Add support for libc::readv

- This enables vectorized reads.

Signed-off-by: shamb0 <[email protected]>

src/shims/files.rs

@@ -29,6 +29,21 @@ pub trait FileDescription: std::fmt::Debug + Any {
         throw_unsup_format!("cannot read from {}", self.name());
     }
 
+    /// Reads data directly into a byte buffer without using Miri's pointer abstraction.
+    /// This function provides an alternative to `read()` that works with byte slices,
+    /// making it particularly suitable for operations requiring atomic reads or
+    /// direct buffer manipulation.
+    fn read_buffer<'tcx>(
+        &self,
+        _self_ref: &FileDescriptionRef,
+        _communicate_allowed: bool,
+        _buf: &mut [u8],
+        _dest: &MPlaceTy<'tcx>,
+        _ecx: &mut MiriInterpCx<'tcx>,
+    ) -> InterpResult<'tcx> {
+        throw_unsup_format!("cannot read from {}", self.name());
+    }
+
     /// Writes as much as possible from the given buffer `ptr`.
     /// `len` indicates how many bytes we should try to write.
     /// `dest` is where the return value should be stored: number of bytes written, or `-1` in case of error.

src/shims/unix/fd.rs

@@ -5,6 +5,7 @@ use std::io;
 use std::io::ErrorKind;
 
 use rustc_abi::Size;
+use rustc_middle::ty::layout::TyAndLayout;
 
 use crate::helpers::check_min_arg_count;
 use crate::shims::files::FileDescription;
@@ -257,6 +258,248 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         interp_ok(())
     }
 
