write_char` is only used by yaxpeax-x86, and is only used to
+            // write single ASCII characters. this is wrong in the general case, but `write_char`
+            // here is not going to be used in the general case.
+            if cfg!(debug_asertions) {
+                panic!("InstructionTextSink::write_char would truncate output");
+            }
+            let to_push = c as u8;
+            // `ptr::write` here because `underlying.add(underlying.len())` may not point to an
+            // initialized value, which would mean that turning that pointer into a `&mut u8` to
+            // store through would be UB. `ptr::write` avoids taking the mut ref.
+            underlying.as_mut_ptr().offset(underlying.len() as isize).write(to_push);
+            // we have initialized all (one) bytes that `set_len` is increasing the length to
+            // include.
+            underlying.set_len(underlying.len() + 1);
+        }
+        Ok(())
+    }
+}
+
+/// this DisplaySink impl exists to support somewhat more performant buffering of the kinds of
+/// strings `yaxpeax-x86` uses in formatting instructions.
+impl DisplaySink for alloc::string::String {
+    #[inline(always)]
+    fn write_fixed_size(&mut self, s: &str) -> Result<(), core::fmt::Error> {
+        self.reserve(s.len());
+        let buf = unsafe { self.as_mut_vec() };
+        let new_bytes = s.as_bytes();
+
+        if new_bytes.len() == 0 {
+            unsafe { unreachable_kinda_unchecked() }
+        }
+
+        if new_bytes.len() >= 16 {
+            unsafe { unreachable_kinda_unchecked() }
+        }
+
+        unsafe {
+            let dest = buf.as_mut_ptr().offset(buf.len() as isize);
+
+            // this used to be enough to bamboozle llvm away from
+            // https://github.com/rust-lang/rust/issues/92993#issuecomment-2028915232
+            // if `s` is not fixed size. somewhere between Rust 1.68 and Rust 1.74 this stopped
+            // being sufficient, so `write_fixed_size` truly should only be used for fixed size `s`
+            // (otherwise this is a libc memcpy call in disguise). for fixed-size strings this
+            // unrolls into some kind of appropriate series of `mov`.
+            dest.offset(0 as isize).write(new_bytes[0]);
+            for i in 1..new_bytes.len() {
+                dest.offset(i as isize).write(new_bytes[i]);
+            }
+
+            buf.set_len(buf.len() + new_bytes.len());
+        }
+
+        Ok(())
+    }
+    unsafe fn write_lt_32(&mut self, s: &str) -> Result<(), fmt::Error> {
+        self.reserve(s.len());
+
+        // SAFETY: todo
+        let buf = unsafe { self.as_mut_vec() };
+        let new_bytes = s.as_bytes();
+
+        // should get DCE
+        if new_bytes.len() >= 32 {
+            unsafe { core::hint::unreachable_unchecked() }
+        }
+
+        unsafe {
+            let dest = buf.as_mut_ptr().offset(buf.len() as isize);
+            let src = new_bytes.as_ptr();
+
+            let rem = new_bytes.len() as isize;
+
+            // set_len early because there is no way to avoid the following asm!() writing that
+            // same number of bytes into buf
+            buf.set_len(buf.len() + new_bytes.len());
+
+            core::arch::asm!(
+                "6:",
+                "cmp {rem:e}, 16",
+                "jb 7f",
+                "mov {buf:r}, qword ptr [{src} + {rem} - 16]",
+                "mov qword ptr [{dest} + {rem} - 16], {buf:r}",
+                "mov {buf:r}, qword ptr [{src} + {rem} - 8]",
+                "mov qword ptr [{dest} + {rem} - 8], {buf:r}",
+                "sub {rem:e}, 16",
+                "jz 11f",
