selftests/bpf: Fix uprobe tests in attach_probe on arm 32-bit

With test_progs compiled with ARM THUMB insns, trigger_func*() used for
testing uprobes have odd (LSB set) entry points due to interworking. This
fails alignment check first, then due to uprobe unsupported for THUMB in
prepare_uprobe() -> arch_uprobe_analyze_insn() -> arm_probes_decode_insn().

First fix by setting trigger_func*() as ARM insns and rely on interworking
enabled by default. Doesn't work on Debian bookworm target because insn #1
of funcs patched to 'UDF torvalds#25' which causes "Illegal instruction". Patched
by dynamic loader? Kernel somehow?

__attribute__((target("arm")))

Works to compile all test_progs with gcc -marm, or just attach_probe.c.

Change Makefile to compile prog_tests/attach_probe.c with '-marm' to avoid
using THUMB insns, with expected tests passing:

torvalds#8/1     attach_probe/manual-default:OK
torvalds#8/2     attach_probe/manual-legacy:OK
torvalds#8/3     attach_probe/manual-perf:OK
torvalds#8/4     attach_probe/manual-link:OK
torvalds#8/5     attach_probe/auto:OK
torvalds#8/6     attach_probe/kprobe-sleepable:OK
torvalds#8/8     attach_probe/uprobe-sleepable:OK
torvalds#8/9     attach_probe/uprobe-ref_ctr:OK
torvalds#8/10    attach_probe/uprobe-long_name:OK
torvalds#8/11    attach_probe/kprobe-long_name:OK
torvalds#8       attach_probe:OK

Note that attach_probe/uprobe-lib will still fail since it tries to attach
a uprobe to the system libc.so, which is compiled for THUMB:

test_attach_probe:PASS:skel_open 0 nsec
test_attach_probe:PASS:skel_load 0 nsec
test_attach_probe:PASS:check_bss 0 nsec
test_attach_probe:PASS:uprobe_ref_ctr_cleanup 0 nsec
libbpf: prog 'handle_uprobe_byname2': failed to create uprobe '/lib/arm-linux-gnueabihf/libc.so.6:0x528e1' perf event: -EINVAL
test_uprobe_lib:FAIL:attach_uprobe_byname2 unexpected error: -22
torvalds#8/7     attach_probe/uprobe-lib:FAIL
torvalds#8       attach_probe:FAIL

Signed-off-by: Tony Ambardar <[email protected]>

Author: guidosarducci

tools/testing/selftests/bpf/Makefile

@@ -858,6 +858,9 @@ $(OUTPUT)/uprobe_multi: uprobe_multi.c uprobe_multi.ld
 	$(Q)$(CC) $(CFLAGS) -Wl,-T,uprobe_multi.ld -O0 $(LDFLAGS) 	\
 		$(filter-out %.ld,$^) $(LDLIBS) -o $@
 
+# Avoid THUMB insns in uprobe testing since not supported
+$(OUTPUT)/attach_probe.test.o: CFLAGS += $(if $(filter arm, $(ARCH)),-marm)
+
 EXTRA_CLEAN := $(SCRATCH_DIR) $(HOST_SCRATCH_DIR)			\
 	prog_tests/tests.h map_tests/tests.h verifier/tests.h		\
 	feature bpftool $(TEST_KMOD_TARGETS)				\