+    /// Reads data from a file descriptor into multiple buffers atomically (vectored I/O).
+    ///
+    /// This implementation follows POSIX readv() semantics, reading data from the file descriptor
+    /// specified by `fd_num` into the buffers described by the array of iovec structures pointed
+    /// to by `iov_ptr`. The `iovcnt` argument specifies the number of iovec structures in the array.
+    ///
+    /// # Arguments
+    /// * `fd_num` - The file descriptor to read from
+    /// * `iov_ptr` - Pointer to an array of iovec structures
+    /// * `iovcnt` - Number of iovec structures in the array
+    /// * `dest` - Destination for storing the number of bytes read
+    ///
+    /// # Returns
+    /// * `Ok(())` - Operation completed successfully, with total bytes read stored in `dest`
+    /// * `Err(_)` - Operation failed with appropriate errno set
+    ///
+    /// # Errors
+    /// * `EBADF` - `fd_num` is not a valid file descriptor
+    /// * `EFAULT` - Part of iovec array or buffers point outside accessible address space
+    /// * `EINVAL` - `iovcnt` is negative or exceeds system limit
+    /// * `EIO` - I/O error occurred while reading from the file descriptor
+    ///
+    /// # POSIX Compliance
+    /// Implements standard POSIX readv() behavior:
+    /// * Performs reads atomically with respect to other threads
+    /// * Returns exact number of bytes read or -1 on error
+    /// * Handles partial reads and end-of-file conditions
+    /// * Respects system-imposed limits on total transfer size
+    fn readv(
+        &mut self,
+        fd_num: i32,
+        iov_ptr: &OpTy<'tcx>,
+        iovcnt: i32,
+        dest: &MPlaceTy<'tcx>,
+    ) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+
+        // POSIX Compliance: Must handle negative values (EINVAL).
+        if iovcnt < 0 {
+            return this.set_last_error_and_return(LibcError("EINVAL"), dest);
+        }
+
+        // POSIX Compliance: Must handle zero properly.
+        if iovcnt == 0 {
+            return this.write_scalar(Scalar::from_i32(0), dest);
+        }
+
+        // POSIX Compliance: Check if iovcnt exceeds system limits.
+        // Most implementations limit this to IOV_MAX
+        // Common system default
+        // https://github.com/turbolent/w2c2/blob/d94227c22f8d78a04fbad70fa744481ca4a1912e/examples/clang/sys/include/limits.h#L50
+        const IOV_MAX: i32 = 1024;
+        if iovcnt > IOV_MAX {
+            trace!("readv: iovcnt exceeds IOV_MAX");
+            return this.set_last_error_and_return(LibcError("EINVAL"), dest);
+        }
+
+        // POSIX Compliance: Validate file descriptor.
+        let Some(fd) = this.machine.fds.get(fd_num) else {
+            return this.set_last_error_and_return(LibcError("EBADF"), dest);
+        };
+
+        // Convert iovcnt to usize for array indexing.
+        let iovcnt = usize::try_from(iovcnt).expect("iovcnt exceeds platform size");
+        let iovec_layout = this.libc_ty_layout("iovec");
+
+        // Gather iovec information.
+        // Pre-allocate vectors for iovec information
+        let mut iov_info = Vec::with_capacity(iovcnt);
+        let mut total_size: u64 = 0;
+
+        // POSIX Compliance: Validate each iovec structure.
+        // Must check for EFAULT (invalid buffer addresses) and EINVAL (invalid length).
+        for i in 0..iovcnt {
+            // Calculate offset to current iovec structure.
+            let offset = iovec_layout
+                .size
+                .bytes()
+                .checked_mul(i as u64)
+                .expect("iovec array index overflow");
+
+            // Access current iovec structure.
+            let current_iov = match this
+                .deref_pointer_and_offset_vectored(
+                    iov_ptr,
+                    offset,
+                    iovec_layout,
+                    iovcnt,
+                    iovec_layout,
+                )
+                .report_err()
+            {
+                Ok(iov) => iov,
+                Err(_) => {
+                    return this.set_last_error_and_return(LibcError("EFAULT"), dest);
+                }
+            };
+
+            // Extract and validate buffer pointer and length.
+            let base_field = this.project_field_named(&current_iov, "iov_base")?;
+            let base = this.read_pointer(&base_field)?;
+
+            let len_field = this.project_field_named(&current_iov, "iov_len")?;
+            let len = this.read_target_usize(&len_field)?;
+
+            // Validate buffer alignment and accessibility.
+            if this
+                .check_ptr_access(base, Size::from_bytes(len), CheckInAllocMsg::MemoryAccessTest)
+                .report_err()
+                .is_err()
+            {
+                return this.set_last_error_and_return(LibcError("EFAULT"), dest);
+            }
+
+            // Update total size safely.
+            total_size = match total_size.checked_add(len) {
+                Some(new_size) => new_size,
+                None => {
+                    return this.set_last_error_and_return(LibcError("EINVAL"), dest);
+                }
+            };
+
+            iov_info.push((base, len));
+        }
+
+        // Cap total size to platform limits.
+        let total_size =
+            total_size.min(u64::try_from(this.target_isize_max()).unwrap()).min(isize::MAX as u64);
+
+        // Early return for zero total size
+        if total_size == 0 {
+            return this.write_scalar(Scalar::from_i32(0), dest);
+        }
+
+        let mut temp_buf: Vec<u8> = vec![0; total_size.try_into().unwrap()];
+
+        // Perform single atomic read operation
+        let read_result =
+            fd.read_buffer(&fd, this.machine.communicate(), &mut temp_buf[..], dest, this);
+
+        // Handle read result
+        if read_result.report_err().is_err() {
+            return this.set_last_error_and_return(LibcError("EIO"), dest);
+        }
+
+        // Get bytes read from dest and convert to usize for slice operations.
+        let read_bytes = usize::try_from(this.read_scalar(dest)?.to_u64()?)
+            .expect("read bytes count exceeds platform size");
+
+        if read_bytes > 0 {
+            // Copy data to individual iovec buffers.
+            let mut current_pos = 0usize;
+
+            for (base, len) in iov_info {
+                // Early exit if no more bytes to copy.
+                if current_pos >= read_bytes {
+                    break;
+                }
+
+                // Convert len to usize safely and handle potential overflow.
+                let buffer_len = usize::try_from(len).expect("buffer length exceeds platform size");
+
+                // Calculate remaining bytes safely.
+                let bytes_remaining =
+                    read_bytes.checked_sub(current_pos).expect("position calculation underflow");
+
+                // Calculate copy size as minimum of buffer length and remaining bytes.
+                let copy_size = buffer_len.min(bytes_remaining);
+
+                // Calculate end position safely.
+                let slice_end =
+                    current_pos.checked_add(copy_size).expect("slice end calculation overflow");
+
+                // Verify slice bounds.
+                if slice_end > temp_buf.len() {
+                    return this.set_last_error_and_return(LibcError("EFAULT"), dest);
+                }
+
+                // Write the slice to the destination buffer.
+                if this
+                    .write_bytes_ptr(base, temp_buf[current_pos..slice_end].iter().copied())
+                    .report_err()
+                    .is_err()
+                {
+                    return this.set_last_error_and_return(LibcError("EIO"), dest);
+                }
+
+                // Update position safely.
+                current_pos = slice_end;
+            }
+        }
+
+        interp_ok(())
+    }
+
+    /// Dereferences a pointer to access an element within a source array, with specialized bounds checking
+    /// for vectored I/O operations like readv().
+    ///
+    /// This function provides array-aware bounds checking that is specifically designed for situations
+    /// where we need to access multiple independent memory regions, such as when processing an array
+    /// of iovec structures. Unlike simple pointer arithmetic bounds checking, this implementation
+    /// understands and validates array-based access patterns.
+    fn deref_pointer_and_offset_vectored(
+        &self,
+        op: &impl Projectable<'tcx, Provenance>,
+        offset_bytes: u64,
+        base_layout: TyAndLayout<'tcx>,
+        count: usize,
+        value_layout: TyAndLayout<'tcx>,
+    ) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
+        // 1. Validate the iovec array bounds.
+        let array_size = base_layout
+            .size
+            .bytes()
+            .checked_mul(count as u64)
+            .ok_or_else(|| err_ub_format!("iovec array size overflow"))?;
+
+        // 2. Check if our offset is within the array.
+        if offset_bytes >= array_size {
+            throw_ub_format!(
+                "{}",
+                format!(
+                    "iovec array access out of bounds: offset {} in array of size {}",
+                    offset_bytes, array_size
+                )
+            );
+        }
+
+        // 3. Ensure the iovec structure we're accessing is fully contained.
+        if offset_bytes.checked_add(base_layout.size.bytes()).is_none_or(|end| end > array_size) {
+            throw_ub_format!("iovec structure would extend past array bounds");
+        }
+
+        // 4. Proceed with the dereferencing.
+        let this = self.eval_context_ref();
+        let op_place = this.deref_pointer_as(op, base_layout)?;
+        let offset = Size::from_bytes(offset_bytes);
+
+        let value_place = op_place.offset(offset, value_layout, this)?;
+        interp_ok(value_place)
+    }
+
     fn write(
         &mut self,
         fd_num: i32,

