selftests/bpf: Add arm target register definitions

eBPF "restricted C" code can be compiled with LLVM/clang using target
triplets like armv7l-unknown-linux-gnueabihf and loaded/run with small
cross-compiled gobpf/elf [1] programs without requiring a full BCC
port which is also undesirable on small embedded systems due to its
size footprint. The only missing pieces are these helper macros which
otherwise have to be redefined by each eBPF arm program.

[1] https://github.com/iovisor/gobpf/tree/master/elfSigned-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/bpf_helpers.h

@@ -274,6 +274,9 @@ static int (*bpf_skb_adjust_room)(void *ctx, __s32 len_diff, __u32 mode,
 #elif defined(__TARGET_ARCH_s930x)
 	#define bpf_target_s930x
 	#define bpf_target_defined
+#elif defined(__TARGET_ARCH_arm)
+	#define bpf_target_arm
+	#define bpf_target_defined
 #elif defined(__TARGET_ARCH_arm64)
 	#define bpf_target_arm64
 	#define bpf_target_defined
@@ -296,6 +299,8 @@ static int (*bpf_skb_adjust_room)(void *ctx, __s32 len_diff, __u32 mode,
 	#define bpf_target_x86
 #elif defined(__s390x__)
 	#define bpf_target_s930x
+#elif defined(__arm__)
+	#define bpf_target_arm
 #elif defined(__aarch64__)
 	#define bpf_target_arm64
 #elif defined(__mips__)
@@ -333,6 +338,19 @@ static int (*bpf_skb_adjust_room)(void *ctx, __s32 len_diff, __u32 mode,
 #define PT_REGS_SP(x) ((x)->gprs[15])
 #define PT_REGS_IP(x) ((x)->psw.addr)
 
+#elif defined(bpf_target_arm)
+
+#define PT_REGS_PARM1(x) ((x)->uregs[0])
+#define PT_REGS_PARM2(x) ((x)->uregs[1])
+#define PT_REGS_PARM3(x) ((x)->uregs[2])
+#define PT_REGS_PARM4(x) ((x)->uregs[3])
+#define PT_REGS_PARM5(x) ((x)->uregs[4])
+#define PT_REGS_RET(x) ((x)->uregs[14])
+#define PT_REGS_FP(x) ((x)->uregs[11]) /* Works only with CONFIG_FRAME_POINTER */
+#define PT_REGS_RC(x) ((x)->uregs[0])
+#define PT_REGS_SP(x) ((x)->uregs[13])
+#define PT_REGS_IP(x) ((x)->uregs[12])
+
 #elif defined(bpf_target_arm64)
 
 #define PT_REGS_PARM1(x) ((x)->regs[0])