tools: Override makefile ARCH variable if defined, but empty

[ Upstream commit 537a2525eaf76ea9b0dca62b994500d8670b39d5 ]

There are a number of tools (bpftool, selftests), that require a
"bootstrap" build. Here, a bootstrap build is a build host variant of
a target. E.g., assume that you're performing a bpftool cross-build on
x86 to riscv, a bootstrap build would then be an x86 variant of
bpftool. The typical way to perform the host build variant, is to pass
"ARCH=" in a sub-make. However, if a variable has been set with a
command argument, then ordinary assignments in the makefile are
ignored.

This side-effect results in that ARCH, and variables depending on ARCH
are not set. Workaround by overriding ARCH to the host arch, if ARCH
is empty.

Fixes: 8859b0da5aac ("tools/bpftool: Fix cross-build")
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Quentin Monnet <qmo@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/bpf/20241127101748.165693-1-bjorn@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/scripts/Makefile.arch b/tools/scripts/Makefile.arch
index b10b7a27c33fd16b10fa3d7fcfd7a5fa372f2d59..de3f2806b8a89d4d0e914f569a32544d1c10097c 100644 (file)
--- a/tools/scripts/Makefile.arch
+++ b/tools/scripts/Makefile.arch
@@ -6,8 +6,8 @@ HOSTARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
                                   -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
                                   -e s/sh[234].*/sh/ -e s/aarch64.*/arm64/ )
 
-ifndef ARCH
-ARCH := $(HOSTARCH)
+ifeq ($(strip $(ARCH)),)
+override ARCH := $(HOSTARCH)
 endif
 
 SRCARCH := $(ARCH)