target/arm/mte_helper.c

/*
 * ARM v8.5-MemTag Operations
 *
 * Copyright (c) 2020 Linaro, Ltd.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
 */

#include "qemu/osdep.h"
#include "cpu.h"
#include "internals.h"
#include "exec/exec-all.h"
#include "exec/cpu_ldst.h"
#include "exec/helper-proto.h"


static int choose_nonexcluded_tag(int tag, int offset, uint16_t exclude)
{
    if (exclude == 0xffff) {
        return 0;
    }
    if (offset == 0) {
        while (exclude & (1 << tag)) {
            tag = (tag + 1) & 15;
        }
    } else {
        do {
            do {
                tag = (tag + 1) & 15;
            } while (exclude & (1 << tag));
        } while (--offset > 0);
    }
    return tag;
}

uint64_t HELPER(irg)(CPUARMState *env, uint64_t rn, uint64_t rm)
{
    int rtag;

    /*
     * Our IMPDEF choice for GCR_EL1.RRND==1 is to behave as if
     * GCR_EL1.RRND==0, always producing deterministic results.
     */
    uint16_t exclude = extract32(rm | env->cp15.gcr_el1, 0, 16);
    int start = extract32(env->cp15.rgsr_el1, 0, 4);
    int seed = extract32(env->cp15.rgsr_el1, 8, 16);
    int offset, i;

    /* RandomTag */
    for (i = offset = 0; i < 4; ++i) {
        /* NextRandomTagBit */
        int top = (extract32(seed, 5, 1) ^ extract32(seed, 3, 1) ^
                   extract32(seed, 2, 1) ^ extract32(seed, 0, 1));
        seed = (top << 15) | (seed >> 1);
        offset |= top << i;
    }
    rtag = choose_nonexcluded_tag(start, offset, exclude);
    env->cp15.rgsr_el1 = rtag | (seed << 8);

    return address_with_allocation_tag(rn, rtag);
}