+                "7:",
+                "cmp {rem:e}, 8",
+                "jb 8f",
+                "mov {buf:r}, qword ptr [{src} + {rem} - 8]",
+                "mov qword ptr [{dest} + {rem} - 8], {buf:r}",
+                "sub {rem:e}, 8",
+                "jz 11f",
+                "8:",
+                "cmp {rem:e}, 4",
+                "jb 9f",
+                "mov {buf:e}, dword ptr [{src} + {rem} - 4]",
+                "mov dword ptr [{dest} + {rem} - 4], {buf:e}",
+                "sub {rem:e}, 4",
+                "jz 11f",
+                "9:",
+                "cmp {rem:e}, 2",
+                "jb 10f",
+                "mov {buf:x}, word ptr [{src} + {rem} - 2]",
+                "mov word ptr [{dest} + {rem} - 2], {buf:x}",
+                "sub {rem:e}, 2",
+                "jz 11f",
+                "10:",
+                "cmp {rem:e}, 1",
+                "jb 11f",
+                "mov {buf:l}, byte ptr [{src} + {rem} - 1]",
+                "mov byte ptr [{dest} + {rem} - 1], {buf:l}",
+                "11:",
+                src = in(reg) src,
+                dest = in(reg) dest,
+                rem = inout(reg) rem => _,
+                buf = out(reg) _,
+                options(nostack),
+            );
+        }
+        /*
+        for i in 0..new_bytes.len() {
+            unsafe {
+                buf.as_mut_ptr().offset(buf.len() as isize).offset(i as isize).write_volatile(new_bytes[i]);
+            }
+        }
+        */
+
+        Ok(())
+    }
+    unsafe fn write_lt_16(&mut self, s: &str) -> Result<(), fmt::Error> {
+        self.reserve(s.len());
+
+        // SAFETY: todo
+        let buf = unsafe { self.as_mut_vec() };
+        let new_bytes = s.as_bytes();
+
+        // should get DCE
+        if new_bytes.len() >= 16 {
+            unsafe { core::hint::unreachable_unchecked() }
+        }
+
+        unsafe {
+            let dest = buf.as_mut_ptr().offset(buf.len() as isize);
+            let src = new_bytes.as_ptr();
+
+            let rem = new_bytes.len() as isize;
+
+            // set_len early because there is no way to avoid the following asm!() writing that
+            // same number of bytes into buf
+            buf.set_len(buf.len() + new_bytes.len());
+
+            core::arch::asm!(
+                "7:",
+                "cmp {rem:e}, 8",
+                "jb 8f",
+                "mov {buf:r}, qword ptr [{src} + {rem} - 8]",
+                "mov qword ptr [{dest} + {rem} - 8], {buf:r}",
+                "sub {rem:e}, 8",
+                "jz 11f",
+                "8:",
+                "cmp {rem:e}, 4",
+                "jb 9f",
+                "mov {buf:e}, dword ptr [{src} + {rem} - 4]",
+                "mov dword ptr [{dest} + {rem} - 4], {buf:e}",
+                "sub {rem:e}, 4",
+                "jz 11f",
+                "9:",
+                "cmp {rem:e}, 2",
+                "jb 10f",
+                "mov {buf:x}, word ptr [{src} + {rem} - 2]",
+                "mov word ptr [{dest} + {rem} - 2], {buf:x}",
+                "sub {rem:e}, 2",
+                "jz 11f",
+                "10:",
+                "cmp {rem:e}, 1",
+                "jb 11f",
+                "mov {buf:l}, byte ptr [{src} + {rem} - 1]",
+                "mov byte ptr [{dest} + {rem} - 1], {buf:l}",
+                "11:",
+                src = in(reg) src,
+                dest = in(reg) dest,
+                rem = inout(reg) rem => _,
+                buf = out(reg) _,
+                options(nostack),
+            );
+        }
+        /*
+        for i in 0..new_bytes.len() {
+            unsafe {
+                buf.as_mut_ptr().offset(buf.len() as isize).offset(i as isize).write_volatile(new_bytes[i]);
