Re: [PATCH v3 1/2] perf build: Support building BPF skeletons with bpf-gcc

[Namhyung Kim <namhyung@kernel.org>]

On Thu, Oct 22, 2026 at 01:46:26PM -0700, Ian Rogers wrote:
> Support building perf BPF skeletons with bpf-gcc (>= 14.0.0) in addition
> to clang (>= 12.0.1), similar to tools/testing/selftests/bpf/Makefile.
> 
> When building perf with GCC (CC_NO_CLANG=1), prefer bpf-gcc and fall
> back to clang if bpf-gcc is unavailable or too old. When building with
> Clang/LLVM (CC_NO_CLANG=0), prefer clang and fall back to bpf-gcc.
> Explicit command-line overrides via BPF_GCC=... or CLANG=... are
> respected, and setting BPF_GCC= or CLANG= to empty disables that
> compiler.
> 
> In bpf_skel.mak, pass the bpf-gcc flags (-mcpu=v3, -fno-ident,
> -DBPF_NO_PRESERVE_ACCESS_INDEX, -Wno-attributes,
> -D__TARGET_ARCH_$(SRCARCH), and target endianness) and query system
> include paths from $(CC).
> 
> Also update version-ge3 and version-lt3 in tools/scripts/utilities.mak
> to split the two version arguments separately in awk so empty or
> fewer-than-3-component version strings do not shift fields across
> arguments.

Sorry for the delay.  But can you please split this part from the
bpf-gcc changes?

Thanks,
Namhyung

> 
> Assisted-by: Antigravity:gemini-3.1-pro
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/Makefile.config     | 83 +++++++++++++++++++++++++++-------
>  tools/perf/Makefile.perf       |  8 +++-
>  tools/perf/bpf_skel.mak        | 36 ++++++++++-----
>  tools/scripts/Makefile.include |  1 +
>  tools/scripts/utilities.mak    |  4 +-
>  5 files changed, 101 insertions(+), 31 deletions(-)
> 
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index cafc7be79643..ca045f7ff01d 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -662,27 +662,78 @@ ifeq ($(BUILD_BPF_SKEL),1)
>    else ifeq ($(filter -DHAVE_LIBOPENSSL_SUPPORT, $(CFLAGS)),)
>      $(warning Warning: Disabled BPF skeletons as libopenssl is required)
>      BUILD_BPF_SKEL := 0
> -  else ifeq ($(call get-executable,$(CLANG)),)
> -    $(warning Warning: Disabled BPF skeletons as clang ($(CLANG)) is missing)
> -    BUILD_BPF_SKEL := 0
> -  else
> -    CLANG_VERSION := $(shell $(CLANG) --version | head -1 | sed 's/.*clang version \([[:digit:]]\+.[[:digit:]]\+.[[:digit:]]\+\).*/\1/g')
> -    ifeq ($(call version-lt3,$(CLANG_VERSION),12.0.1),1)
> -      $(warning Warning: Disabled BPF skeletons as reliable BTF generation needs at least $(CLANG) version 12.0.1)
> -      BUILD_BPF_SKEL := 0
> -    endif
>    endif
>    ifeq ($(BUILD_BPF_SKEL),1)
> -    $(call feature_check,clang-bpf-co-re)
> -    ifeq ($(feature-clang-bpf-co-re), 0)
> -      $(warning Warning: Disabled BPF skeletons as clang is too old)
> +    # Prefer bpf-gcc when building with gcc (CC_NO_CLANG=1) and clang when
> +    # building with clang, unless CLANG or BPF_GCC was explicitly specified on
> +    # the command line. Fall back to whichever compiler is available.
