[PATCH v3 0/5] tools/build: Allow versioning of all LLVM tools

[PATCH v3 0/5] tools/build: Allow versioning of all LLVM tools

[James Clark]

I ran into the build issue mentioned in the first commit, because using
an option like LLVM=-15 is a documented way to build [1], but only
some of the LLVM tools defined in tools/ support this.

After fixing that, a lot of other tidyups fell out. I didn't go too far,
for example some selftests include tools/testing/selftests/lib.mk which
reimplements some of the LLVM_SUFFIX stuff, but other selftests include
tools/scripts/Makefile.include and I stopped before touching the former.
Some other non build scripts hard code toolchains and I didn't touch
those either, this change is only focused on things that already
include Makefile.include.

[1]: Documentation/kbuild/llvm.rst

Signed-off-by: James Clark <james.clark@linaro.org>
---
Changes in v3:
- Add warning for empty $USE_LD
- Use $HOSTREADELF in bpf Makefile
- Rebase on v7.2-rc3
- Link to v2: https://lore.kernel.org/r/20260518-james-perf-llvm-version-v2-0-f12cc4f031d8@linaro.org

Changes in v2:
- Fix selftests/bpf build. LLD needs to take the full path to be used
  with -fuse-ld=
- Link to v1: https://lore.kernel.org/r/20260514-james-perf-llvm-version-v1-0-6cac1a9a4c8d@linaro.org

---
James Clark (5):
      tools/build: Allow versioning of all LLVM tools defined in Makefile.include
      tools/build: Indent if else blocks
      tools/build: Allow versioning LLVM readelf
      tools/build: selftests: Allow versioning LLVM lld
      tools/build: selftests: Remove some duplicate toolchain definitions

 tools/bpf/resolve_btfids/Makefile    |  3 --
 tools/lib/api/Makefile               |  4 --
 tools/lib/bpf/Makefile               |  8 ++--
 tools/lib/subcmd/Makefile            |  4 --
 tools/lib/symbol/Makefile            |  4 --
 tools/perf/Makefile.perf             |  7 ----
 tools/scripts/Makefile.include       | 79 ++++++++++++++++++++----------------
 tools/testing/selftests/bpf/Makefile | 13 +++---
 8 files changed, 56 insertions(+), 66 deletions(-)
---
base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
change-id: 20260511-james-perf-llvm-version-43ab1cb5bc7d

Best regards,
-- 
James Clark <james.clark@linaro.org>

[PATCH v3 1/5] tools/build: Allow versioning of all LLVM tools defined in Makefile.include

[James Clark]

The version of LLVM tools can be given on the build command with
LLVM=-15, but this isn't applied to all tools. For example $(CC) gets
versioned, but $(CLANG) doesn't. This causes a Perf build with LTO=1 to
fail with an error about mixed clang versions:

 ld.lld: error: libperf/core.o: Unknown attribute kind (86)
   (Producer: 'LLVM18.1.8' Reader: 'LLVM 15.0.7')

This file has two "ifneq ($(LLVM),)" blocks adjacent to each other, so
merge these blocks making it obvious that all tools should be versioned
consistently and there is nothing special about each block.

This also reveals that ?= and "allow-override" are used inconsistently
between the blocks. "allow-override" is technically only required for
builtin variables, but isn't only used on them, and doesn't do any harm
if used on a non-builtin. Make them all "allow-override" for
consistency. The only functional difference this will cause is if there
is a file level definition of one of the variables followed by an
"#include of Makefile.include" which will now overwrite. But this isn't
done and in a later commit some of the duplicate definitions will be
removed for good measure.

There are also some other LLVM tools that are not defined here and will
be moved in a later commit.

Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/scripts/Makefile.include | 37 ++++++++++++++++++++-----------------
 1 file changed, 20 insertions(+), 17 deletions(-)

diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index 41971a68972dda218714d6b95b1d9d92349285c3..7022e78208a236604a681d45b1ff4f2128f412e5 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -61,10 +61,18 @@ $(error Invalid value for LLVM, see Documentation/kbuild/llvm.rst)
 endif
 
 $(call allow-override,CC,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
+$(call allow-override,CLANG,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
+$(call allow-override,HOSTCC,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
 $(call allow-override,AR,$(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX))
+$(call allow-override,HOSTAR,$(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX))
 $(call allow-override,LD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
+$(call allow-override,HOSTLD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
 $(call allow-override,CXX,$(LLVM_PREFIX)clang++$(LLVM_SUFFIX))
 $(call allow-override,STRIP,$(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX))
+$(call allow-override,LLVM_STRIP,$(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX))
+$(call allow-override,LLC,$(LLVM_PREFIX)llc$(LLVM_SUFFIX))
+$(call allow-override,LLVM_CONFIG,$(LLVM_PREFIX)llvm-config$(LLVM_SUFFIX))
+$(call allow-override,LLVM_OBJCOPY,$(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX))
 else
 # Allow setting various cross-compile vars or setting CROSS_COMPILE as a prefix.
 $(call allow-override,CC,$(CROSS_COMPILE)gcc)
@@ -72,26 +80,21 @@ $(call allow-override,AR,$(CROSS_COMPILE)ar)
 $(call allow-override,LD,$(CROSS_COMPILE)ld)
 $(call allow-override,CXX,$(CROSS_COMPILE)g++)
 $(call allow-override,STRIP,$(CROSS_COMPILE)strip)
-endif
-
-CC_NO_CLANG := $(shell $(CC) -dM -E -x c /dev/null | grep -Fq "__clang__"; echo $$?)
 
-ifneq ($(LLVM),)
-HOSTAR  ?= $(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX)
-HOSTCC  ?= $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
-HOSTLD  ?= $(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX)
-else
-HOSTAR  ?= ar
-HOSTCC  ?= gcc
-HOSTLD  ?= ld
+# Host versions aren't prefixed
+$(call allow-override,HOSTAR,ar)
+$(call allow-override,HOSTCC,gcc)
+$(call allow-override,HOSTLD,ld)
+
+# Some tools still require Clang, LLC and/or LLVM utils
+$(call allow-override,CLANG,clang)
+$(call allow-override,LLC,llc)
+$(call allow-override,LLVM_CONFIG,llvm-config)
+$(call allow-override,LLVM_OBJCOPY,llvm-objcopy)
+$(call allow-override,LLVM_STRIP,llvm-strip)
 endif
 
-# Some tools require Clang, LLC and/or LLVM utils
-CLANG		?= clang
-LLC		?= llc
-LLVM_CONFIG	?= llvm-config
-LLVM_OBJCOPY	?= llvm-objcopy
-LLVM_STRIP	?= llvm-strip
+CC_NO_CLANG := $(shell $(CC) -dM -E -x c /dev/null | grep -Fq "__clang__"; echo $$?)
 
 # Some tools require bpftool
 SYSTEM_BPFTOOL	?= bpftool

-- 
2.34.1

[PATCH v3 2/5] tools/build: Indent if else blocks

[James Clark]

These blocks are quite big and unreadable without indentation. Indent
them.

No functional changes intended.

Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/scripts/Makefile.include | 76 +++++++++++++++++++++---------------------
 1 file changed, 38 insertions(+), 38 deletions(-)

diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index 7022e78208a236604a681d45b1ff4f2128f412e5..e81e5b479c563321e458b2a7ad8fca2b4607a254 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -52,46 +52,46 @@ define allow-override
 endef
 
 ifneq ($(LLVM),)
-ifneq ($(filter %/,$(LLVM)),)
-LLVM_PREFIX := $(LLVM)
-else ifneq ($(filter -%,$(LLVM)),)
-LLVM_SUFFIX := $(LLVM)
-else ifneq ($(LLVM),1)
-$(error Invalid value for LLVM, see Documentation/kbuild/llvm.rst)
-endif
+  ifneq ($(filter %/,$(LLVM)),)
+    LLVM_PREFIX := $(LLVM)
+  else ifneq ($(filter -%,$(LLVM)),)
+    LLVM_SUFFIX := $(LLVM)
+  else ifneq ($(LLVM),1)
+    $(error Invalid value for LLVM, see Documentation/kbuild/llvm.rst)
+  endif
 
