Merge patch series "`zerocopy` support"

Introduce support for `zerocopy` [1][2]:

    Fast, safe, compile error. Pick two.

    Zerocopy makes zero-cost memory manipulation effortless. We write
    `unsafe` so you don't have to.

It essentially provides derivable traits (e.g. `FromBytes`) and macros
(e.g. `transmute!`) for safely converting between byte sequences and
other types. Having such support allows us to remove some `unsafe` code.

It is among the most downloaded Rust crates (top #50 recent, top #100
all-time downloads; according to crates.io), and it is also used by the
Rust compiler itself.

The series starts with a few preparation commits, then the `zerocopy`
and `zerocopy-derive` crates are added. Finally, an example patch using
it is on top, removing one `unsafe impl`.

I had to adapt the crates slightly (just +2/-3 lines), but both patches
could potentially be provided upstream eventually. Please see the
commits for details.

In total, it is about ~39k lines added, ~32k without counting `benches/`
which are just for documentation purposes.

See the cover letter for `syn` for some more details about depending on
third-party crates in commit 54e3eae85562 ("Merge patch series "`syn`
support"").

The codegen of an isolated example function similar to the patch on top
is essentially identical. It also turns out that (for that particular
case) `zerocopy`'s version, even under `debug-assertions` enabled, has
no remaining panics, unlike a few in the current code (because the
compiler can prove the remaining `ub_checks` statically).

So their "fast, safe" does indeed check out -- at least in that case.

P.S. This version of `zerocopy` has already the unstable `Ptr{,Inner}`
types -- to play with them, please use:

    make ... KRUSTFLAGS=--cfg=zerocopy_unstable_ptr

Link: https://github.com/google/zerocopy [1]
Link: https://docs.rs/zerocopy [2]
Link: https://patch.msgid.link/20260608141439.182634-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

2 files changed, 33 insertions, 6 deletions

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 3498d25b15e8..911745743246 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -329,6 +329,7 @@ rust_common_cmd = \
 	-Zcrate-attr=no_std \
 	-Zcrate-attr='feature($(rust_allowed_features))' \
 	-Zunstable-options --extern pin_init --extern kernel \
+	--extern zerocopy --extern zerocopy_derive \
 	--crate-type rlib -L $(objtree)/rust/ \
 	--sysroot=/dev/null \
 	--out-dir $(dir $@) --emit=dep-info=$(depfile)
diff --git a/scripts/generate_rust_analyzer.py b/scripts/generate_rust_analyzer.py
index d5f9a0ca742c..dc1219736f77 100755
--- a/scripts/generate_rust_analyzer.py
+++ b/scripts/generate_rust_analyzer.py
@@ -26,6 +26,14 @@ def args_crates_cfgs(cfgs: List[str]) -> Dict[str, List[str]]:
 
     return crates_cfgs
 
+def args_crates_envs(envs: List[str]) -> Dict[str, Dict[str, str]]:
+    crates_envs = {}
+    for env in envs:
+        crate, vals = env.split("=", 1)
+        crates_envs[crate] = dict(v.split("=", 1) for v in vals.split())
+
+    return crates_envs
+
 class Dependency(TypedDict):
     crate: int
     name: str
@@ -61,6 +69,7 @@ def generate_crates(
     sysroot_src: pathlib.Path,
     external_src: Optional[pathlib.Path],
     cfgs: List[str],
+    envs: List[str],
     core_edition: str,
 ) -> List[Crate]:
     # Generate the configuration list.
@@ -74,6 +83,7 @@ def generate_crates(
     # Now fill the crates list.
     crates: List[Crate] = []
     crates_cfgs = args_crates_cfgs(cfgs)
+    crates_envs = args_crates_envs(envs)
 
     def get_crate_name(path: pathlib.Path) -> str:
         return invoke_rustc(["--print", "crate-name", str(path)])
@@ -92,6 +102,10 @@ def generate_crates(
             is_workspace_member if is_workspace_member is not None else True
         )
         edition = edition if edition is not None else "2021"
+        crate_env = {
+            "RUST_MODFILE": "This is only for rust-analyzer",
+            **crates_envs.get(display_name, {}),
+        }
         return {
             "display_name": display_name,
             "root_module": str(root_module),
@@ -99,9 +113,7 @@ def generate_crates(
             "deps": deps,
             "cfg": cfg,
             "edition": edition,
-            "env": {
-                "RUST_MODFILE": "This is only for rust-analyzer"
-            }
+            "env": crate_env,
         }
 
     def append_proc_macro_crate(
@@ -240,6 +252,12 @@ def generate_crates(
         [std, proc_macro, proc_macro2, quote, syn],
     )
 
+    zerocopy_derive = append_proc_macro_crate(
+        "zerocopy_derive",
+        srctree / "rust" / "zerocopy-derive" / "lib.rs",
+        [std, proc_macro, proc_macro2, quote, syn],
+    )
+
     build_error = append_crate(
         "build_error",
         srctree / "rust" / "build_error.rs",
@@ -264,6 +282,12 @@ def generate_crates(
         [core, compiler_builtins],
     )
 
+    zerocopy = append_crate(
+        "zerocopy",
+        srctree / "rust" / "zerocopy" / "src" / "lib.rs",
+        [core, compiler_builtins],
+    )
+
     def append_crate_with_generated(
         display_name: str,
         deps: List[Dependency],
@@ -292,7 +316,7 @@ def generate_crates(
     bindings = append_crate_with_generated("bindings", [core, ffi, pin_init])
     uapi = append_crate_with_generated("uapi", [core, ffi, pin_init])
     kernel = append_crate_with_generated(
-        "kernel", [core, macros, build_error, pin_init, ffi, bindings, uapi]
+        "kernel", [core, macros, build_error, pin_init, ffi, bindings, uapi, zerocopy, zerocopy_derive]
     )
 
     scripts = srctree / "scripts"
@@ -337,7 +361,7 @@ def generate_crates(
             append_crate(
                 crate_name,
                 path,
-                [core, kernel, pin_init],
+                [core, kernel, pin_init, zerocopy, zerocopy_derive],
                 cfg=generated_cfg,
             )
 
@@ -347,6 +371,7 @@ def main() -> None:
     parser = argparse.ArgumentParser()
     parser.add_argument('--verbose', '-v', action='store_true')
     parser.add_argument('--cfgs', action='append', default=[])
+    parser.add_argument('--envs', action='append', default=[])
     parser.add_argument("core_edition")
     parser.add_argument("srctree", type=pathlib.Path)
     parser.add_argument("objtree", type=pathlib.Path)
@@ -357,6 +382,7 @@ def main() -> None:
     class Args(argparse.Namespace):
         verbose: bool
         cfgs: List[str]
+        envs: List[str]
         srctree: pathlib.Path
         objtree: pathlib.Path
         sysroot: pathlib.Path
@@ -372,7 +398,7 @@ def main() -> None:
     )
 
     rust_project = {
-        "crates": generate_crates(args.srctree, args.objtree, args.sysroot_src, args.exttree, args.cfgs, args.core_edition),
+        "crates": generate_crates(args.srctree, args.objtree, args.sysroot_src, args.exttree, args.cfgs, args.envs, args.core_edition),
         "sysroot": str(args.sysroot),
     }