> +    prefer_bpf_gcc := $(CC_NO_CLANG)
> +    ifeq ($(origin BPF_GCC),command line)
> +      ifneq ($(BPF_GCC),)
> +        prefer_bpf_gcc := 1
> +      endif
> +    else ifeq ($(origin CLANG),command line)
> +      ifneq ($(CLANG),)
> +        prefer_bpf_gcc := 0
> +      endif
> +    endif
> +
> +    have_bpf_gcc := 0
> +    have_clang_bpf := 0
> +
> +    define check_bpf_gcc
> +      ifneq ($$(call get-executable,$$(BPF_GCC)),)
> +        BPF_GCC_VERSION := $$(shell $$(BPF_GCC) -dumpfullversion 2>/dev/null)
> +        ifneq ($$(BPF_GCC_VERSION),)
> +          ifneq ($$(call version-lt3,$$(BPF_GCC_VERSION),14.0.0),1)
> +            have_bpf_gcc := 1
> +          endif
> +        endif
> +      endif
> +    endef
> +
> +    ifeq ($(prefer_bpf_gcc),1)
> +      $(eval $(check_bpf_gcc))
> +    endif
> +
> +    ifeq ($(have_bpf_gcc),0)
> +      ifneq ($(call get-executable,$(CLANG)),)
> +        CLANG_VERSION := $(shell $(CLANG) --version | head -1 | sed 's/.*clang version \([[:digit:]]\+.[[:digit:]]\+.[[:digit:]]\+\).*/\1/g')
> +        ifneq ($(call version-lt3,$(CLANG_VERSION),12.0.1),1)
> +          $(call feature_check,clang-bpf-co-re)
> +          ifneq ($(feature-clang-bpf-co-re), 0)
> +            have_clang_bpf := 1
> +          endif
> +        endif
> +      endif
> +    endif
> +
> +    ifeq ($(prefer_bpf_gcc)$(have_clang_bpf),00)
> +      $(eval $(check_bpf_gcc))
> +    endif
> +
> +    ifeq ($(have_bpf_gcc),1)
> +      $(call detected,CONFIG_PERF_BPF_SKEL_BPF_GCC)
> +      $(call detected,CONFIG_PERF_BPF_SKEL)
> +      CFLAGS += -DHAVE_BPF_SKEL
> +    else ifeq ($(have_clang_bpf),1)
> +      $(call detected,CONFIG_PERF_BPF_SKEL)
> +      CFLAGS += -DHAVE_BPF_SKEL
> +    else
> +      ifeq ($(call get-executable,$(CLANG))$(call get-executable,$(BPF_GCC)),)
> +        $(warning Warning: Disabled BPF skeletons as clang ($(CLANG)) and bpf-gcc ($(BPF_GCC)) are missing)
> +      else ifneq ($(call get-executable,$(CLANG)),)
> +        ifeq ($(call version-lt3,$(CLANG_VERSION),12.0.1),1)
> +          $(warning Warning: Disabled BPF skeletons as reliable BTF generation needs at least $(CLANG) version 12.0.1)
> +        else
> +          $(warning Warning: Disabled BPF skeletons as clang is too old)
> +        endif
> +      else
> +        $(warning Warning: Disabled BPF skeletons as bpf-gcc ($(BPF_GCC)) needs at least version 14.0.0)
> +      endif
>        BUILD_BPF_SKEL := 0
>      endif
>    endif
> -  ifeq ($(BUILD_BPF_SKEL),1)
> -    $(call detected,CONFIG_PERF_BPF_SKEL)
> -    CFLAGS += -DHAVE_BPF_SKEL
> -  endif
>  endif
>  
>  ifndef GEN_VMLINUX_H
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index 2d9379fea267..4061a79cae54 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -37,6 +37,9 @@ include ../scripts/utilities.mak
>  # Define EXTRA_BPF_FLAGS="--sysroot=<path>" or other custom include paths for
>  # cross-compiling BPF skeletons
>  #
> +# Define BPF_GCC to point to the bpf-gcc binary if the default `bpf-gcc' is not
> +# correct, or set BPF_GCC= to disable using bpf-gcc for BPF skeletons.
> +#
>  # Define EXCLUDE_EXTLIBS=-lmylib to exclude libmylib from the auto-generated
>  # EXTLIBS.