-$(call allow-override,CC,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
-$(call allow-override,CLANG,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
-$(call allow-override,HOSTCC,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
-$(call allow-override,AR,$(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX))
-$(call allow-override,HOSTAR,$(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX))
-$(call allow-override,LD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
-$(call allow-override,HOSTLD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
-$(call allow-override,CXX,$(LLVM_PREFIX)clang++$(LLVM_SUFFIX))
-$(call allow-override,STRIP,$(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX))
-$(call allow-override,LLVM_STRIP,$(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX))
-$(call allow-override,LLC,$(LLVM_PREFIX)llc$(LLVM_SUFFIX))
-$(call allow-override,LLVM_CONFIG,$(LLVM_PREFIX)llvm-config$(LLVM_SUFFIX))
-$(call allow-override,LLVM_OBJCOPY,$(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX))
+  $(call allow-override,CC,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
+  $(call allow-override,CLANG,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
+  $(call allow-override,HOSTCC,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
+  $(call allow-override,AR,$(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX))
+  $(call allow-override,HOSTAR,$(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX))
+  $(call allow-override,LD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
+  $(call allow-override,HOSTLD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
+  $(call allow-override,CXX,$(LLVM_PREFIX)clang++$(LLVM_SUFFIX))
+  $(call allow-override,STRIP,$(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX))
+  $(call allow-override,LLVM_STRIP,$(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX))
+  $(call allow-override,LLC,$(LLVM_PREFIX)llc$(LLVM_SUFFIX))
+  $(call allow-override,LLVM_CONFIG,$(LLVM_PREFIX)llvm-config$(LLVM_SUFFIX))
+  $(call allow-override,LLVM_OBJCOPY,$(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX))
 else
-# Allow setting various cross-compile vars or setting CROSS_COMPILE as a prefix.
-$(call allow-override,CC,$(CROSS_COMPILE)gcc)
-$(call allow-override,AR,$(CROSS_COMPILE)ar)
-$(call allow-override,LD,$(CROSS_COMPILE)ld)
-$(call allow-override,CXX,$(CROSS_COMPILE)g++)
-$(call allow-override,STRIP,$(CROSS_COMPILE)strip)
-
-# Host versions aren't prefixed
-$(call allow-override,HOSTAR,ar)
-$(call allow-override,HOSTCC,gcc)
-$(call allow-override,HOSTLD,ld)
-
-# Some tools still require Clang, LLC and/or LLVM utils
-$(call allow-override,CLANG,clang)
-$(call allow-override,LLC,llc)
-$(call allow-override,LLVM_CONFIG,llvm-config)
-$(call allow-override,LLVM_OBJCOPY,llvm-objcopy)
-$(call allow-override,LLVM_STRIP,llvm-strip)
+  # Allow setting various cross-compile vars or setting CROSS_COMPILE as a prefix.
+  $(call allow-override,CC,$(CROSS_COMPILE)gcc)
+  $(call allow-override,AR,$(CROSS_COMPILE)ar)
+  $(call allow-override,LD,$(CROSS_COMPILE)ld)
+  $(call allow-override,CXX,$(CROSS_COMPILE)g++)
+  $(call allow-override,STRIP,$(CROSS_COMPILE)strip)
+
+  # Host versions aren't prefixed
+  $(call allow-override,HOSTAR,ar)
+  $(call allow-override,HOSTCC,gcc)
+  $(call allow-override,HOSTLD,ld)
+
+  # Some tools still require Clang, LLC and/or LLVM utils
+  $(call allow-override,CLANG,clang)
+  $(call allow-override,LLC,llc)
+  $(call allow-override,LLVM_CONFIG,llvm-config)
+  $(call allow-override,LLVM_OBJCOPY,llvm-objcopy)
+  $(call allow-override,LLVM_STRIP,llvm-strip)
 endif
 
 CC_NO_CLANG := $(shell $(CC) -dM -E -x c /dev/null | grep -Fq "__clang__"; echo $$?)

