rustc-demangle-capi/src/lib.rs

extern crate rustc_demangle;

use std::alloc::{GlobalAlloc, Layout, System};
use std::io::Write;
use std::os::raw::{c_char, c_int};
use std::ptr;
use std::result;

type Result<T> = result::Result<T, Status>;

/// Convenience function to set return status if a location was provided.
unsafe fn set_status(status: *mut c_int, val: c_int) {
    if !status.is_null() {
        *status = val;
    }
}

/// Region from the system allocator for demangler output. We use the
/// system allocator because the intended client is C/C++ code which
/// may not be using the Rust allocator.
struct SystemBuffer {
    buf: *mut u8,
    size: usize,
    size_out: *mut usize,
}

impl SystemBuffer {
    const DEFAULT_BUFFER_SIZE: usize = 1024;
    fn new(size: usize) -> Result<Self> {
        let buf = unsafe { System.alloc_zeroed(Layout::from_size_align_unchecked(size, 1)) };
        if buf.is_null() {
            Err(Status::AllocFailure)
        } else {
            Ok(Self {
                buf,
                size,
                size_out: ptr::null_mut(),
            })
        }
    }
    /// Safety: If buf is non-null, size must be non-null and point to the
    /// non-zero size of the buffer provided in buf.
    /// Takes ownership of the buffer passed in (and may reallocate it).
    /// size must outlive the resulting buffer if non-null.
    unsafe fn from_raw(buf: *mut c_char, size: *mut usize) -> Result<Self> {
        if buf.is_null() {
            if !size.is_null() {
                *size = Self::DEFAULT_BUFFER_SIZE;
            }
            let fresh = Self::new(Self::DEFAULT_BUFFER_SIZE)?;
            Ok(Self {
                size_out: size,
                ..fresh
            })
        } else {
            Ok(Self {
                buf: buf as *mut u8,
                size: *size,
                size_out: size,
            })
        }
    }
    fn as_mut_slice(&mut self) -> &mut [u8] {
        unsafe { std::slice::from_raw_parts_mut(self.buf, self.size) }
    }
    fn resize(&mut self) -> Result<()> {
        let new_size = self.size * 2;
        let new_buf = unsafe {
            System.realloc(
                self.buf,
                Layout::from_size_align_unchecked(self.size, 1),
                new_size,
            )
        };
        if new_buf.is_null() {
            Err(Status::AllocFailure)
        } else {
            self.buf = new_buf;
            self.size = new_size;
            if !self.size_out.is_null() {
                unsafe {
                    *self.size_out = new_size;
                }
            }
            Ok(())
        }
    }
}

/// C-style interface for demangling.
/// Demangles symbol given in `mangled` argument into `out` buffer.
///
/// This interface is a drop-in replacement for `__cxa_demangle`, but for
/// Rust demangling.
///
/// If `out` is null, a buffer will be allocated using the system allocator
/// to contain the results.
/// If `out` is non-null, `out_size` must be a pointer to the current size
/// of the buffer, and `out` must come from the system allocator.
/// If `out_size` is non-null, the size of the output buffer will be written
/// to it.
///
/// If `status` is non-null, it will be set to one of the following values:
/// * 0: Demangling succeeded
/// * -1: Allocation failure
/// * -2: Name did not demangle
/// * -3: Invalid arguments
///
/// Returns null if `mangled` is not Rust symbol or demangling failed.
/// Returns the buffer containing the demangled symbol name otherwise.
///
/// Unsafe as it handles buffers by raw pointers.
///
/// For non-null `out`, `out_size` represents a slight deviation from the
/// `__cxa_demangle` behavior. For `__cxa_demangle`, the buffer must be at
/// *least* the provided size. For `rustc_demangle`, it must be the exact
/// buffer size because it is used in the reconstruction of the `Layout`
/// for use with `::realloc`.
#[no_mangle]
pub unsafe extern "C" fn rustc_demangle(
    mangled: *const c_char,
    out: *mut c_char,
    out_size: *mut usize,
    status: *mut c_int,
) -> *mut c_char {
    match rustc_demangle_native(mangled, out, out_size) {
        Ok(demangled) => {
            set_status(status, 0);
            demangled
        }
        Err(e) => {
            set_status(status, e as c_int);
            ptr::null_mut()
        }
    }
}

enum Status {
    AllocFailure = -1,
    DemangleFailure = -2,
    InvalidArgs = -3,
}

