[PATCH] kbuild: host: use single executable for rustc -C linker

[Mohamad Alsadhan]

rustc's -C linker= option expects a single executable path. When
HOSTCC contains a wrapper (e.g. "ccache gcc"), passing
-Clinker=$(HOSTCC) results in the shell splitting the value into
multiple words, and rustc interprets the additional word as an
input filename:

  error: multiple input filenames provided ...

Use the last word of HOSTCC as the linker executable for host
Rust tools. This preserves wrapper usage for C host tools while
ensuring rustc receives a single executable path.

Closes: https://github.com/Rust-for-Linux/linux/issues/1224

Signed-off-by: Mohamad Alsadhan <mo@xxxxxxx>
---
 scripts/Makefile.host | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index c1dedf646..22eab2734 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -87,11 +87,18 @@ hostcxx_flags  = -Wp,-MMD,$(depfile) \
                  $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
                  $(HOSTCXXFLAGS_$(target-stem).o)
 
+# rustc's `-C linker=` expects a single executable path, not a command line.
+# HOSTCC may be a multi-word command when wrapped (e.g. "ccache gcc"),
+# which would otherwise be split by the shell and mis-parsed by rustc.
+#
+# Use a dedicated variable for the linker program used by host Rust tools.
+HOSTRUSTC_LINKER ?= $(lastword $(HOSTCC))
+
 # `--out-dir` is required to avoid temporaries being created by `rustc` in the
 # current working directory, which may be not accessible in the out-of-tree
 # modules case.
 hostrust_flags = --out-dir $(dir $@) --emit=dep-info=$(depfile) \
-		 -Clinker-flavor=gcc -Clinker=$(HOSTCC) \
+		 -Clinker-flavor=gcc -Clinker=$(HOSTRUSTC_LINKER) \
 		 -Clink-args='$(call escsq,$(KBUILD_HOSTLDFLAGS))' \
                  $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
                  $(HOSTRUSTFLAGS_$(target-stem))
-- 
2.52.0