nfp: bpf: update fixup function for BPF-to-BPF calls support

Relocation for targets of BPF-to-BPF calls are required at the end of
translation. Update the nfp_fixup_branches() function in that regard.

When checking that the last instruction of each bloc is a branch, we
must account for the length of the instructions required to pop the
return address from the stack.
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

drivers/net/ethernet/netronome/nfp/bpf/jit.c

@@ -3116,7 +3116,7 @@ static int jne_reg(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 static int
 bpf_to_bpf_call(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 {
-	u32 ret_tgt, stack_depth;
+	u32 ret_tgt, stack_depth, offset_br;
 	swreg tmp_reg;
 
 	stack_depth = round_up(nfp_prog->stack_frame_depth, STACK_FRAME_ALIGN);
@@ -3160,6 +3160,7 @@ bpf_to_bpf_call(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 	ret_tgt = nfp_prog_current_offset(nfp_prog) + 3;
 	emit_br_relo(nfp_prog, BR_UNC, BR_OFF_RELO, 2,
 		     RELO_BR_GO_CALL_PUSH_REGS);
+	offset_br = nfp_prog_current_offset(nfp_prog);
 	wrp_immed_relo(nfp_prog, imm_b(nfp_prog), 0, RELO_IMMED_REL);
 	wrp_immed_relo(nfp_prog, ret_reg(nfp_prog), ret_tgt, RELO_IMMED_REL);
 
@@ -3176,6 +3177,9 @@ bpf_to_bpf_call(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 		wrp_nops(nfp_prog, 3);
 	}
 
+	meta->num_insns_after_br = nfp_prog_current_offset(nfp_prog);
+	meta->num_insns_after_br -= offset_br;
+
 	return 0;
 }
 
@@ -3344,21 +3348,36 @@ static int nfp_fixup_branches(struct nfp_prog *nfp_prog)
 	list_for_each_entry(meta, &nfp_prog->insns, l) {
 		if (meta->skip)
 			continue;
-		if (meta->insn.code == (BPF_JMP | BPF_CALL))
-			continue;
 		if (BPF_CLASS(meta->insn.code) != BPF_JMP)
 			continue;
+		if (meta->insn.code == (BPF_JMP | BPF_EXIT) &&
+		    !nfp_is_main_function(meta))
+			continue;
+		if (is_mbpf_helper_call(meta))
+			continue;
 
 		if (list_is_last(&meta->l, &nfp_prog->insns))
 			br_idx = nfp_prog->last_bpf_off;
 		else
 			br_idx = list_next_entry(meta, l)->off - 1;
 
+		/* For BPF-to-BPF function call, a stack adjustment sequence is
+		 * generated after the return instruction. Therefore, we must
+		 * withdraw the length of this sequence to have br_idx pointing
+		 * to where the "branch" NFP instruction is expected to be.
+		 */
+		if (is_mbpf_pseudo_call(meta))
+			br_idx -= meta->num_insns_after_br;
+
 		if (!nfp_is_br(nfp_prog->prog[br_idx])) {
 			pr_err("Fixup found block not ending in branch %d %02x %016llx!!\n",
 			       br_idx, meta->insn.code, nfp_prog->prog[br_idx]);
 			return -ELOOP;
 		}
+
+		if (meta->insn.code == (BPF_JMP | BPF_EXIT))
+			continue;
+
 		/* Leave special branches for later */
 		if (FIELD_GET(OP_RELO_TYPE, nfp_prog->prog[br_idx]) !=
 		    RELO_BR_REL)

drivers/net/ethernet/netronome/nfp/bpf/main.h

@@ -283,6 +283,7 @@ struct nfp_bpf_reg_state {
  * @xadd_maybe_16bit: 16bit immediate is possible
  * @jmp_dst: destination info for jump instructions
  * @jump_neg_op: jump instruction has inverted immediate, use ADD instead of SUB
+ * @num_insns_after_br: number of insns following a branch jump, used for fixup
  * @func_id: function id for call instructions
  * @arg1: arg1 for call instructions
  * @arg2: arg2 for call instructions
@@ -319,6 +320,7 @@ struct nfp_insn_meta {
 		struct {
 			struct nfp_insn_meta *jmp_dst;
 			bool jump_neg_op;
+			u32 num_insns_after_br; /* only for BPF-to-BPF calls */
 		};
 		/* function calls */
 		struct {