unsafe fn rustc_demangle_native(
    mangled: *const c_char,
    out: *mut c_char,
    out_size: *mut usize,
) -> Result<*mut c_char> {
    if mangled.is_null() {
        return Err(Status::InvalidArgs);
    }
    let mangled_str = match std::ffi::CStr::from_ptr(mangled).to_str() {
        Ok(s) => s,
        Err(_) => return Err(Status::InvalidArgs),
    };

    if !out.is_null() {
        if out_size.is_null() {
            return Err(Status::InvalidArgs);
        }
        if *out_size == 0 {
            return Err(Status::InvalidArgs);
        }
    }

    match rustc_demangle::try_demangle(mangled_str) {
        Ok(demangle) => {
            let mut out_buf = SystemBuffer::from_raw(out, out_size)?;
            while write!(out_buf.as_mut_slice(), "{:#}\0", demangle).is_err() {
                out_buf.resize()?;
            }
            Ok(out_buf.as_mut_slice().as_mut_ptr() as *mut c_char)
        }
        Err(_) => Err(Status::DemangleFailure),
    }
}

#[cfg(test)]
mod tests {
    use std::alloc::{GlobalAlloc, Layout, System};
    use std::os::raw::{c_char, c_int};
    use std::ptr;

    struct DemangleResult {
        out_buf: *mut u8,
        out_size: usize,
        status: c_int,
    }

    impl Drop for DemangleResult {
        fn drop(&mut self) {
            if !self.out_buf.is_null() {
                unsafe {
                    System.dealloc(
                        self.out_buf,
                        Layout::from_size_align_unchecked(self.out_size, 1),
                    );
                }
            }
        }
    }

    impl DemangleResult {
        fn as_slice(&self) -> &[u8] {
            unsafe { std::slice::from_raw_parts(self.out_buf, self.out_size) }
        }
    }

    fn demangle(mangled: &str, alloc_size: usize) -> DemangleResult {
        unsafe { raw_demangle(mangled.as_ptr() as *const c_char, alloc_size) }
    }

    unsafe fn raw_demangle(mangled: *const c_char, alloc_size: usize) -> DemangleResult {
        let mut out_size: usize = alloc_size;
        let mut status: c_int = 0;
        let out_buf: *mut c_char = if out_size != 0 {
            System.alloc(Layout::from_size_align_unchecked(out_size, 1)) as *mut c_char
        } else {
            ptr::null_mut()
        };
        ptr::write_bytes(out_buf, '*' as u8, out_size);

        let res = super::rustc_demangle(mangled, out_buf, &mut out_size, &mut status);
        DemangleResult {
            out_buf: res as *mut u8,
            out_size,
            status,
        }
    }

    #[test]
    fn demangle_c_str_large() {
        let res = demangle("_ZN4testE\0", 8);
        assert_eq!(res.status, 0);
        let out_str = core::str::from_utf8(&res.as_slice()[..5]).unwrap();
        assert_eq!(out_str, "test\0");
    }

    #[test]
    fn demangle_c_str_exact() {
        let res = demangle("_ZN4testE\0", 8);
        assert_eq!(res.status, 0);
        // No reallocation necessary, so our * fill should be present
        let out_str = core::str::from_utf8(res.as_slice()).unwrap();
        assert_eq!(out_str, "test\0***");
    }

    #[test]
    fn demangle_c_str_small() {
        let res = demangle("_ZN4testE\0", 4);
        assert_eq!(res.status, 0);
        // demangle should have realloced
        assert_ne!(res.out_size, 4);
        // Only check the start, since the reallocation means our * fill may
        // be absent.
        let out_str = core::str::from_utf8(&res.as_slice()[..5]).unwrap();
        assert_eq!(out_str, "test\0");
    }

    #[test]
    fn demangle_c_str_alloc() {
        let res = demangle("_ZN4testE\0", 0);
        assert_eq!(res.status, 0);
        // demangle should have allocated
        assert_ne!(res.out_size, 0);
        let out_str = core::str::from_utf8(&res.as_slice()[..5]).unwrap();
        assert_eq!(out_str, "test\0");
    }

    #[test]
    fn demangle_c_str_not_rust_symbol() {
        let res = demangle("la la la\0", 8);
        assert_eq!(res.status, -2);
    }

    #[test]
    fn demangle_c_str_null() {
        let res = demangle("\0", 8);
        assert_eq!(res.status, -2);
    }

    #[test]
    fn demangle_c_str_invalid_utf8() {
        let mangled = [116, 101, 115, 116, 165, 0];
        let res = unsafe { raw_demangle(mangled.as_ptr() as *const c_char, 8) };
        assert_eq!(res.status, -2);
    }
}