[PATCH] tools: Override makefile ARCH variable if defined, but empty

["Björn Töpel" <bjorn@kernel.org>]

From: Björn Töpel <bjorn@rivosinc.com>

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>
---
 tools/scripts/Makefile.arch | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/scripts/Makefile.arch b/tools/scripts/Makefile.arch
index f6a50f06dfc4..eabfe9f411d9 100644
--- a/tools/scripts/Makefile.arch
+++ b/tools/scripts/Makefile.arch
@@ -7,8 +7,8 @@ HOSTARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
                                   -e s/sh[234].*/sh/ -e s/aarch64.*/arm64/ \
                                   -e s/riscv.*/riscv/ -e s/loongarch.*/loongarch/)
 
-ifndef ARCH
-ARCH := $(HOSTARCH)
+ifeq ($(strip $(ARCH)),)
+override ARCH := $(HOSTARCH)
 endif
 
 SRCARCH := $(ARCH)

base-commit: 7758b206117dab9894f0bcb8333f8e4731c5065a
-- 
2.45.2