+            }
+        }
+        */
+
+        Ok(())
+    }
+    unsafe fn write_lt_8(&mut self, s: &str) -> Result<(), fmt::Error> {
+        self.reserve(s.len());
+
+        // SAFETY: todo
+        let buf = unsafe { self.as_mut_vec() };
+        let new_bytes = s.as_bytes();
+
+        // should get DCE
+        if new_bytes.len() >= 8 {
+            unsafe { core::hint::unreachable_unchecked() }
+        }
+
+        unsafe {
+            let dest = buf.as_mut_ptr().offset(buf.len() as isize);
+            let src = new_bytes.as_ptr();
+
+            let rem = new_bytes.len() as isize;
+
+            // set_len early because there is no way to avoid the following asm!() writing that
+            // same number of bytes into buf
+            buf.set_len(buf.len() + new_bytes.len());
+
+            core::arch::asm!(
+                "8:",
+                "cmp {rem:e}, 4",
+                "jb 9f",
+                "mov {buf:e}, dword ptr [{src} + {rem} - 4]",
+                "mov dword ptr [{dest} + {rem} - 4], {buf:e}",
+                "sub {rem:e}, 4",
+                "jz 11f",
+                "9:",
+                "cmp {rem:e}, 2",
+                "jb 10f",
+                "mov {buf:x}, word ptr [{src} + {rem} - 2]",
+                "mov word ptr [{dest} + {rem} - 2], {buf:x}",
+                "sub {rem:e}, 2",
+                "jz 11f",
+                "10:",
+                "cmp {rem:e}, 1",
+                "jb 11f",
+                "mov {buf:l}, byte ptr [{src} + {rem} - 1]",
+                "mov byte ptr [{dest} + {rem} - 1], {buf:l}",
+                "11:",
+                src = in(reg) src,
+                dest = in(reg) dest,
+                rem = inout(reg) rem => _,
+                buf = out(reg) _,
+                options(nostack),
+            );
+        }
+        /*
+        for i in 0..new_bytes.len() {
+            unsafe {
+                buf.as_mut_ptr().offset(buf.len() as isize).offset(i as isize).write_volatile(new_bytes[i]);
+            }
+        }
+        */
+
+        Ok(())
+    }
+    /// write a u8 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    #[inline(always)]
+    fn write_u8(&mut self, mut v: u8) -> Result<(), core::fmt::Error> {
+        if v == 0 {
+            return self.write_fixed_size("0");
+        }
+        // we can fairly easily predict the size of a formatted string here with lzcnt, which also
+        // means we can write directly into the correct offsets of the output string.
+        let printed_size = ((8 - v.leading_zeros() + 3) >> 2) as usize;
+
+        self.reserve(printed_size);
+
+        let buf = unsafe { self.as_mut_vec() };
+        let new_len = buf.len() + printed_size;
+
+        unsafe {
+            buf.set_len(new_len);
+        }
+        let mut p = unsafe { buf.as_mut_ptr().offset(new_len as isize) };
+
+        loop {
+            let digit = v % 16;
+            let c = c_to_hex(digit as u8);
+            unsafe {
+                p = p.offset(-1);
+                p.write(c);
+            }
+            v = v / 16;
+            if v == 0 {
+                break;
+            }
+        }
+
+        Ok(())
+    }
+    /// write a u16 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    #[inline(always)]
+    fn write_u16(&mut self, mut v: u16) -> Result<(), core::fmt::Error> {
+        if v == 0 {
+            return self.write_fixed_size("0");
+        }
+        // we can fairly easily predict the size of a formatted string here with lzcnt, which also
+        // means we can write directly into the correct offsets of the output string.
