Re: [PATCH bpf-next v2 8/8] selftests/bpf: Avoid static LLVM linking for cross builds

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Flawed native vs cross-build detection using un-normalized `ARCH` against normalized `HOSTARCH`.
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commit 9a32865094dbf702cf09a9de14d120a1f3ca8a92
Author: Leo Yan <leo.yan@arm.com>

selftests/bpf: Avoid static LLVM linking for cross builds

This commit modifies the BPF selftests Makefile to avoid static LLVM linking
during cross builds. It intends to use dynamic linking for cross compilation
while preserving the existing preference for static linking on native builds.

> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 1e47e29ba4214..ffa90674e86f6 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -188,8 +188,15 @@ ifeq ($(feature-llvm),1)
>    LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets
>    # both llvm-config and lib.mk add -D_GNU_SOURCE, which ends up as conflict
>    LLVM_CFLAGS  += $(filter-out -D_GNU_SOURCE,$(shell $(LLVM_CONFIG) --cflags))
> -  # Prefer linking statically if it's available, otherwise fallback to shared
> -  ifeq ($(shell $(LLVM_CONFIG) --link-static --libs >/dev/null 2>&1 && echo static),static)
> +  # Cross compilation must use dynamic linking to avoid unresolved library
> +  # dependencies. For native build, prefer linking statically if it's
> +  # available, otherwise fallback to shared.
> +  ifneq ($(ARCH), $(HOSTARCH))

[Severity: Medium]
Will this comparison accurately identify native builds?

The kernel build system normalizes $(HOSTARCH) (for example, "x86_64" becomes
"x86"), but $(ARCH) might retain the un-normalized string if passed from the
environment or top-level Makefile.

If $(ARCH) is "x86_64" and $(HOSTARCH) is "x86", this check evaluates to true
even on a native build, unintentionally forcing shared LLVM libraries instead
of keeping the static linking behavior as intended.

Would it be more robust to compare $(SRCARCH) to $(HOSTARCH), or to check if
$(CROSS_COMPILE) is empty instead?

> +    LLVM_LINK_STATIC :=
> +  else
> +    LLVM_LINK_STATIC := $(shell $(LLVM_CONFIG) --link-static --libs >/dev/null 2>&1 && echo y)
> +  endif
> +  ifeq ($(LLVM_LINK_STATIC),y)
>      LLVM_LDLIBS  += $(shell $(LLVM_CONFIG) --link-static --libs $(LLVM_CONFIG_LIB_COMPONENTS))

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260602-tools_build_fix_zero_init_bpf_only-v2-0-c76e5250ea1c@arm.com?part=8