>  #
> @@ -208,6 +211,7 @@ FIND    = find
>  INSTALL = install
>  FLEX    ?= flex
>  BISON   ?= bison
> +BPF_GCC ?= bpf-gcc
>  AWK     = awk
>  
>  # include Makefile.config by default and rule out
> @@ -321,8 +325,8 @@ ifneq ($(force_fixdep),1)
>    endif
>  endif
>  
> -export srctree OUTPUT RM CC CXX RUSTC CLANG LD AR CFLAGS CXXFLAGS RUST_FLAGS V BISON FLEX AWK LIBBPF READELF
> -export HOSTCC HOSTLD HOSTAR HOSTCFLAGS SHELLCHECK MYPY PYLINT CONFIG_PERF_BPF_SKEL
> +export srctree OUTPUT RM CC CXX RUSTC CLANG BPF_GCC LD AR CFLAGS CXXFLAGS RUST_FLAGS V BISON FLEX AWK LIBBPF READELF
> +export HOSTCC HOSTLD HOSTAR HOSTCFLAGS SHELLCHECK MYPY PYLINT CONFIG_PERF_BPF_SKEL CONFIG_PERF_BPF_SKEL_BPF_GCC
>  
>  include $(srctree)/tools/build/Makefile.include
>  
> diff --git a/tools/perf/bpf_skel.mak b/tools/perf/bpf_skel.mak
> index f2559de39f96..7b7edf506509 100644
> --- a/tools/perf/bpf_skel.mak
> +++ b/tools/perf/bpf_skel.mak
> @@ -22,21 +22,35 @@ bpf-skel-prepare: $(BPFTOOL) $(VMLINUX_H)
>  define get_sys_includes
>  $(shell $(1) $(2) -v -E - </dev/null 2>&1 \
>         | sed -n '/<...> search starts here:/,/End of search list./{ s| \(/.*\)|-idirafter \1|p }') \
> -$(shell $(1) $(2) -dM -E - </dev/null | grep '__riscv_xlen ' | awk '{printf("-D__riscv_xlen=%d -D__BITS_PER_LONG=%d", $$3, $$3)}')
> +$(shell $(1) $(2) -dM -E - </dev/null | grep '__riscv_xlen ' | awk '{printf("-D__riscv_xlen=%d -D__BITS_PER_LONG=%d", $$3, $$3)}') \
> +$(shell $(1) $(2) -dM -E - </dev/null | grep '__loongarch_grlen ' | awk '{printf("-D__BITS_PER_LONG=%d", $$3)}') \
> +$(shell $(1) $(2) -dM -E - </dev/null | grep -E 'MIPS(EL|EB)|_MIPS_SZ(PTR|LONG) |_MIPS_SIM |_ABI(O32|N32|64) ' | awk '{printf("-D%s=%s ", $$2, $$3)}')
>  endef
>  
> -ifneq ($(CROSS_COMPILE),)
> -CLANG_TARGET_ARCH = --target=$(notdir $(CROSS_COMPILE:%-=%))
> +ifeq ($(CONFIG_PERF_BPF_SKEL_BPF_GCC),y)
> +  BPF_CC := $(BPF_GCC)
> +  QUIET_BPF_CC = $(QUIET_BPF_GCC)
> +  IS_LITTLE_ENDIAN := $(shell $(CC) -dM -E - </dev/null | \
> +			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
> +  BPF_OPTIONS = -Wall -mcpu=v3 -fno-ident -DBPF_NO_PRESERVE_ACCESS_INDEX -Wno-attributes \
> +		-D__TARGET_ARCH_$(SRCARCH) $(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
> +  BPF_SYS_INCLUDES = $(call get_sys_includes,$(CC),)
> +else
> +  BPF_CC := $(CLANG)
> +  QUIET_BPF_CC = $(QUIET_CLANG)
> +  ifneq ($(CROSS_COMPILE),)
> +    CLANG_TARGET_ARCH = --target=$(notdir $(CROSS_COMPILE:%-=%))
> +  endif
> +  BPF_OPTIONS = -Wall -mcpu=v3 -fno-stack-protector --target=bpf -Wno-microsoft-anon-tag
> +  BPF_SYS_INCLUDES = $(call get_sys_includes,$(CLANG),$(CLANG_TARGET_ARCH))
>  endif
>  
> -CLANG_OPTIONS = -Wall -mcpu=v3
> -CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG),$(CLANG_TARGET_ARCH))
>  LIBBPF_INCLUDE := $(abspath $(or $(OUTPUT),.))/libbpf/include
> -BPF_INCLUDE := -I$(SKEL_TMP_OUT)/.. -I$(SKEL_TOOL_OUT) -I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES)