+        let printed_size = ((16 - v.leading_zeros() + 3) >> 2) as usize;
+
+        self.reserve(printed_size);
+
+        let buf = unsafe { self.as_mut_vec() };
+        let new_len = buf.len() + printed_size;
+
+        unsafe {
+            buf.set_len(new_len);
+        }
+        let mut p = unsafe { buf.as_mut_ptr().offset(new_len as isize) };
+
+        loop {
+            let digit = v % 16;
+            let c = c_to_hex(digit as u8);
+            unsafe {
+                p = p.offset(-1);
+                p.write(c);
+            }
+            v = v / 16;
+            if v == 0 {
+                break;
+            }
+        }
+
+        Ok(())
+    }
+    /// write a u32 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    #[inline(always)]
+    fn write_u32(&mut self, mut v: u32) -> Result<(), core::fmt::Error> {
+        if v == 0 {
+            return self.write_fixed_size("0");
+        }
+        // we can fairly easily predict the size of a formatted string here with lzcnt, which also
+        // means we can write directly into the correct offsets of the output string.
+        let printed_size = ((32 - v.leading_zeros() + 3) >> 2) as usize;
+
+        self.reserve(printed_size);
+
+        let buf = unsafe { self.as_mut_vec() };
+        let new_len = buf.len() + printed_size;
+
+        unsafe {
+            buf.set_len(new_len);
+        }
+        let mut p = unsafe { buf.as_mut_ptr().offset(new_len as isize) };
+
+        loop {
+            let digit = v % 16;
+            let c = c_to_hex(digit as u8);
+            unsafe {
+                p = p.offset(-1);
+                p.write(c);
+            }
+            v = v / 16;
+            if v == 0 {
+                break;
+            }
+        }
+
+        Ok(())
+    }
+    /// write a u64 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    #[inline(always)]
+    fn write_u64(&mut self, mut v: u64) -> Result<(), core::fmt::Error> {
+        if v == 0 {
+            return self.write_fixed_size("0");
+        }
+        // we can fairly easily predict the size of a formatted string here with lzcnt, which also
+        // means we can write directly into the correct offsets of the output string.
+        let printed_size = ((64 - v.leading_zeros() + 3) >> 2) as usize;
+
+        self.reserve(printed_size);
+
+        let buf = unsafe { self.as_mut_vec() };
+        let new_len = buf.len() + printed_size;
+
+        unsafe {
+            buf.set_len(new_len);
+        }
+        let mut p = unsafe { buf.as_mut_ptr().offset(new_len as isize) };
+
+        loop {
+            let digit = v % 16;
+            let c = c_to_hex(digit as u8);
+            unsafe {
+                p = p.offset(-1);
+                p.write(c);
+            }
+            v = v / 16;
+            if v == 0 {
+                break;
+            }
+        }
+
+        Ok(())
+    }
+    fn span_start(&mut self, _ty: TokenType) {}
+    fn span_end(&mut self, _ty: TokenType) {}
+}
+
+impl<'buf> DisplaySink for InstructionTextSink<'buf> {
+    #[inline(always)]
+    fn write_fixed_size(&mut self, s: &str) -> Result<(), core::fmt::Error> {
+        let buf = unsafe { self.buf.as_mut_vec() };
+        let new_bytes = s.as_bytes();
+
+        if new_bytes.len() == 0 {
+            return Ok(());
+        }
+
+        if new_bytes.len() >= 16 {
+            unsafe { unreachable_kinda_unchecked() }
+        }
+
+        unsafe {
+            let dest = buf.as_mut_ptr().offset(buf.len() as isize);
+
+            // this used to be enough to bamboozle llvm away from
+            // https://github.com/rust-lang/rust/issues/92993#issuecomment-2028915232https://github.com/rust-lang/rust/issues/92993#issuecomment-2028915232
+            // if `s` is not fixed size. somewhere between Rust 1.68 and Rust 1.74 this stopped
+            // being sufficient, so `write_fixed_size` truly should only be used for fixed size `s`
+            // (otherwise this is a libc memcpy call in disguise). for fixed-size strings this
+            // unrolls into some kind of appropriate series of `mov`.
