powerpc32/bpf: Fix codegen for bpf-to-bpf calls

Pad instructions emitted for BPF_CALL so that the number of instructions
generated does not change for different function addresses. This is
especially important for calls to other bpf functions, whose address
will only be known during extra pass.

Fixes: 51c66ad ("powerpc/bpf: Implement extended BPF on PPC32")
Cc: stable@vger.kernel.org # v5.13+
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/52d8fe51f7620a6f27f377791564d79d75463576.1641468127.git.naveen.n.rao@linux.vnet.ibm.com

Author: rnav

arch/powerpc/net/bpf_jit_comp32.c

@@ -191,6 +191,9 @@ void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 fun
 
 	if (image && rel < 0x2000000 && rel >= -0x2000000) {
 		PPC_BL_ABS(func);
+		EMIT(PPC_RAW_NOP());
+		EMIT(PPC_RAW_NOP());
+		EMIT(PPC_RAW_NOP());
 	} else {
 		/* Load function address into r0 */
 		EMIT(PPC_RAW_LIS(_R0, IMM_H(func)));