-- 
2.34.1

[PATCH v3 3/5] tools/build: Allow versioning LLVM readelf

[James Clark]

Documentation/kbuild/llvm.rst mentions that readelf is included in the
LLVM toolchain, but it's not currently included in this block.

Add it so that LLVM=... options also apply to readelf. Users in tools/
were Perf which was hardcoding it, and another was the BPF makefile.
Both already include Makefile.include so convert them to use the new
variables.

Where readelf wasn't doing anything arch specific, use HOSTREADELF
because it's more likely to be installed.

Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/lib/bpf/Makefile         | 8 ++++----
 tools/perf/Makefile.perf       | 1 -
 tools/scripts/Makefile.include | 4 ++++
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index eca584fb061e16013e76827e4203f6be0477a73e..269fe21fc8da73083367b3c122bdd2b718e12bc5 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -115,12 +115,12 @@ PC_FILE		:= $(addprefix $(OUTPUT),$(PC_FILE))
 
 TAGS_PROG := $(if $(shell which etags 2>/dev/null),etags,ctags)
 
-GLOBAL_SYM_COUNT = $(shell readelf -s --wide $(BPF_IN_SHARED) | \
+GLOBAL_SYM_COUNT = $(shell $(HOSTREADELF) -s --wide $(BPF_IN_SHARED) | \
 			   cut -d "@" -f1 | sed 's/_v[0-9]_[0-9]_[0-9].*//' | \
 			   sed 's/\[.*\]//' | \
 			   awk '/GLOBAL/ && /DEFAULT/ && !/UND|ABS/ {print $$NF}' | \
 			   sort -u | wc -l)
-VERSIONED_SYM_COUNT = $(shell readelf --dyn-syms --wide $(OUTPUT)libbpf.so | \
+VERSIONED_SYM_COUNT = $(shell $(HOSTREADELF) --dyn-syms --wide $(OUTPUT)libbpf.so | \
 			      sed 's/\[.*\]//' | \
 			      awk '/GLOBAL/ && /DEFAULT/ && !/UND|ABS/ {print $$NF}' | \
 			      grep -Eo '[^ ]+@LIBBPF_' | cut -d@ -f1 | sort -u | wc -l)
@@ -183,12 +183,12 @@ check_abi: $(OUTPUT)libbpf.so $(VERSION_SCRIPT)
 		     "versioned symbols in $^ ($(VERSIONED_SYM_COUNT))." \
 		     "Please make sure all LIBBPF_API symbols are"	 \
 		     "versioned in $(VERSION_SCRIPT)." >&2;		 \
-		readelf -s --wide $(BPF_IN_SHARED) |			 \
+		$(HOSTREADELF) -s --wide $(BPF_IN_SHARED) |		 \
 		    cut -d "@" -f1 | sed 's/_v[0-9]_[0-9]_[0-9].*//' |	 \
 		    sed 's/\[.*\]//' |					 \
 		    awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $$NF}'|  \
 		    sort -u > $(OUTPUT)libbpf_global_syms.tmp;		 \
-		readelf --dyn-syms --wide $(OUTPUT)libbpf.so |		 \
+		$(HOSTREADELF) --dyn-syms --wide $(OUTPUT)libbpf.so |	 \
 		    sed 's/\[.*\]//' |					 \
 		    awk '/GLOBAL/ && /DEFAULT/ && !/UND|ABS/ {print $$NF}'|  \
 		    grep -Eo '[^ ]+@LIBBPF_' | cut -d@ -f1 |		 \
diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index 476b8dcaef58cb1f3fa75f46a647c2cfe2352767..4d0d7ae02e06b117487a17691c4e62a138428ac5 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -215,7 +215,6 @@ FLEX    ?= flex
 BISON   ?= bison
 STRIP   = strip
 AWK     = awk
-READELF ?= readelf
 