+            dest.offset(0 as isize).write(new_bytes[0]);
+            for i in 1..new_bytes.len() {
+                dest.offset(i as isize).write(new_bytes[i]);
+            }
+
+            buf.set_len(buf.len() + new_bytes.len());
+        }
+
+        Ok(())
+    }
+    unsafe fn write_lt_32(&mut self, s: &str) -> Result<(), fmt::Error> {
+        // SAFETY: todo
+        let buf = unsafe { self.buf.as_mut_vec() };
+        let new_bytes = s.as_bytes();
+
+        // should get DCE
+        if new_bytes.len() >= 32 {
+            unsafe { core::hint::unreachable_unchecked() }
+        }
+
+        unsafe {
+            let dest = buf.as_mut_ptr().offset(buf.len() as isize);
+            let src = new_bytes.as_ptr();
+
+            let rem = new_bytes.len() as isize;
+
+            // set_len early because there is no way to avoid the following asm!() writing that
+            // same number of bytes into buf
+            buf.set_len(buf.len() + new_bytes.len());
+
+            core::arch::asm!(
+                "6:",
+                "cmp {rem:e}, 16",
+                "jb 7f",
+                "mov {buf:r}, qword ptr [{src} + {rem} - 16]",
+                "mov qword ptr [{dest} + {rem} - 16], {buf:r}",
+                "mov {buf:r}, qword ptr [{src} + {rem} - 8]",
+                "mov qword ptr [{dest} + {rem} - 8], {buf:r}",
+                "sub {rem:e}, 16",
+                "jz 11f",
+                "7:",
+                "cmp {rem:e}, 8",
+                "jb 8f",
+                "mov {buf:r}, qword ptr [{src} + {rem} - 8]",
+                "mov qword ptr [{dest} + {rem} - 8], {buf:r}",
+                "sub {rem:e}, 8",
+                "jz 11f",
+                "8:",
+                "cmp {rem:e}, 4",
+                "jb 9f",
+                "mov {buf:e}, dword ptr [{src} + {rem} - 4]",
+                "mov dword ptr [{dest} + {rem} - 4], {buf:e}",
+                "sub {rem:e}, 4",
+                "jz 11f",
+                "9:",
+                "cmp {rem:e}, 2",
+                "jb 10f",
+                "mov {buf:x}, word ptr [{src} + {rem} - 2]",
+                "mov word ptr [{dest} + {rem} - 2], {buf:x}",
+                "sub {rem:e}, 2",
+                "jz 11f",
+                "10:",
+                "cmp {rem:e}, 1",
+                "jb 11f",
+                "mov {buf:l}, byte ptr [{src} + {rem} - 1]",
+                "mov byte ptr [{dest} + {rem} - 1], {buf:l}",
+                "11:",
+                src = in(reg) src,
+                dest = in(reg) dest,
+                rem = inout(reg) rem => _,
+                buf = out(reg) _,
+                options(nostack),
+            );
+        }
+        /*
+        for i in 0..new_bytes.len() {
+            unsafe {
+                buf.as_mut_ptr().offset(buf.len() as isize).offset(i as isize).write_volatile(new_bytes[i]);
+            }
+        }
+        */
+
+        Ok(())
+    }
+    unsafe fn write_lt_16(&mut self, s: &str) -> Result<(), fmt::Error> {
+        // SAFETY: todo
+        let buf = unsafe { self.buf.as_mut_vec() };
+        let new_bytes = s.as_bytes();
+
+        // should get DCE
+        if new_bytes.len() >= 16 {
+            unsafe { core::hint::unreachable_unchecked() }
+        }
+
+        unsafe {
+            let dest = buf.as_mut_ptr().offset(buf.len() as isize);
+            let src = new_bytes.as_ptr();
+
+            let rem = new_bytes.len() as isize;
+
+            // set_len early because there is no way to avoid the following asm!() writing that
+            // same number of bytes into buf
+            buf.set_len(buf.len() + new_bytes.len());
+
+            core::arch::asm!(
+                "7:",
+                "cmp {rem:e}, 8",
+                "jb 8f",
+                "mov {buf:r}, qword ptr [{src} + {rem} - 8]",
