/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2024 Mark Johnston <markj@FreeBSD.org>
 */

#include <sys/systm.h>
#include <sys/sdt.h>

#include <machine/cpu.h>

/*
 * Return true if we can overwrite a nop at "patchpoint" with a jump to the
 * target address.
 */
bool
sdt_tracepoint_valid(uintptr_t patchpoint, uintptr_t target)
{
        int32_t offset;

        if (patchpoint == target ||
            (patchpoint & (INSN_SIZE - 1)) != 0 ||
            (target & (INSN_SIZE - 1)) != 0 ||
            patchpoint + 2 * INSN_SIZE < patchpoint)
                return (false);
        offset = target - (patchpoint + 2 * INSN_SIZE);
        if (offset < -(1 << 24) || offset > (1 << 24))
                return (false);
        return (true);
}

/*
 * Overwrite the copy of _SDT_ASM_PATCH_INSTR at the tracepoint with a jump to
 * the target address.
 */
void
sdt_tracepoint_patch(uintptr_t patchpoint, uintptr_t target)
{
        uint32_t instr;

        KASSERT(sdt_tracepoint_valid(patchpoint, target),
            ("%s: invalid tracepoint %#x -> %#x",
            __func__, patchpoint, target));

        instr =
            (((target - (patchpoint + 2 * INSN_SIZE)) >> 2) & ((1 << 24) - 1)) |
            0xea000000;
        memcpy((void *)patchpoint, &instr, sizeof(instr));
        icache_sync(patchpoint, sizeof(instr));
}

/*
 * Overwrite the patchpoint with a nop instruction.
 */
void
sdt_tracepoint_restore(uintptr_t patchpoint)
{
        uint32_t instr;

        instr = 0xe320f000u;
        memcpy((void *)patchpoint, &instr, sizeof(instr));
        icache_sync(patchpoint, sizeof(instr));
}