powerpc64/bpf: Add support for indirect jump

Add support for a new instruction

	BPF_JMP|BPF_X|BPF_JA, SRC=0, DST=Rx, off=0, imm=0

which does an indirect jump to a location stored in Rx. The
register Rx should have type PTR_TO_INSN. This new type ensures
that the Rx register contains a value (or a range of values)
loaded from a correct jump table – map of type instruction array.

Support indirect jump to all registers in powerpc64 JIT using
the ctr register. Move Rx content to ctr register, then invoke
bctr instruction to branch to address stored in ctr register.
Skip save and restore of TOC as the jump is always within the
program context.

Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>
Acked-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260401152133.42544-4-adubey@linux.ibm.com

Author: Abhishek Dubey

arch/powerpc/net/bpf_jit_comp64.c

@@ -1708,6 +1708,14 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
 			addrs[++i] = ctx->idx * 4;
 			break;
 
+		/*
+		 * JUMP reg
+		 */
+		case BPF_JMP | BPF_JA | BPF_X:
+			EMIT(PPC_RAW_MTCTR(dst_reg));
+			EMIT(PPC_RAW_BCTR());
+			break;
+
 		/*
 		 * Return/Exit
 		 */