[PATCH AUTOSEL 6.6 24/59] tools/build: Fix s390(x) cross-compilation with clang

[PATCH AUTOSEL 6.6 24/59] tools/build: Fix s390(x) cross-compilation with clang

[Sasha Levin]

From: Thomas Weißschuh <thomas.weissschuh@linutronix.de>

[ Upstream commit a40f0cdce78be8a559ee8a85c908049c65a410b2 ]

The heuristic to derive a clang target triple from a GCC one does not work
for s390. GCC uses "s390-linux" while clang expects "s390x-linux" or
"powerz-linux".

Add an explicit override.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Link: https://lore.kernel.org/r/20250620-tools-cross-s390-v2-1-ecda886e00e5@linutronix.de
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Now let me understand better what the issue is. Based on my analysis:

**Backport Status: YES**

This commit fixes a critical cross-compilation issue where the heuristic
to derive a clang target triple from a GCC one fails for s390
architecture. Here's my detailed analysis:

## Analysis of Code Changes:

The patch modifies `tools/scripts/Makefile.include` by adding two lines
after line 104:
```makefile
CLANG_CROSS_FLAGS := --target=$(notdir $(CROSS_COMPILE:%-=%))
+CLANG_TARGET := $(notdir $(CROSS_COMPILE:%-=%))
+CLANG_TARGET := $(subst s390-linux,s390x-linux,$(CLANG_TARGET))
+CLANG_CROSS_FLAGS := --target=$(CLANG_TARGET)
```

## Key Findings:

1. **Bug Type**: This fixes a build failure when cross-compiling kernel
   tools for s390 architecture using clang.

2. **Root Cause**: GCC uses "s390-linux" as the target triple while
   clang expects "s390x-linux" or "systemz-linux". The existing
   heuristic that derives the clang target from the GCC cross-compiler
   prefix fails for s390.

3. **Similar Fixes Already Present**: I found that other parts of the
   kernel already handle this incompatibility:
   - `tools/testing/selftests/nolibc/Makefile:` converts s390-linux to
     systemz-linux
   - `tools/include/nolibc/Makefile:` converts s390-linux to systemz-
     linux
   - `scripts/Makefile.clang:` directly uses s390x-linux-gnu

4. **Impact**: Without this fix, cross-compilation of kernel tools for
   s390 using clang will fail, affecting:
   - Developers building tools for s390 systems
   - CI/CD pipelines that cross-compile for multiple architectures
   - Distribution builders who need to build kernel tools

5. **Risk Assessment**:
   - The change is minimal and isolated to the build system
   - It only affects the clang target selection logic
   - No runtime behavior changes
   - Similar transformations are already proven in other makefiles

6. **Stable Tree Criteria**:
   - ✓ Fixes a real bug that affects users (build failure)
   - ✓ Small and contained fix (2 lines)
   - ✓ No side effects beyond fixing the issue
   - ✓ No architectural changes
   - ✓ Only touches build infrastructure
   - ✓ Minimal risk of regression

This is a clear candidate for stable backporting as it fixes a concrete
build failure with minimal risk.

 tools/scripts/Makefile.include | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index ff527ac065cf..c006e72b4f43 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -98,7 +98,9 @@ else ifneq ($(CROSS_COMPILE),)
 # Allow userspace to override CLANG_CROSS_FLAGS to specify their own
 # sysroots and flags or to avoid the GCC call in pure Clang builds.
 ifeq ($(CLANG_CROSS_FLAGS),)
-CLANG_CROSS_FLAGS := --target=$(notdir $(CROSS_COMPILE:%-=%))
+CLANG_TARGET := $(notdir $(CROSS_COMPILE:%-=%))
+CLANG_TARGET := $(subst s390-linux,s390x-linux,$(CLANG_TARGET))
+CLANG_CROSS_FLAGS := --target=$(CLANG_TARGET)
 GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)gcc 2>/dev/null))
 ifneq ($(GCC_TOOLCHAIN_DIR),)
 CLANG_CROSS_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
-- 
2.39.5