 # include Makefile.config by default and rule out
 # non-config cases
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index e81e5b479c563321e458b2a7ad8fca2b4607a254..46a3872b87624a7bf475d9b42a3e471f36789dfd 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -73,6 +73,8 @@ ifneq ($(LLVM),)
   $(call allow-override,LLC,$(LLVM_PREFIX)llc$(LLVM_SUFFIX))
   $(call allow-override,LLVM_CONFIG,$(LLVM_PREFIX)llvm-config$(LLVM_SUFFIX))
   $(call allow-override,LLVM_OBJCOPY,$(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX))
+  $(call allow-override,READELF,$(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX))
+  $(call allow-override,HOSTREADELF,$(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX))
 else
   # Allow setting various cross-compile vars or setting CROSS_COMPILE as a prefix.
   $(call allow-override,CC,$(CROSS_COMPILE)gcc)
@@ -80,11 +82,13 @@ else
   $(call allow-override,LD,$(CROSS_COMPILE)ld)
   $(call allow-override,CXX,$(CROSS_COMPILE)g++)
   $(call allow-override,STRIP,$(CROSS_COMPILE)strip)
+  $(call allow-override,READELF,$(CROSS_COMPILE)readelf)
 
   # Host versions aren't prefixed
   $(call allow-override,HOSTAR,ar)
   $(call allow-override,HOSTCC,gcc)
   $(call allow-override,HOSTLD,ld)
+  $(call allow-override,HOSTREADELF,readelf)
 
   # Some tools still require Clang, LLC and/or LLVM utils
   $(call allow-override,CLANG,clang)

-- 
2.34.1

[PATCH v3 4/5] tools/build: selftests: Allow versioning LLVM lld

[James Clark]

Building with LLVM=... could result in a different version of lld being
used than the main toolchain for liburandom_read.so because it's
hardcoded to "lld" in this makefile.

Make it consistent with the rest of the LLVM toolchain by adding an LLD
variable to Makefile.include. Keep the fallback for other architectures
in tools/testing/selftests/bpf/Makefile as it seems like it's something
specific to this make rule and shouldn't be global.

Clang only accepts either a full path to "/x/x/ld.lld" or "lld-15" style
inputs to "-fuse-ld=", so the only way to make it work with both
prefixed and postfixed paths is to always take the full path. Also I
don't think the original use of "lld" over "ld.lld" was significant as
this is always a linux build, so that can be changed to make it work in
both cases.

Add a warning for an empty USE_LD as "shell command -v" can return empty
and GCC won't complain.

Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/scripts/Makefile.include       |  2 ++
 tools/testing/selftests/bpf/Makefile | 12 ++++++++----
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index 46a3872b87624a7bf475d9b42a3e471f36789dfd..92056d3e330eb6596250635b6d932b3b73e7f45f 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -67,6 +67,7 @@ ifneq ($(LLVM),)
   $(call allow-override,HOSTAR,$(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX))
   $(call allow-override,LD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
   $(call allow-override,HOSTLD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
+  $(call allow-override,LLD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
   $(call allow-override,CXX,$(LLVM_PREFIX)clang++$(LLVM_SUFFIX))
   $(call allow-override,STRIP,$(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX))
   $(call allow-override,LLVM_STRIP,$(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX))
@@ -93,6 +94,7 @@ else
   # Some tools still require Clang, LLC and/or LLVM utils
   $(call allow-override,CLANG,clang)
   $(call allow-override,LLC,llc)
+  $(call allow-override,LLD,ld.lld)
   $(call allow-override,LLVM_CONFIG,llvm-config)
   $(call allow-override,LLVM_OBJCOPY,llvm-objcopy)
   $(call allow-override,LLVM_STRIP,llvm-strip)
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index b642ee489ea64046a9b19852780c3a6f009cbd82..d829979861eeabd33272a0d6eca82e7066eabfd7 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -264,30 +264,34 @@ $(OUTPUT)/%:%.c
 
