[PATCH] rust: Suppress searching builtin sysroot

[Matthew Maurer]

By default, if Rust is passed `--target=foo` rather than a target.json
file, it will infer a default sysroot if that component is installed. As
the proposed aarch64 support uses `aarch64-unknown-none` rather than a
target.json file, this is needed to prevent rustc from being confused
between the custom kernel sysroot and the pre-installed one.

Signed-off-by: Matthew Maurer <mmaurer@xxxxxxxxxx>
---

This patch is prompted by the issue I encountered at
https://lore.kernel.org/all/CAGSQo01pOixiPXkW867h4vPUaAjtKtHGKhkV-rpifJvKxAf4Ww@xxxxxxxxxxxxxx/
but should be generically more hermetic even if we don't end up landing
that patch.

 rust/Makefile          | 1 +
 scripts/Makefile.build | 1 +
 2 files changed, 2 insertions(+)

diff --git a/rust/Makefile b/rust/Makefile
index a27f35f924ec..0403e88e19fd 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -400,6 +400,7 @@ quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L
 		--emit=metadata=$(dir $@)$(patsubst %.o,lib%.rmeta,$(notdir $@)) \
 		--crate-type rlib -L$(objtree)/$(obj) \
 		--crate-name $(patsubst %.o,%,$(notdir $@)) $< \
+		--sysroot=/dev/null \
 	$(if $(rustc_objcopy),;$(OBJCOPY) $(rustc_objcopy) $@)
 
 rust-analyzer:
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 82e3fb19fdaf..6e4ee513cc3c 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -275,6 +275,7 @@ rust_common_cmd = \
 	--extern alloc --extern kernel \
 	--crate-type rlib -L $(objtree)/rust/ \
 	--crate-name $(basename $(notdir $@)) \
+	--sysroot=/dev/null \
 	--out-dir $(dir $@) --emit=dep-info=$(depfile)
 
 # `--emit=obj`, `--emit=asm` and `--emit=llvm-ir` imply a single codegen unit
-- 
2.42.0.820.g83a721a137-goog