Re: [PATCH v5] tools build: Fix rust cross compilation

[Ian Rogers]

On Thu, Feb 26, 2026 at 9:00 AM Dmitrii Dolgov <9erthalion6@xxxxxxxxx> wrote:
>
> 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: 2e05bb52a12 ("perf test workload: Add code_with_type test workload")
> Link: https://perfwiki.github.io/main/arm64-cross-compilation-dockerfile/ [1]
> Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>
> Signed-off-by: Dmitrii Dolgov <9erthalion6@xxxxxxxxx>

Not a cross-compilation problem, but is there a way to pass-through
extra flags to the rust compiler? For CFLAGS we have EXTRA_CFLAGS as a
make variable, but I don't see an EXTRA_RUSTFLAGS. I was looking for
this because I was trying to make a build passing "-m32" to CFLAGS to
create a 32-bit perf binary. The link against the rust workload was
failing due to the different object types.

Thanks,
Ian

> ---
> Changes in v5
> - Error out if the target arch is not covered
>
> Changes in v4
> - Fixed incorrect target name for riscv
>
> Changes in v3
> - Improved commit message, add an example of the compilation failure
>
> Changes in v2:
> - Map supported CROSS_COMPILE values to corresponding Rust targets
>
>  tools/build/Build.include  |  9 +++++++++
>  tools/perf/Makefile.config | 18 ++++++++++++++++++
>  tools/perf/Makefile.perf   |  2 +-
>  3 files changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/tools/build/Build.include b/tools/build/Build.include
> index e45b2eb0d24..cd0baa7a168 100644
> --- a/tools/build/Build.include
> +++ b/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
>
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index a8dc72cfe48..15fbba9f4ca 100644
> --- a/tools/perf/Makefile.config
> +++ b/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_$(ARCH))
> +  endif
>  endif
>
>  # Among the variables below, these:
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index 11b63bafdb2..f7b936deeaa 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -274,7 +274,7 @@ ifeq ($(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
>
> base-commit: c5a244bf17caf2de22f9e100832b75f72b31d3e6
> --
> 2.52.0
>