bpf: Add the get_reg_width function

Put calculation of the register value width into a dedicated function.
This function will also be used in a following commit.

Signed-off-by: Maxim Mikityanskiy <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

kernel/bpf/verifier.c

···
 	return BPF_CLASS(insn->code) == BPF_ST && BPF_MODE(insn->code) == BPF_MEM;
 }
 
+static int get_reg_width(struct bpf_reg_state *reg)
+{
+	return fls64(reg->umax_value);
+}
+
 /* check_stack_{read,write}_fixed_off functions track spill/fill of registers,
  * stack boundary and alignment are checked in check_mem_access()
  */
···
 	if (reg && !(off % BPF_REG_SIZE) && register_is_bounded(reg) && env->bpf_capable) {
 		save_register_state(env, state, spi, reg, size);
 		/* Break the relation on a narrowing spill. */
-		if (fls64(reg->umax_value) > BITS_PER_BYTE * size)
+		if (get_reg_width(reg) > BITS_PER_BYTE * size)
 			state->stack[spi].spilled_ptr.id = 0;
 	} else if (!reg && !(off % BPF_REG_SIZE) && is_bpf_st_mem(insn) &&
 		   insn->imm != 0 && env->bpf_capable) {
···
 					return -EACCES;
 				} else if (src_reg->type == SCALAR_VALUE) {
 					if (insn->off == 0) {
-						bool is_src_reg_u32 = src_reg->umax_value <= U32_MAX;
+						bool is_src_reg_u32 = get_reg_width(src_reg) <= 32;
 
 						if (is_src_reg_u32)
 							assign_scalar_id_before_mov(env, src_reg);