 # LLVM's ld.lld doesn't support all the architectures, so use it only on x86
 ifeq ($(SRCARCH),$(filter $(SRCARCH),x86 riscv))
-LLD := lld
+USE_LD := $(shell command -v $(LLD))
+USE_LD_ERR = linker '$(LLD)' not found - add it to PATH, or pass LLVM=/path/ or LLD=/abs/ld.lld)
 else
-LLD := $(shell command -v $(LD))
+USE_LD := $(shell command -v $(LD))
+USE_LD_ERR = linker '$(LD)' not found - add it to PATH, or pass LLVM=/path/ or LD=/abs/ld)
 endif
 
 # Filter out -static for liburandom_read.so and its dependent targets so that static builds
 # do not fail. Static builds leave urandom_read relying on system-wide shared libraries.
 $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom_read.map
 	$(call msg,LIB,,$@)
+	$(Q)test -n "$(USE_LD)" || { echo "$@: $(USE_LD_ERR)" >&2; exit 1; }
 	$(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
 		     $(filter-out -static,$(COMMON_CFLAGS) $(LDFLAGS)) \
 		     $(filter %.c,$^) $(filter-out -static,$(LDLIBS)) \
 		     -Wno-unused-command-line-argument \
-		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
+		     -fuse-ld=$(USE_LD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
 		     -Wl,--version-script=liburandom_read.map \
 		     -fPIC -shared -o $@
 
 $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_read.so
 	$(call msg,BINARY,,$@)
+	$(Q)test -n "$(USE_LD)" || { echo "$@: $(USE_LD_ERR)" >&2; exit 1; }
 	$(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
 		     $(filter-out -static,$(COMMON_CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
 		     -Wno-unused-command-line-argument \
 		     -lurandom_read $(filter-out -static,$(LDLIBS)) -L$(OUTPUT) \
-		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
+		     -fuse-ld=$(USE_LD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
 		     -Wl,-rpath=. -o $@
 
 $(OUTPUT)/sign-file: ../../../../scripts/sign-file.c

-- 
2.34.1

[PATCH v3 5/5] tools/build: selftests: Remove some duplicate toolchain definitions

[James Clark]

Try to remove some, but not all duplicate toolchain definitions. In
these instances, their makefiles already include
tools/scripts/Makefile.include which defines these in a consistent way.

STRIP is the only one that was set with an '=', but I don't think it
was significant so that difference can be dropped.

Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/bpf/resolve_btfids/Makefile    | 3 ---
 tools/lib/api/Makefile               | 4 ----
 tools/lib/subcmd/Makefile            | 4 ----
 tools/lib/symbol/Makefile            | 4 ----
 tools/perf/Makefile.perf             | 6 ------
 tools/testing/selftests/bpf/Makefile | 1 -
 6 files changed, 22 deletions(-)

diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
index 7672208f65e4bc245c03603634d3aa0093a91096..6fdb6302e0a28e9166175822f42cfbb4f4eb24e5 100644
--- a/tools/bpf/resolve_btfids/Makefile
+++ b/tools/bpf/resolve_btfids/Makefile
@@ -20,9 +20,6 @@ HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)
 		  CROSS_COMPILE="" CLANG_CROSS_FLAGS="" EXTRA_CFLAGS="$(HOSTCFLAGS)"
 
 RM      ?= rm
-HOSTCC  ?= gcc
-HOSTLD  ?= ld
-HOSTAR  ?= ar
 HOSTPKG_CONFIG ?= pkg-config
 CROSS_COMPILE =
 
diff --git a/tools/lib/api/Makefile b/tools/lib/api/Makefile
index 8665c799e0fa7155016e8bc6968ebe76a90e1d13..a228fdb5adba8d7f8282688964a9751a06cb0c79 100644
--- a/tools/lib/api/Makefile
+++ b/tools/lib/api/Makefile
@@ -9,10 +9,6 @@ srctree := $(patsubst %/,%,$(dir $(srctree)))
 #$(info Determined 'srctree' to be $(srctree))
 endif
 
