[PATCH v4] rust: query the compiler for dylib path

[Tamir Duberstein <tamird@gmail.com>]

Rust proc-macro crates are loaded by the compiler at compile-time, so
are always dynamic libraries; on macOS, these artifacts get a .dylib
extension rather than .so.

Replace hardcoded paths ending in .so with paths obtained from the
compiler.

This allows the kernel to build with CONFIG_RUST=y on macOS.

Co-developed-by: Fiona Behrens <me@kloenk.dev>
Signed-off-by: Fiona Behrens <me@kloenk.dev>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
V3 -> V4: Added motivation. Added missing Signed-off-by.
V2 -> V3: Added .strip() to rustc output to remove errant newline.
V1 -> V2: De-duplicated and sorted imports. Changed Signed-off-by to
Co-developed-by.

 .gitignore                        |  1 +
 Makefile                          |  2 +-
 rust/Makefile                     | 21 ++++++++++++---------
 scripts/generate_rust_analyzer.py | 15 +++++++++++----
 4 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/.gitignore b/.gitignore
index a61e4778d011..088696a6a46a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -22,6 +22,7 @@
 *.dtb.S
 *.dtbo.S
 *.dwo
+*.dylib
 *.elf
 *.gcno
 *.gcda
diff --git a/Makefile b/Makefile
index a9e723cb0596..470e6f20c513 100644
--- a/Makefile
+++ b/Makefile
@@ -1513,7 +1513,7 @@ MRPROPER_FILES += include/config include/generated          \
 		  certs/x509.genkey \
 		  vmlinux-gdb.py \
 		  rpmbuild \
-		  rust/libmacros.so
+		  rust/libmacros.so rust/libmacros.dylib
 
 # clean - Delete most, but leave enough to build external modules
 #
diff --git a/rust/Makefile b/rust/Makefile
index 0856fd6bc610..94ae550ae8b3 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -11,9 +11,6 @@ always-$(CONFIG_RUST) += exports_core_generated.h
 obj-$(CONFIG_RUST) += helpers/helpers.o
 CFLAGS_REMOVE_helpers/helpers.o = -Wmissing-prototypes -Wmissing-declarations
 
-always-$(CONFIG_RUST) += libmacros.so
-no-clean-files += libmacros.so
-
 always-$(CONFIG_RUST) += bindings/bindings_generated.rs bindings/bindings_helpers_generated.rs
 obj-$(CONFIG_RUST) += alloc.o bindings.o kernel.o
 always-$(CONFIG_RUST) += exports_alloc_generated.h exports_helpers_generated.h \
@@ -36,9 +33,15 @@ always-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.c
 obj-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated.o
 obj-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.o
 
-# Avoids running `$(RUSTC)` for the sysroot when it may not be available.
+# Avoids running `$(RUSTC)` when it may not be available.
 ifdef CONFIG_RUST
 
+libmacros_name := $($(RUSTC) --print file-names --crate-name macros --crate-type proc-macro - < /dev/null)
+libmacros_extension := $(patsubst libmacros.%,%,$(libmacros_name))
+
+always-$(CONFIG_RUST) += $(libmacros_name)
+no-clean-files += $(libmacros_name)
+
 # `$(rust_flags)` is passed in case the user added `--sysroot`.
 rustc_sysroot := $(shell MAKEFLAGS= $(RUSTC) $(rust_flags) --print sysroot)
 rustc_host_target := $(shell $(RUSTC) --version --verbose | grep -F 'host: ' | cut -d' ' -f2)
@@ -118,10 +121,10 @@ rustdoc-alloc: $(RUST_LIB_SRC)/alloc/src/lib.rs rustdoc-core rustdoc-compiler_bu
 	+$(call if_changed,rustdoc)
 
 rustdoc-kernel: private rustc_target_flags = --extern alloc \
-    --extern build_error --extern macros=$(objtree)/$(obj)/libmacros.so \
+    --extern build_error --extern macros=$(objtree)/$(obj)/$(libmacros_name) \
     --extern bindings --extern uapi
 rustdoc-kernel: $(src)/kernel/lib.rs rustdoc-core rustdoc-macros \
-    rustdoc-compiler_builtins rustdoc-alloc $(obj)/libmacros.so \
+    rustdoc-compiler_builtins rustdoc-alloc $(obj)/$(libmacros_name) \
     $(obj)/bindings.o FORCE
 	+$(call if_changed,rustdoc)
 
@@ -342,10 +345,10 @@ quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
 		-Clink-args='$(call escsq,$(KBUILD_HOSTLDFLAGS))' \
 		--emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
 		--crate-type proc-macro \
-		--crate-name $(patsubst lib%.so,%,$(notdir $@)) $<
+		--crate-name $(patsubst lib%.$(libmacros_extension),%,$(notdir $@)) $<
 
 # Procedural macros can only be used with the `rustc` that compiled it.
-$(obj)/libmacros.so: $(src)/macros/lib.rs FORCE
+$(obj)/$(libmacros_name): $(src)/macros/lib.rs FORCE
 	+$(call if_changed_dep,rustc_procmacro)
 
 quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L $@
@@ -424,7 +427,7 @@ $(obj)/uapi.o: $(src)/uapi/lib.rs \
 $(obj)/kernel.o: private rustc_target_flags = --extern alloc \
     --extern build_error --extern macros --extern bindings --extern uapi
 $(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o $(obj)/build_error.o \
-    $(obj)/libmacros.so $(obj)/bindings.o $(obj)/uapi.o FORCE
+    $(obj)/$(libmacros_name) $(obj)/bindings.o $(obj)/uapi.o FORCE
 	+$(call if_changed_rule,rustc_library)
 
 endif # CONFIG_RUST
diff --git a/scripts/generate_rust_analyzer.py b/scripts/generate_rust_analyzer.py
index d2bc63cde8c6..04ff5b25b851 100755
--- a/scripts/generate_rust_analyzer.py
+++ b/scripts/generate_rust_analyzer.py
@@ -8,6 +8,7 @@ import json
 import logging
 import os
 import pathlib
+import subprocess
 import sys
 
 def args_crates_cfgs(cfgs):
@@ -35,8 +36,7 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs):
     crates_cfgs = args_crates_cfgs(cfgs)
 
     def append_crate(display_name, root_module, deps, cfg=[], is_workspace_member=True, is_proc_macro=False):
-        crates_indexes[display_name] = len(crates)
-        crates.append({
+        crate = {
             "display_name": display_name,
             "root_module": str(root_module),
             "is_workspace_member": is_workspace_member,
@@ -47,7 +47,15 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs):
             "env": {
                 "RUST_MODFILE": "This is only for rust-analyzer"
             }
-        })
+        }
+        if is_proc_macro:
+            proc_macro_dylib_name = subprocess.check_output(
+                [os.environ["RUSTC"], "--print", "file-names", "--crate-name", display_name, "--crate-type", "proc-macro", "-"],
+                stdin=subprocess.DEVNULL,
+            ).decode('utf-8').strip()
+            crate["proc_macro_dylib_path"] = f"{objtree}/rust/{proc_macro_dylib_name}"
+        crates_indexes[display_name] = len(crates)
+        crates.append(crate)
 
     # First, the ones in `rust/` since they are a bit special.
     append_crate(
@@ -77,7 +85,6 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs):
         [],
         is_proc_macro=True,
     )
-    crates[-1]["proc_macro_dylib_path"] = f"{objtree}/rust/libmacros.so"
 
     append_crate(
         "build_error",
-- 
2.47.0