/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */
/*
 * Copyright (c) 2018, Joyent, Inc.  All rights reserved.
 * Copyright 2014 Nexenta Systems, Inc.  All rights reserved.
 * Copyright (c) 2013 by Delphix. All rights reserved.
 * Copyright 2025 Oxide Computer Company
 */

#include <sys/types.h>
#include <sys/reg.h>
#include <sys/privregs.h>
#include <sys/stack.h>
#include <sys/frame.h>

#include <mdb/mdb_target_impl.h>
#include <mdb/mdb_kreg_impl.h>
#include <mdb/mdb_debug.h>
#include <mdb/mdb_modapi.h>
#include <mdb/mdb_stack.h>
#include <mdb/mdb_isautil.h>
#include <mdb/mdb_amd64util.h>
#include <mdb/mdb_ctf.h>
#include <mdb/mdb_err.h>
#include <mdb/mdb.h>

#include <saveargs.h>

/*
 * This array is used by the getareg and putareg entry points, and also by our
 * register variable discipline.
 */

const mdb_tgt_regdesc_t mdb_amd64_kregs[] = {
        { "savfp", KREG_SAVFP, MDB_TGT_R_EXPORT },
        { "savpc", KREG_SAVPC, MDB_TGT_R_EXPORT },
        { "rdi", KREG_RDI, MDB_TGT_R_EXPORT },
        { "edi", KREG_RDI, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "di",  KREG_RDI, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "dil", KREG_RDI, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "rsi", KREG_RSI, MDB_TGT_R_EXPORT },
        { "esi", KREG_RSI, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "si",  KREG_RSI, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "sil", KREG_RSI, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "rdx", KREG_RDX, MDB_TGT_R_EXPORT },
        { "edx", KREG_RDX, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "dx",  KREG_RDX, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "dh",  KREG_RDX, MDB_TGT_R_EXPORT | MDB_TGT_R_8H },
        { "dl",  KREG_RDX, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "rcx", KREG_RCX, MDB_TGT_R_EXPORT },
        { "ecx", KREG_RCX, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "cx",  KREG_RCX, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "ch",  KREG_RCX, MDB_TGT_R_EXPORT | MDB_TGT_R_8H },
        { "cl",  KREG_RCX, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "r8", KREG_R8, MDB_TGT_R_EXPORT },
        { "r8d", KREG_R8,  MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "r8w", KREG_R8,  MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "r8l", KREG_R8,  MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "r9", KREG_R9, MDB_TGT_R_EXPORT },
        { "r9d", KREG_R8,  MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "r9w", KREG_R8,  MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "r9l", KREG_R8,  MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "rax", KREG_RAX, MDB_TGT_R_EXPORT },
        { "eax", KREG_RAX, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "ax",  KREG_RAX, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "ah",  KREG_RAX, MDB_TGT_R_EXPORT | MDB_TGT_R_8H },
        { "al",  KREG_RAX, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "rbx", KREG_RBX, MDB_TGT_R_EXPORT },
        { "ebx", KREG_RBX, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "bx",  KREG_RBX, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "bh",  KREG_RBX, MDB_TGT_R_EXPORT | MDB_TGT_R_8H },
        { "bl",  KREG_RBX, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "rbp", KREG_RBP, MDB_TGT_R_EXPORT },
        { "ebp", KREG_RBP, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "bp",  KREG_RBP, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "bpl", KREG_RBP, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "r10", KREG_R10, MDB_TGT_R_EXPORT },
        { "r10d", KREG_R10, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "r10w", KREG_R10, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "r10l", KREG_R10, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "r11", KREG_R11, MDB_TGT_R_EXPORT },
        { "r11d", KREG_R11, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "r11w", KREG_R11, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "r11l", KREG_R11, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "r12", KREG_R12, MDB_TGT_R_EXPORT },
        { "r12d", KREG_R12, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "r12w", KREG_R12, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "r12l", KREG_R12, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "r13", KREG_R13, MDB_TGT_R_EXPORT },
        { "r13d", KREG_R13, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "r13w", KREG_R13, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "r13l", KREG_R13, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "r14", KREG_R14, MDB_TGT_R_EXPORT },
        { "r14d", KREG_R14, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "r14w", KREG_R14, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "r14l", KREG_R14, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "r15", KREG_R15, MDB_TGT_R_EXPORT },
        { "r15d", KREG_R15, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "r15w", KREG_R15, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "r15l", KREG_R15, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "ds", KREG_DS, MDB_TGT_R_EXPORT },
        { "es", KREG_ES, MDB_TGT_R_EXPORT },
        { "fs", KREG_FS, MDB_TGT_R_EXPORT },
        { "gs", KREG_GS, MDB_TGT_R_EXPORT },
        { "trapno", KREG_TRAPNO, MDB_TGT_R_EXPORT | MDB_TGT_R_PRIV },
        { "err", KREG_ERR, MDB_TGT_R_EXPORT | MDB_TGT_R_PRIV },
        { "rip", KREG_RIP, MDB_TGT_R_EXPORT },
        { "cs", KREG_CS, MDB_TGT_R_EXPORT },
        { "rflags", KREG_RFLAGS, MDB_TGT_R_EXPORT },
        { "eflags", KREG_RFLAGS, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "rsp", KREG_RSP, MDB_TGT_R_EXPORT },
        { "esp", KREG_RSP, MDB_TGT_R_EXPORT | MDB_TGT_R_32 },
        { "sp",  KREG_RSP, MDB_TGT_R_EXPORT | MDB_TGT_R_16 },
        { "spl", KREG_RSP, MDB_TGT_R_EXPORT | MDB_TGT_R_8L },
        { "ss", KREG_SS, MDB_TGT_R_EXPORT },
        { "gsbase", KREG_GSBASE, MDB_TGT_R_EXPORT },
        { "kgsbase", KREG_KGSBASE, MDB_TGT_R_EXPORT },
        { "cr2", KREG_CR2, MDB_TGT_R_EXPORT },
        { "cr3", KREG_CR3, MDB_TGT_R_EXPORT },
        { NULL, 0, 0 }
};

