# --- T2-COPYRIGHT-BEGIN ---
# t2/package/*/perf/hotfix-rust-cross.patch
# Copyright (C) 2026 The T2 SDE Project
# SPDX-License-Identifier: GPL-2.0 or patched project license
# --- T2-COPYRIGHT-END ---

Make the perf Rust support cross-compile aware.

The Rust test workload was compiled without a --target, producing host
objects that break the final ld -r merge in cross builds. Derive the Rust
target triple from $(CC) -dumpmachine and pass it via rust_flags, and turn
the rustc feature check into a metadata-only compilation so a missing
target standard library correctly disables the Rust test workloads.

Signed-off-by: René Rebe <rene@exactco.de>

--- a/tools/build/feature/Makefile	2026-02-23 17:31:55.000000000 +0100
+++ b/tools/build/feature/Makefile	2026-08-28 10:49:45.200977920 +0200
@@ -390,13 +390,13 @@ $(OUTPUT)test-bpftool-skeletons.bin:
 	$(SYSTEM_BPFTOOL) version | grep '^features:.*skeletons' \
 		> $(@:.bin=.make.output) 2>&1
 
-# Testing Rust is special: we don't compile anything, it's enough to check the
-# compiler presence. Compiling a test code for this purposes is problematic,
-# because Rust will emit a dependency file without any external references,
-# meaning that if rustc will be removed the build process will still think it's
-# there.
+# Testing Rust needs an actual compilation so a missing standard library for
+# the (possibly cross) target is detected. A metadata-only build verifies the
+# compiler and the target libraries without linking and without emitting a
+# dependency file.
 $(OUTPUT)test-rust.bin:
-	$(RUSTC) --version > /dev/null 2>&1
+	echo 'fn main() {}' | $(RUSTC) $(rust_flags) --crate-type lib \
+		--emit=metadata=$@ - > /dev/null 2>&1
 
 ###############################
 
--- a/tools/perf/Makefile.config	2026-02-23 17:31:55.000000000 +0100
+++ b/tools/perf/Makefile.config	2026-08-28 10:51:02.766202780 +0200
@@ -1154,6 +1154,18 @@ ifneq ($(NO_LIBTRACEEVENT),1)
 endif
 
 ifndef NO_RUST
+  # For cross builds pass a matching --target to rustc, falling back to a
+  # vendor-neutral triple if rustc does not know the toolchain vendor.
+  CC_TARGET := $(shell $(CC) -dumpmachine 2>/dev/null)
+  RUSTC_HOST := $(shell $(RUSTC) -vV 2>/dev/null | sed -n 's/^host: //p')
+  ifneq ($(CC_TARGET),$(RUSTC_HOST))
+    RUST_TARGET ?= $(CC_TARGET)
+    ifeq ($(findstring $(RUST_TARGET),$(shell $(RUSTC) --print target-list 2>/dev/null)),)
+      RUST_TARGET := $(shell echo $(RUST_TARGET) | sed -E 's/^([^-]+)-[^-]+-(linux-.*)/\1-unknown-\2/')
+    endif
+    rust_flags += --target=$(RUST_TARGET)
+    export rust_flags
+  endif
   $(call feature_check,rust)
   ifneq ($(feature-rust), 1)
     $(warning Rust is not found. Test workloads with rust are disabled.)