tools build: Fix rust cross compilation

Currently no target is specified to compile rust code when needed, which
breaks cross compilation. E.g. for arm64:

      LD      /tmp/build/tests/workloads/perf-test-in.o
    aarch64-linux-gnu-ld: /tmp/build/tests/workloads/code_with_type.a(code_with_type.code_with_type.d12f4324cb53c560-cgu.0.rcgu.o): Relocations in generic ELF (EM: 62)
    aarch64-linux-gnu-ld: /tmp/build/tests/workloads/code_with_type.a(code_with_type.code_with_type.d12f4324cb53c560-cgu.0.rcgu.o): Relocations in generic ELF (EM: 62)
    [...repeated...]
    aarch64-linux-gnu-ld: /tmp/build/tests/workloads/code_with_type.a(code_with_type.code_with_type.d12f4324cb53c560-cgu.0.rcgu.o): Relocations in generic ELF (EM: 62)
    aarch64-linux-gnu-ld: /tmp/build/tests/workloads/code_with_type.a(code_with_type.code_with_type.d12f4324cb53c560-cgu.0.rcgu.o): Relocations in generic ELF (EM: 62)
    aarch64-linux-gnu-ld: /tmp/build/tests/workloads/code_with_type.a: error adding symbols: file in wrong format
    make[5]: *** [/perf/tools/build/Makefile.build:162: /tmp/build/tests/workloads/perf-test-in.o] Error 1
    make[4]: *** [/perf/tools/build/Makefile.build:156: workloads] Error 2
    make[3]: *** [/perf/tools/build/Makefile.build:156: tests] Error 2
    make[2]: *** [Makefile.perf:785: /tmp/build/perf-test-in.o] Error 2
    make[2]: *** Waiting for unfinished jobs....
    make[1]: *** [Makefile.perf:289: sub-make] Error 2
    make: *** [Makefile:76: all] Error 2

Detect required target and pass it via rust_flags to the compiler.

Note that CROSS_COMPILE might be different from what rust compiler
expects, since it may omit the target vendor value, e.g.
"aarch64-linux-gnu" instead of "aarch64-unknown-linux-gnu".

Thus explicitly map supported CROSS_COMPILE values to corresponding Rust
versions, as suggested by Miguel Ojeda.

Tested using arm64 cross-compilation example from [1].

Fixes: 2e05bb5 ("perf test workload: Add code_with_type test workload")
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com>
Cc: Levi Zim <i@kxxt.dev>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nsc@kernel.org>
Link: https://perfwiki.github.io/main/arm64-cross-compilation-dockerfile/ [1]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: erthalion

tools/build/Build.include

@@ -98,6 +98,15 @@ c_flags_2 = $(filter-out $(CFLAGS_REMOVE_$(basetarget).o), $(c_flags_1))
 c_flags   = $(filter-out $(CFLAGS_REMOVE_$(obj)), $(c_flags_2))
 cxx_flags = -Wp,-MD,$(depfile) -Wp,-MT,$@ $(CXXFLAGS) -D"BUILD_STR(s)=\#s" $(CXXFLAGS_$(basetarget).o) $(CXXFLAGS_$(obj))
 
+###
+# Rust flags to be used on rule definition, includes:
+# - global $(RUST_FLAGS)
+# - per target Rust flags
+# - per object Rust flags
+rust_flags_1 = $(RUST_FLAGS) $(RUST_FLAGS_$(basetarget).o) $(RUST_FLAGS_$(obj))
+rust_flags_2 = $(filter-out $(RUST_FLAGS_REMOVE_$(basetarget).o), $(rust_flags_1))
+rust_flags   = $(filter-out $(RUST_FLAGS_REMOVE_$(obj)), $(rust_flags_2))
+
 ###
 ## HOSTCC C flags
 

tools/perf/Makefile.config

@@ -1163,6 +1163,24 @@ ifndef NO_RUST
     CFLAGS += -DHAVE_RUST_SUPPORT
     $(call detected,CONFIG_RUST_SUPPORT)
   endif
+
+  ifneq ($(CROSS_COMPILE),)
+    RUST_TARGET_FLAGS_arm	:= arm-unknown-linux-gnueabi
+    RUST_TARGET_FLAGS_arm64	:= aarch64-unknown-linux-gnu
+    RUST_TARGET_FLAGS_m68k	:= m68k-unknown-linux-gnu
+    RUST_TARGET_FLAGS_mips	:= mipsel-unknown-linux-gnu
+    RUST_TARGET_FLAGS_powerpc	:= powerpc64le-unknown-linux-gnu
+    RUST_TARGET_FLAGS_riscv	:= riscv64gc-unknown-linux-gnu
+    RUST_TARGET_FLAGS_s390	:= s390x-unknown-linux-gnu
+    RUST_TARGET_FLAGS_x86	:= x86_64-unknown-linux-gnu
+    RUST_TARGET_FLAGS_x86_64	:= x86_64-unknown-linux-gnu
+
+    ifeq ($(RUST_TARGET_FLAGS_$(ARCH)),)
+      $(error Unknown rust cross compilation architecture $(ARCH))
+    endif
+
+    RUST_FLAGS += --target=$(RUST_TARGET_FLAGS_$(ARCH))
+  endif
 endif
 
 # Among the variables below, these:

tools/perf/Makefile.perf

@@ -274,7 +274,7 @@ ifeq ($(PYLINT),1)
   PYLINT := $(shell which pylint 2> /dev/null)
 endif
 
-export srctree OUTPUT RM CC CXX RUSTC LD AR CFLAGS CXXFLAGS V BISON FLEX AWK
+export srctree OUTPUT RM CC CXX RUSTC LD AR CFLAGS CXXFLAGS RUST_FLAGS V BISON FLEX AWK
 export HOSTCC HOSTLD HOSTAR HOSTCFLAGS SHELLCHECK MYPY PYLINT
 
 include $(srctree)/tools/build/Makefile.include