build: Rust 1.39 update

- cargo: configured the build dir via `.cargo/config`;
- devctr: removed env variable used to override build dir; updated rust
  toolchain to 1.39;
- clippy: added safety doc comments;
- vsock: switched to using zeroed memory for the TX buffer, instead of
  `mem::uninitialized`, since the latter is both unsafe and deprecated
  by Rust 1.39.

Signed-off-by: Dan Horobeanu <[email protected]>

.cargo/config

@@ -1,5 +1,6 @@
 [build]
 target = "x86_64-unknown-linux-musl"
+target-dir = "build/cargo_target"
 
 [target.'cfg(any(target_arch="arm", target_arch="aarch64"))']
 # On aarch64 musl depends on some libgcc functions (i.e `__addtf3` and other `*tf3` functions) for logic that uses

src/devices/src/virtio/vsock/csm/txbuf.rs

@@ -3,7 +3,6 @@
 //
 
 use std::io::Write;
-use std::mem;
 use std::num::Wrapping;
 
 use super::defs;
@@ -14,7 +13,7 @@ use super::{Error, Result};
 /// the host can't read fast enough.
 pub struct TxBuf {
     /// The actual u8 buffer - only allocated after the first push.
-    data: Option<Box<[u8; Self::SIZE]>>,
+    data: Option<Box<[u8]>>,
     /// Ring-buffer head offset - where new data is pushed to.
     head: Wrapping<u32>,
     /// Ring-buffer tail offset - where data is flushed from.
@@ -50,17 +49,9 @@ impl TxBuf {
             return Err(Error::TxBufFull);
         }
 
-        // We're using a closure here to return the boxed slice, instead of a value (i.e.
-        // `get_or_insert_with()` instead of `get_or_insert()`), because we only want the box
-        // created when `self.data` is None. If we were to use `get_or_insert(box)`, the box
-        // argument would always get evaluated (which implies a heap allocation), even though
-        // it would later be discarded (when `self.data.is_some()`). Apparently, clippy fails
-        // to see this, and insists on issuing some warning.
-        let data = self.data.get_or_insert_with(||
-                // Using uninitialized memory here is quite safe, since we never read from any
-                // area of the buffer before writing to it. First we push, then we flush only
-                // what had been prviously pushed.
-                Box::new(unsafe {mem::uninitialized::<[u8; Self::SIZE]>()}));
+        let data = self
+            .data
+            .get_or_insert_with(|| vec![0u8; Self::SIZE].into_boxed_slice());
 
         // Buffer head, as an offset into the data slice.
         let head_ofs = self.head.0 as usize % Self::SIZE;

src/utils/src/structs.rs

@@ -26,13 +26,16 @@ impl fmt::Display for Error {
 pub type Result<T> = std::result::Result<T, Error>;
 
 /// Reads a struct from an input buffer.
-/// This is unsafe because the struct is initialized to unverified data read from the input.
-/// `read_struct` should only be called to fill plain old data structs.  It is not endian safe.
 ///
 /// # Arguments
 ///
 /// * `f` - The input to read from.  Often this is a file.
 /// * `out` - The struct to fill with data read from `f`.
+///
+/// # Safety
+///
+/// This is unsafe because the struct is initialized to unverified data read from the input.
+/// `read_struct` should only be called to fill plain old data structs.  It is not endian safe.
 pub unsafe fn read_struct<T: Copy, F: Read>(f: &mut F, out: &mut T) -> Result<()> {
     let out_slice = std::slice::from_raw_parts_mut(out as *mut T as *mut u8, mem::size_of::<T>());
     f.read_exact(out_slice).map_err(Error::ReadStruct)?;
@@ -41,15 +44,16 @@ pub unsafe fn read_struct<T: Copy, F: Read>(f: &mut F, out: &mut T) -> Result<()
 