> +BPF_INCLUDE := -I$(SKEL_TMP_OUT)/.. -I$(SKEL_TOOL_OUT) -I$(LIBBPF_INCLUDE) $(BPF_SYS_INCLUDES)
>  TOOLS_UAPI_INCLUDE := -I$(srctree)/tools/include/uapi
>  
>  ifneq ($(WERROR),0)
> -  CLANG_OPTIONS += -Werror
> +  BPF_OPTIONS += -Werror
>  endif
>  
>  $(BPFTOOL):
> @@ -83,11 +97,11 @@ endif
>  # Consolidated Pattern rule for $(dir)/bpf_skel/
>  $(SKEL_TMP_OUT)/%.bpf.o: $(srctree)/tools/perf/$(dir)/bpf_skel/%.bpf.c $(LIBBPF) $(VMLINUX_H) $(OUTPUT)PERF-VERSION-FILE util/bpf_skel/perf_version.h
>  	$(call rule_mkdir)
> -	$(QUIET_CLANG)
> -	$(Q)$(CLANG) -g -O2 -fno-stack-protector --target=bpf \
> -	  $(CLANG_OPTIONS) $(EXTRA_BPF_FLAGS) $(BPF_INCLUDE) $(TOOLS_UAPI_INCLUDE) \
> +	$(QUIET_BPF_CC)
> +	$(Q)$(BPF_CC) -g -O2 \
> +	  $(BPF_OPTIONS) $(EXTRA_BPF_FLAGS) $(BPF_INCLUDE) $(TOOLS_UAPI_INCLUDE) \
>  	  -include $(OUTPUT)PERF-VERSION-FILE -include util/bpf_skel/perf_version.h \
> -	  -fms-extensions -Wno-microsoft-anon-tag \
> +	  -fms-extensions \
>  	  -c $< -o $@
>  
>  $(SKEL_OUT)/%.skel.h: $(SKEL_TMP_OUT)/%.bpf.o $(BPFTOOL)
> diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
> index 378387f62960..9967210b2928 100644
> --- a/tools/scripts/Makefile.include
> +++ b/tools/scripts/Makefile.include
> @@ -217,6 +217,7 @@ ifneq ($(silent),1)
>  	QUIET_CC       = @echo '  CC      '$@;
>  	QUIET_CC_FPIC  = @echo '  CC FPIC '$@;
>  	QUIET_CLANG    = @echo '  CLANG   '$@;
> +	QUIET_BPF_GCC  = @echo '  BPF_GCC '$@;
>  	QUIET_AR       = @echo '  AR      '$@;
>  	QUIET_LINK     = @echo '  LINK    '$@;
>  	QUIET_MKDIR    = @echo '  MKDIR   '$@;
> diff --git a/tools/scripts/utilities.mak b/tools/scripts/utilities.mak
> index d69d0345cc23..746aaf6e5145 100644
> --- a/tools/scripts/utilities.mak
> +++ b/tools/scripts/utilities.mak
> @@ -186,7 +186,7 @@ _gea_err  = $(if $(1),$(error Please set '$(1)' appropriately))
>  # was to check the flex version to see if we can use compiler warnings as
>  # errors for one of the cases flex generates code C compilers complains about.
>  
> -version-ge3 = $(shell echo "$(1).$(2)" | awk -F'.' '{ printf("%d\n", (10000000 * $$1 + 10000 * $$2 + $$3) >= (10000000 * $$4 + 10000 * $$5 + $$6)) }')
> +version-ge3 = $(shell awk -v v1="$(1)" -v v2="$(2)" 'BEGIN { split(v1, a, "."); split(v2, b, "."); printf("%d\n", (10000000 * a[1] + 10000 * a[2] + a[3]) >= (10000000 * b[1] + 10000 * b[2] + b[3])) }')
>  
>  # version-lt3
>  #
> @@ -196,4 +196,4 @@ version-ge3 = $(shell echo "$(1).$(2)" | awk -F'.' '{ printf("%d\n", (10000000 *
>  # check the flex version to see if we can use compiler warnings as errors for
>  # one of the cases flex generates code C compilers complains about.
>  
> -version-lt3 = $(shell echo "$(1).$(2)" | awk -F'.' '{ printf("%d\n", (10000000 * $$1 + 10000 * $$2 + $$3) < (10000000 * $$4 + 10000 * $$5 + $$6)) }')
> +version-lt3 = $(shell awk -v v1="$(1)" -v v2="$(2)" 'BEGIN { split(v1, a, "."); split(v2, b, "."); printf("%d\n", (10000000 * a[1] + 10000 * a[2] + a[3]) < (10000000 * b[1] + 10000 * b[2] + b[3])) }')
> -- 
> 2.56.0.307.g5fe7bd680c-goog
>