[PATCH v1 1/2] perf build: Support building BPF skeletons with bpf-gcc

[Ian Rogers <irogers@google.com>]

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).

Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/Makefile.config     | 81 +++++++++++++++++++++++++++-------
 tools/perf/Makefile.perf       |  8 +++-
 tools/perf/bpf_skel.mak        | 36 ++++++++++-----
 tools/scripts/Makefile.include |  1 +
 4 files changed, 97 insertions(+), 29 deletions(-)

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index cafc7be79643..6aee2665b64c 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -662,27 +662,76 @@ 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 -dumpversion 2>/dev/null)
+        ifneq ($$(call version-lt3,$$(BPF_GCC_VERSION),14.0.0),1)
+          have_bpf_gcc := 1
+        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)
+          $(call feature_check,clang-bpf-co-re)
+          ifeq ($(feature-clang-bpf-co-re), 1)
+            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   '$@;
-- 
2.56.0.385.gd3acb90ef8-goog