[PATCH v2 2/2] perf build: compile BPF skeletons with -mcpu=v3

[Suchit Karunakaran]

The lock_contention BPF program uses __sync_val_compare_and_swap()
to atomically update the max_time and min_time fields in
contention_data. This builtin lowers to the BPF_CMPXCHG instruction,
which is only available in BPF ISA v3. Without an explicit -mcpu flag,
Clang targets BPF v1/v2 by default on older toolchains (Clang < 18),
causing build errors when v3 instructions are emitted.

Add -mcpu=v3 to CLANG_OPTIONS, which is used exclusively in the BPF
skeleton compilation rule.

Signed-off-by: Suchit Karunakaran <suchitkarunakaran@xxxxxxxxx>

Changes since v1:
- Moved the -mcpu=v3 addition from tools/perf/Makefile.perf to
  tools/perf/bpf_skel.mak, following the refactoring of BPF skeleton
  build logic into that file.
---
 tools/perf/bpf_skel.mak | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/bpf_skel.mak b/tools/perf/bpf_skel.mak
index 7704e7e635d8..f2559de39f96 100644
--- a/tools/perf/bpf_skel.mak
+++ b/tools/perf/bpf_skel.mak
@@ -29,7 +29,7 @@ ifneq ($(CROSS_COMPILE),)
 CLANG_TARGET_ARCH = --target=$(notdir $(CROSS_COMPILE:%-=%))
 endif
 
-CLANG_OPTIONS = -Wall
+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)
-- 
2.54.0