1. 29 Feb, 2024 2 commits
    • Miguel Ojeda's avatar
      rust: upgrade to Rust 1.76.0 · 768409cf
      Miguel Ojeda authored
      This is the next upgrade to the Rust toolchain, from 1.75.0 to 1.76.0
      (i.e. the latest) [1].
      
      See the upgrade policy [2] and the comments on the first upgrade in
      commit 3ed03f4d ("rust: upgrade to Rust 1.68.2").
      
      # Unstable features
      
      No unstable features that we use were stabilized in Rust 1.76.0.
      
      The only unstable features allowed to be used outside the `kernel` crate
      are still `new_uninit,offset_of`, though other code to be upstreamed
      may increase the list.
      
      Please see [3] for details.
      
      # Required changes
      
      `rustc` (and others) now warns when it cannot connect to the Make
      jobserver, thus mark those invocations as recursive as needed. Please
      see the previous commit for details.
      
      # Other changes
      
      Rust 1.76.0 does not emit the `.debug_pub{names,types}` sections anymore
      for DWARFv4 [4][5]. For instance, in the uncompressed debug info case,
      this debug information took:
      
          samples/rust/rust_minimal.o   ~64 KiB (~18% of total object size)
          rust/kernel.o                 ~92 KiB (~15%)
          rust/core.o                  ~114 KiB ( ~5%)
      
      In the compressed debug info (zlib) case:
      
          samples/rust/rust_minimal.o   ~11 KiB (~6%)
          rust/kernel.o                 ~17 KiB (~5%)
          rust/core.o                   ~21 KiB (~1.5%)
      
      In addition, the `rustc_codegen_gcc` backend now does not emit the
      `.eh_frame` section when compiling under `-Cpanic=abort` [6], thus
      removing the need for the patch in the CI to compile the kernel [7].
      Moreover, it also now emits the `.comment` section too [6].
      
      # `alloc` upgrade and reviewing
      
      The vast majority of changes are due to our `alloc` fork being upgraded
      at once.
      
      There are two kinds of changes to be aware of: the ones coming from
      upstream, which we should follow as closely as possible, and the updates
      needed in our added fallible APIs to keep them matching the newer
      infallible APIs coming from upstream.
      
      Instead of taking a look at the diff of this patch, an alternative
      approach is reviewing a diff of the changes between upstream `alloc` and
      the kernel's. This allows to easily inspect the kernel additions only,
      especially to check if the fallible methods we already have still match
      the infallible ones in the new version coming from upstream.
      
      Another approach is reviewing the changes introduced in the additions in
      the kernel fork between the two versions. This is useful to spot
      potentially unintended changes to our additions.
      
      To apply these approaches, one may follow steps similar to the following
      to generate a pair of patches that show the differences between upstream
      Rust and the kernel (for the subset of `alloc` we use) before and after
      applying this patch:
      
          # Get the difference with respect to the old version.
          git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
          git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
              cut -d/ -f3- |
              grep -Fv README.md |
              xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
          git -C linux diff --patch-with-stat --summary -R > old.patch
          git -C linux restore rust/alloc
      
          # Apply this patch.
          git -C linux am rust-upgrade.patch
      
          # Get the difference with respect to the new version.
          git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
          git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
              cut -d/ -f3- |
              grep -Fv README.md |
              xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
          git -C linux diff --patch-with-stat --summary -R > new.patch
          git -C linux restore rust/alloc
      
      Now one may check the `new.patch` to take a look at the additions (first
      approach) or at the difference between those two patches (second
      approach). For the latter, a side-by-side tool is recommended.
      
      Link: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1760-2024-02-08 [1]
      Link: https://rust-for-linux.com/rust-version-policy [2]
      Link: https://github.com/Rust-for-Linux/linux/issues/2 [3]
      Link: https://github.com/rust-lang/compiler-team/issues/688 [4]
      Link: https://github.com/rust-lang/rust/pull/117962 [5]
      Link: https://github.com/rust-lang/rust/pull/118068 [6]
      Link: https://github.com/Rust-for-Linux/ci-rustc_codegen_gcc [7]
      Tested-by: default avatarBoqun Feng <boqun.feng@gmail.com>
      Reviewed-by: default avatarAlice Ryhl <aliceryhl@google.com>
      Link: https://lore.kernel.org/r/20240217002638.57373-2-ojeda@kernel.orgSigned-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
      768409cf
    • Miguel Ojeda's avatar
      kbuild: mark `rustc` (and others) invocations as recursive · ecab4115
      Miguel Ojeda authored
      `rustc` (like Cargo) may take advantage of the jobserver at any time
      (e.g. for backend parallelism, or eventually frontend too). In the kernel,
      we call `rustc` with `-Ccodegen-units=1` (and `-Zthreads` is 1 so far),
      so we do not expect parallelism. However, in the upcoming Rust 1.76.0, a
      warning is emitted by `rustc` [1] when it cannot connect to the jobserver
      it was passed (in many cases, but not all: compiling and `--print sysroot`
      do, but `--version` does not). And given GNU Make always passes
      the jobserver in the environment variable (even when a line is deemed
      non-recursive), `rustc` will end up complaining about it (in particular
      in Make 4.3 where there is only the simple pipe jobserver style).
      
      One solution is to remove the jobserver from `MAKEFLAGS`. However, we
      can mark the lines with calls to `rustc` (and Cargo) as recursive, which
      looks simpler. This is being documented as a recommendation in `rustc`
      [2] and allows us to be ready for the time we may use parallelism inside
      `rustc` (potentially now, if a user passes `-Zthreads`). Thus do so.
      
      Similarly, do the same for `rustdoc` and `cargo` calls.
      
      Finally, there is one case that the solution does not cover, which is the
      `$(shell ...)` call we have. Thus, for that one, set an empty `MAKEFLAGS`
      environment variable.
      
      Link: https://github.com/rust-lang/rust/issues/120515 [1]
      Acked-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
      Link: https://github.com/rust-lang/rust/pull/121564 [2]
      Link: https://lore.kernel.org/r/20240217002638.57373-1-ojeda@kernel.org
      [ Reworded to add link to PR documenting the recommendation. ]
      Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
      ecab4115
  2. 25 Feb, 2024 4 commits
  3. 18 Feb, 2024 17 commits
  4. 28 Jan, 2024 4 commits
  5. 22 Jan, 2024 2 commits
  6. 21 Jan, 2024 11 commits