-CC ?= $(CROSS_COMPILE)gcc
-AR ?= $(CROSS_COMPILE)ar
-LD ?= $(CROSS_COMPILE)ld
-
 MAKEFLAGS += --no-print-directory
 
 INSTALL = install
diff --git a/tools/lib/subcmd/Makefile b/tools/lib/subcmd/Makefile
index 8703ab487b68c89406fed575217b57f58e71fb01..9f1ddcf0504d993249991e0af4589db1072465d1 100644
--- a/tools/lib/subcmd/Makefile
+++ b/tools/lib/subcmd/Makefile
@@ -9,10 +9,6 @@ srctree := $(patsubst %/,%,$(dir $(srctree)))
 #$(info Determined 'srctree' to be $(srctree))
 endif
 
-CC ?= $(CROSS_COMPILE)gcc
-LD ?= $(CROSS_COMPILE)ld
-AR ?= $(CROSS_COMPILE)ar
-
 RM = rm -f
 
 MAKEFLAGS += --no-print-directory
diff --git a/tools/lib/symbol/Makefile b/tools/lib/symbol/Makefile
index 426b845edfaccf56f7c246c281a549c18d0f3919..d692abe8add6e243d7b024fe556cc0983eb4b443 100644
--- a/tools/lib/symbol/Makefile
+++ b/tools/lib/symbol/Makefile
@@ -9,10 +9,6 @@ srctree := $(patsubst %/,%,$(dir $(srctree)))
 #$(info Determined 'srctree' to be $(srctree))
 endif
 
-CC ?= $(CROSS_COMPILE)gcc
-AR ?= $(CROSS_COMPILE)ar
-LD ?= $(CROSS_COMPILE)ld
-
 MAKEFLAGS += --no-print-directory
 
 INSTALL = install
diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index 4d0d7ae02e06b117487a17691c4e62a138428ac5..ca67d4b6fc38367c63123332360ccf27102fc086 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -174,11 +174,6 @@ endef
 
 LD += $(EXTRA_LDFLAGS)
 
-HOSTCC  ?= gcc
-HOSTLD  ?= ld
-HOSTAR  ?= ar
-CLANG   ?= clang
-
 # Some distros provide the command $(CROSS_COMPILE)pkg-config for
 # searching packges installed with Multiarch. Use it for cross
 # compilation if it is existed.
@@ -213,7 +208,6 @@ FIND    = find
 INSTALL = install
 FLEX    ?= flex
 BISON   ?= bison
-STRIP   = strip
 AWK     = awk
 
 # include Makefile.config by default and rule out
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index d829979861eeabd33272a0d6eca82e7066eabfd7..49477b03a4607c0c44cf94412d5f75af75c3a766 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -3,7 +3,6 @@ include ../../../build/Build.include
 include ../../../scripts/Makefile.arch
 include ../../../scripts/Makefile.include
 
-CXX ?= $(CROSS_COMPILE)g++
 OBJCOPY ?= $(CROSS_COMPILE)objcopy
 
 CURDIR := $(abspath .)

-- 
2.34.1

Re: [PATCH v3 4/5] tools/build: selftests: Allow versioning LLVM lld

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] Bypassing Clang's internal linker path resolution causes silent linker version mismatches for out-of-path toolchains.
- [Low] Unbalanced parenthesis in the `USE_LD_ERR` error messages.
--

--- Patch [4]: [PATCH v3 4/5] tools/build: selftests: Allow versioning LLVM lld ---
commit cdccb2d14502b0641ebfd4e8ddb945bdb605ed46
Author: James Clark <james.clark@linaro.org>

tools/build: selftests: Allow versioning LLVM lld

This commit updates the BPF selftests Makefile to use the LLD variable
from Makefile.include to ensure consistency with the rest of the LLVM
toolchain. It explicitly resolves paths to the linker via shell commands
and passes the result to clang's -fuse-ld flag.

> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -264,30 +264,34 @@ $(OUTPUT)/%:%.c
>  
>  # LLVM's ld.lld doesn't support all the architectures, so use it only on x86
>  ifeq ($(SRCARCH),$(filter $(SRCARCH),x86 riscv))
> -LLD := lld
> +USE_LD := $(shell command -v $(LLD))

[Severity: Medium]
Will this shell resolution cause silent linker version mismatches if a user
builds with an out-of-path compiler (e.g., CLANG=/path/to/clang) without
setting LLVM= or modifying the system PATH?

Previously, passing -fuse-ld=lld allowed clang to natively resolve the ld.lld
binary relative to its own executable path. Bypassing clang's internal linker
path resolution with `shell command -v` might cause the build to pick up a
system linker (like /usr/bin/ld.lld) instead of the bundled one.

> +USE_LD_ERR = linker '$(LLD)' not found - add it to PATH, or pass LLVM=/path/ or LLD=/abs/ld.lld)

[Severity: Low]
Is there an extra closing parenthesis at the end of this error message string?

>  else
> -LLD := $(shell command -v $(LD))
> +USE_LD := $(shell command -v $(LD))
> +USE_LD_ERR = linker '$(LD)' not found - add it to PATH, or pass LLVM=/path/ or LD=/abs/ld)

[Severity: Low]
Is there also an unbalanced closing parenthesis here?

>  endif

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260715-james-perf-llvm-version-v3-0-8854bfe5af7e@linaro.org?part=4

Re: [PATCH v3 4/5] tools/build: selftests: Allow versioning LLVM lld

[James Clark]

On 15/07/2026 13:45, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> - [Medium] Bypassing Clang's internal linker path resolution causes silent linker version mismatches for out-of-path toolchains.
> - [Low] Unbalanced parenthesis in the `USE_LD_ERR` error messages.
> --
> 
> --- Patch [4]: [PATCH v3 4/5] tools/build: selftests: Allow versioning LLVM lld ---
> commit cdccb2d14502b0641ebfd4e8ddb945bdb605ed46
> Author: James Clark <james.clark@linaro.org>
> 
> tools/build: selftests: Allow versioning LLVM lld
> 
> This commit updates the BPF selftests Makefile to use the LLD variable
> from Makefile.include to ensure consistency with the rest of the LLVM
> toolchain. It explicitly resolves paths to the linker via shell commands
> and passes the result to clang's -fuse-ld flag.
> 
>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
>> --- a/tools/testing/selftests/bpf/Makefile
>> +++ b/tools/testing/selftests/bpf/Makefile
>> @@ -264,30 +264,34 @@ $(OUTPUT)/%:%.c
>>   
>>   # LLVM's ld.lld doesn't support all the architectures, so use it only on x86
>>   ifeq ($(SRCARCH),$(filter $(SRCARCH),x86 riscv))
>> -LLD := lld
>> +USE_LD := $(shell command -v $(LLD))
> 
> [Severity: Medium]
> Will this shell resolution cause silent linker version mismatches if a user
> builds with an out-of-path compiler (e.g., CLANG=/path/to/clang) without
> setting LLVM= or modifying the system PATH?
> 
> Previously, passing -fuse-ld=lld allowed clang to natively resolve the ld.lld
> binary relative to its own executable path. Bypassing clang's internal linker
> path resolution with `shell command -v` might cause the build to pick up a
> system linker (like /usr/bin/ld.lld) instead of the bundled one.
> 

I can just drop this patch. I assumed $LLD should behave like the other 
tools, but it's only used here where the compiler already picks it's 
sibling linker with the correct version.

>> +USE_LD_ERR = linker '$(LLD)' not found - add it to PATH, or pass LLVM=/path/ or LLD=/abs/ld.lld)
> 
> [Severity: Low]
> Is there an extra closing parenthesis at the end of this error message string?
> 
>>   else
>> -LLD := $(shell command -v $(LD))
>> +USE_LD := $(shell command -v $(LD))
>> +USE_LD_ERR = linker '$(LD)' not found - add it to PATH, or pass LLVM=/path/ or LD=/abs/ld)
> 
> [Severity: Low]
> Is there also an unbalanced closing parenthesis here?
> 
>>   endif
>