+                "mov qword ptr [{dest} + {rem} - 8], {buf:r}",
+                "sub {rem:e}, 8",
+                "jz 11f",
+                "8:",
+                "cmp {rem:e}, 4",
+                "jb 9f",
+                "mov {buf:e}, dword ptr [{src} + {rem} - 4]",
+                "mov dword ptr [{dest} + {rem} - 4], {buf:e}",
+                "sub {rem:e}, 4",
+                "jz 11f",
+                "9:",
+                "cmp {rem:e}, 2",
+                "jb 10f",
+                "mov {buf:x}, word ptr [{src} + {rem} - 2]",
+                "mov word ptr [{dest} + {rem} - 2], {buf:x}",
+                "sub {rem:e}, 2",
+                "jz 11f",
+                "10:",
+                "cmp {rem:e}, 1",
+                "jb 11f",
+                "mov {buf:l}, byte ptr [{src} + {rem} - 1]",
+                "mov byte ptr [{dest} + {rem} - 1], {buf:l}",
+                "11:",
+                src = in(reg) src,
+                dest = in(reg) dest,
+                rem = inout(reg) rem => _,
+                buf = out(reg) _,
+                options(nostack),
+            );
+        }
+        /*
+        for i in 0..new_bytes.len() {
+            unsafe {
+                buf.as_mut_ptr().offset(buf.len() as isize).offset(i as isize).write_volatile(new_bytes[i]);
+            }
+        }
+        */
+
+        Ok(())
+    }
+    unsafe fn write_lt_8(&mut self, s: &str) -> Result<(), fmt::Error> {
+        // SAFETY: todo
+        let buf = unsafe { self.buf.as_mut_vec() };
+        let new_bytes = s.as_bytes();
+
+        // should get DCE
+        if new_bytes.len() >= 8 {
+            unsafe { core::hint::unreachable_unchecked() }
+        }
+
+        unsafe {
+            let dest = buf.as_mut_ptr().offset(buf.len() as isize);
+            let src = new_bytes.as_ptr();
+
+            let rem = new_bytes.len() as isize;
+
+            // set_len early because there is no way to avoid the following asm!() writing that
+            // same number of bytes into buf
+            buf.set_len(buf.len() + new_bytes.len());
+
+            core::arch::asm!(
+                "8:",
+                "cmp {rem:e}, 4",
+                "jb 9f",
+                "mov {buf:e}, dword ptr [{src} + {rem} - 4]",
+                "mov dword ptr [{dest} + {rem} - 4], {buf:e}",
+                "sub {rem:e}, 4",
+                "jz 11f",
+                "9:",
+                "cmp {rem:e}, 2",
+                "jb 10f",
+                "mov {buf:x}, word ptr [{src} + {rem} - 2]",
+                "mov word ptr [{dest} + {rem} - 2], {buf:x}",
+                "sub {rem:e}, 2",
+                "jz 11f",
+                "10:",
+                "cmp {rem:e}, 1",
+                "jb 11f",
+                "mov {buf:l}, byte ptr [{src} + {rem} - 1]",
+                "mov byte ptr [{dest} + {rem} - 1], {buf:l}",
+                "11:",
+                src = in(reg) src,
+                dest = in(reg) dest,
+                rem = inout(reg) rem => _,
+                buf = out(reg) _,
+                options(nostack),
+            );
+        }
+        /*
+        for i in 0..new_bytes.len() {
+            unsafe {
+                buf.as_mut_ptr().offset(buf.len() as isize).offset(i as isize).write_volatile(new_bytes[i]);
+            }
+        }
+        */
+
+        Ok(())
+    }
+    /// write a u8 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    #[inline(always)]
+    fn write_u8(&mut self, mut v: u8) -> Result<(), core::fmt::Error> {
+        if v == 0 {
+            return self.write_fixed_size("0");
+        }
+        // we can fairly easily predict the size of a formatted string here with lzcnt, which also
+        // means we can write directly into the correct offsets of the output string.