 /// Reads an array of structs from an input buffer.  Returns a Vec of structs initialized with data
 /// from the specified input.
-/// This is unsafe because the structs are initialized to unverified data read from the input.
-/// `read_struct_slice` should only be called for plain old data structs.  It is not endian safe.
 ///
 /// # Arguments
 ///
 /// * `f` - The input to read from.  Often this is a file.
 /// * `len` - The number of structs to fill with data read from `f`.
-// This lint check is now deprecated - https://github.com/rust-lang/rust-clippy/pull/3478/files
-// we can safely allow this.
+///
+/// # Safety
+///
+/// This is unsafe because the structs are initialized to unverified data read from the input.
+/// `read_struct_slice` should only be called for plain old data structs.  It is not endian safe.
 pub unsafe fn read_struct_slice<T: Copy, F: Read>(f: &mut F, len: usize) -> Result<Vec<T>> {
     let mut out: Vec<T> = Vec::with_capacity(len);
     out.set_len(len);

tests/integration_tests/build/test_coverage.py

@@ -19,7 +19,7 @@
 
 import host_tools.cargo_build as host  # pylint: disable=import-error
 
-COVERAGE_TARGET_PCT = 84.8
+COVERAGE_TARGET_PCT = 85.2
 COVERAGE_MAX_DELTA = 0.01
 
 CARGO_KCOV_REL_PATH = os.path.join(host.CARGO_BUILD_REL_PATH, 'kcov')

tools/devctr/Dockerfile.aarch64

@@ -4,7 +4,7 @@ FROM ubuntu:18.04
 # The Rust toolchain layer will get updated most frequently, but we could keep the system
 # dependencies layer intact for much longer.
 
-ARG RUST_TOOLCHAIN="1.38.0"
+ARG RUST_TOOLCHAIN="1.39.0"
 ARG TMP_BUILD_DIR=/tmp/build
 ARG FIRECRACKER_SRC_DIR="/firecracker"
 ARG FIRECRACKER_BUILD_DIR="$FIRECRACKER_SRC_DIR/build"
@@ -14,7 +14,6 @@ ARG CARGO_GIT_REGISTRY_DIR="$FIRECRACKER_BUILD_DIR/cargo_git_registry"
 ENV CARGO_HOME=/usr/local/rust
 ENV RUSTUP_HOME=/usr/local/rust
 ENV PATH="$PATH:$CARGO_HOME/bin"
-ENV CARGO_TARGET_DIR="$FIRECRACKER_BUILD_DIR/cargo_target"
 
 # Install system dependecies
 #

tools/devctr/Dockerfile.x86_64

@@ -4,7 +4,7 @@ FROM ubuntu:18.04
 # The Rust toolchain layer will get updated most frequently, but we could keep the system
 # dependencies layer intact for much longer.
 
-ARG RUST_TOOLCHAIN="1.38.0"
+ARG RUST_TOOLCHAIN="1.39.0"
 ARG TMP_BUILD_DIR=/tmp/build
 ARG FIRECRACKER_SRC_DIR="/firecracker"
 ARG FIRECRACKER_BUILD_DIR="$FIRECRACKER_SRC_DIR/build"
@@ -14,7 +14,6 @@ ARG CARGO_GIT_REGISTRY_DIR="$FIRECRACKER_BUILD_DIR/cargo_git_registry"
 ENV CARGO_HOME=/usr/local/rust
 ENV RUSTUP_HOME=/usr/local/rust
 ENV PATH="$PATH:$CARGO_HOME/bin"
-ENV CARGO_TARGET_DIR="$FIRECRACKER_BUILD_DIR/cargo_target"
 
 # Install system dependecies
 #

tools/devtool

@@ -73,7 +73,7 @@
 # Development container image (name:tag)
 # This should be updated whenever we upgrade the development container.
 # (Yet another step on our way to reproducible builds.)
-DEVCTR_IMAGE="fcuvm/dev:v12"
+DEVCTR_IMAGE="fcuvm/dev:v13"
 
 # Naming things is hard
 MY_NAME="Firecracker $(basename "$0")"