src/shims/unix/foreign_items.rs

@@ -157,6 +157,12 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 let count = this.read_target_usize(count)?;
                 this.read(fd, buf, count, None, dest)?;
             }
+            "readv" => {
+                let [fd, iov, iovcnt] = this.check_shim(abi, ExternAbi::C { unwind: false }, link_name, args)?;
+                let fd = this.read_scalar(fd)?.to_i32()?;
+                let iovcnt = this.read_scalar(iovcnt)?.to_i32()?;
+                this.readv(fd, iov, iovcnt, dest)?;
+            }
             "write" => {
                 let [fd, buf, n] = this.check_shim(abi, ExternAbi::C { unwind: false }, link_name, args)?;
                 let fd = this.read_scalar(fd)?.to_i32()?;

src/shims/unix/fs.rs

@@ -48,6 +48,37 @@ impl FileDescription for FileHandle {
         }
     }
 
+    /// Reads data directly into a byte buffer without using Miri's pointer abstraction.
+    /// This function provides an alternative to `read()` that works with byte slices,
+    /// making it particularly suitable for operations requiring atomic reads or
+    /// direct buffer manipulation.
+    fn read_buffer<'tcx>(
+        &self,
+        _self_ref: &FileDescriptionRef,
+        communicate_allowed: bool,
+        buf: &mut [u8],
+        dest: &MPlaceTy<'tcx>,
+        ecx: &mut MiriInterpCx<'tcx>,
+    ) -> InterpResult<'tcx> {
+        let this = ecx.eval_context_mut();
+
+        // Check isolation mode
+        if !communicate_allowed {
+            helpers::isolation_abort_error("`read` operation")?;
+        }
+
+        // Perform read operation
+        let result = (&mut &self.file).read(buf);
+
+        match result {
+            Ok(read_size) => {
+                this.write_int(u64::try_from(read_size).unwrap(), dest)?;
+                interp_ok(())
+            }
+            Err(e) => this.set_last_error_and_return(e, dest),
+        }
+    }
+
     fn write<'tcx>(
         &self,
         _self_ref: &FileDescriptionRef,