On 8/2/25 1:48 AM, Jiawei Zhao wrote:
When using GCC on x86-64 to compile an usdt prog with -O1 or higher
optimization, the compiler will generate SIB addressing mode for global
array and PC-relative addressing mode for global variable,
e.g. "1@-96(%rbp,%rax,8)" and "-1@4+t1(%rip)".
In this patch:
- force -O2 optimization for usdt.test.o to generate SIB addressing usdt
argument spec.
- change the global variable t1 to a local variable, to avoid compiler
generating PC-relative addressing mode for it.
Signed-off-by: Jiawei Zhao <phoenix500526@xxxxxxx>
---
tools/testing/selftests/bpf/Makefile | 8 ++++++++
tools/testing/selftests/bpf/prog_tests/usdt.c | 18 ++++++++++++------
2 files changed, 20 insertions(+), 6 deletions(-)
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 910d8d6402ef..4b77d06d5c42 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -759,6 +759,14 @@ TRUNNER_BPF_BUILD_RULE := $$(error no BPF objects should be built)
TRUNNER_BPF_CFLAGS :=
$(eval $(call DEFINE_TEST_RUNNER,test_maps))
+# Force usdt.c to use -O2 optimization to generate SIB addressing
+# Only apply on x86 architecture where SIB addressing is relevant
+ifeq ($(ARCH), x86)
+$(OUTPUT)/usdt.test.o: CFLAGS:=$(subst O0,O2,$(CFLAGS))
+$(OUTPUT)/cpuv4/usdt.test.o: CFLAGS:=$(subst O0,O2,$(CFLAGS))
+$(OUTPUT)/no_alu32/usdt.test.o: CFLAGS:=$(subst O0,O2,$(CFLAGS))
+endif
This is no good. You should not change from -O0 to -O2. The existing usdt.c
test should be kept. I assume at -O0 level, the compiler probably
won't generate SIB pattern.
You could add another usdt test e.g. usdt_o2.c and force
usdt_o2 is compiled with -O2 optimizations and in usdt_o2 focusing on
SIB probe.
+
# Define test_verifier test runner.
# It is much simpler than test_maps/test_progs and sufficiently different from
# them (e.g., test.h is using completely pattern), that it's worth just
diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
index 495d66414b57..86f354d25aef 100644
--- a/tools/testing/selftests/bpf/prog_tests/usdt.c
+++ b/tools/testing/selftests/bpf/prog_tests/usdt.c
@@ -14,10 +14,15 @@ static volatile int idx = 2;
static volatile __u64 bla = 0xFEDCBA9876543210ULL;
static volatile short nums[] = {-1, -2, -3, -4};
-static volatile struct {
- int x;
- signed char y;
-} t1 = { 1, -127 };
+/*
+ * TODO: At O2 optimization level, t1's USDT argument spec becomes -1@4+t1(%rip).
+ * Since libbpf doesn't support RIP addressing mode yet, this causes "unrecognized register" errors.
+ * This test will be re-enabled once libbpf supports RIP addressing mode.
+ */
+// static volatile struct {
+// int x;
+// signed char y;
+// } t1 = { 1, -127 };
[...]