+        let printed_size = ((8 - v.leading_zeros() + 3) >> 2) as usize;
+
+        let buf = unsafe { self.buf.as_mut_vec() };
+        let new_len = buf.len() + printed_size;
+
+        unsafe {
+            buf.set_len(new_len);
+        }
+        let mut p = unsafe { buf.as_mut_ptr().offset(new_len as isize) };
+
+        loop {
+            let digit = v % 16;
+            let c = c_to_hex(digit as u8);
+            unsafe {
+                p = p.offset(-1);
+                p.write(c);
+            }
+            v = v / 16;
+            if v == 0 {
+                break;
+            }
+        }
+
+        Ok(())
+    }
+    /// write a u16 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    #[inline(always)]
+    fn write_u16(&mut self, mut v: u16) -> Result<(), core::fmt::Error> {
+        if v == 0 {
+            return self.write_fixed_size("0");
+        }
+        // we can fairly easily predict the size of a formatted string here with lzcnt, which also
+        // means we can write directly into the correct offsets of the output string.
+        let printed_size = ((16 - v.leading_zeros() + 3) >> 2) as usize;
+
+        let buf = unsafe { self.buf.as_mut_vec() };
+        let new_len = buf.len() + printed_size;
+
+        unsafe {
+            buf.set_len(new_len);
+        }
+        let mut p = unsafe { buf.as_mut_ptr().offset(new_len as isize) };
+
+        loop {
+            let digit = v % 16;
+            let c = c_to_hex(digit as u8);
+            unsafe {
+                p = p.offset(-1);
+                p.write(c);
+            }
+            v = v / 16;
+            if v == 0 {
+                break;
+            }
+        }
+
+        Ok(())
+    }
+    /// write a u32 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    #[inline(always)]
+    fn write_u32(&mut self, mut v: u32) -> Result<(), core::fmt::Error> {
+        if v == 0 {
+            return self.write_fixed_size("0");
+        }
+        // we can fairly easily predict the size of a formatted string here with lzcnt, which also
+        // means we can write directly into the correct offsets of the output string.
+        let printed_size = ((32 - v.leading_zeros() + 3) >> 2) as usize;
+
+        let buf = unsafe { self.buf.as_mut_vec() };
+        let new_len = buf.len() + printed_size;
+
+        unsafe {
+            buf.set_len(new_len);
+        }
+        let mut p = unsafe { buf.as_mut_ptr().offset(new_len as isize) };
+
+        loop {
+            let digit = v % 16;
+            let c = c_to_hex(digit as u8);
+            unsafe {
+                p = p.offset(-1);
+                p.write(c);
+            }
+            v = v / 16;
+            if v == 0 {
+                break;
+            }
+        }
+
+        Ok(())
+    }
+    /// write a u64 to the output as a base-16 integer.
+    ///
+    /// this is provided for optimization opportunities when the formatted integer can be written
+    /// directly to the sink (rather than formatted to an intermediate buffer and output as a
+    /// followup step)
+    #[inline(always)]
+    fn write_u64(&mut self, mut v: u64) -> Result<(), core::fmt::Error> {
+        if v == 0 {
+            return self.write_fixed_size("0");
+        }
+        // we can fairly easily predict the size of a formatted string here with lzcnt, which also
+        // means we can write directly into the correct offsets of the output string.
+        let printed_size = ((64 - v.leading_zeros() + 3) >> 2) as usize;
+
+        let buf = unsafe { self.buf.as_mut_vec() };
+        let new_len = buf.len() + printed_size;
+
+        unsafe {
+            buf.set_len(new_len);
+        }
+        let mut p = unsafe { buf.as_mut_ptr().offset(new_len as isize) };
+
+        loop {
+            let digit = v % 16;
+            let c = c_to_hex(digit as u8);
+            unsafe {
+                p = p.offset(-1);
+                p.write(c);
+            }
+            v = v / 16;
+            if v == 0 {
+                break;
+            }
+        }
+
+        Ok(())
+    }
+    fn span_start(&mut self, _ty: TokenType) {}
+    fn span_end(&mut self, _ty: TokenType) {}
+}