void
mdb_amd64_printregs(const mdb_tgt_gregset_t *gregs)
{
        const kreg_t *kregs = &gregs->kregs[0];
        kreg_t rflags = kregs[KREG_RFLAGS];

#define GETREG2(x) ((uintptr_t)kregs[(x)]), ((uintptr_t)kregs[(x)])

        mdb_printf("%%rax = 0x%0?p %15A %%r9  = 0x%0?p %A\n",
            GETREG2(KREG_RAX), GETREG2(KREG_R9));
        mdb_printf("%%rbx = 0x%0?p %15A %%r10 = 0x%0?p %A\n",
            GETREG2(KREG_RBX), GETREG2(KREG_R10));
        mdb_printf("%%rcx = 0x%0?p %15A %%r11 = 0x%0?p %A\n",
            GETREG2(KREG_RCX), GETREG2(KREG_R11));
        mdb_printf("%%rdx = 0x%0?p %15A %%r12 = 0x%0?p %A\n",
            GETREG2(KREG_RDX), GETREG2(KREG_R12));
        mdb_printf("%%rsi = 0x%0?p %15A %%r13 = 0x%0?p %A\n",
            GETREG2(KREG_RSI), GETREG2(KREG_R13));
        mdb_printf("%%rdi = 0x%0?p %15A %%r14 = 0x%0?p %A\n",
            GETREG2(KREG_RDI), GETREG2(KREG_R14));
        mdb_printf("%%r8  = 0x%0?p %15A %%r15 = 0x%0?p %A\n\n",
            GETREG2(KREG_R8), GETREG2(KREG_R15));

        mdb_printf("%%rip = 0x%0?p %A\n", GETREG2(KREG_RIP));
        mdb_printf("%%rbp = 0x%0?p\n", kregs[KREG_RBP]);
        mdb_printf("%%rsp = 0x%0?p\n", kregs[KREG_RSP]);

        mdb_printf("%%rflags = 0x%08x\n", rflags);

        mdb_printf("  id=%u vip=%u vif=%u ac=%u vm=%u rf=%u nt=%u iopl=0x%x\n",
            (rflags & KREG_EFLAGS_ID_MASK) >> KREG_EFLAGS_ID_SHIFT,
            (rflags & KREG_EFLAGS_VIP_MASK) >> KREG_EFLAGS_VIP_SHIFT,
            (rflags & KREG_EFLAGS_VIF_MASK) >> KREG_EFLAGS_VIF_SHIFT,
            (rflags & KREG_EFLAGS_AC_MASK) >> KREG_EFLAGS_AC_SHIFT,
            (rflags & KREG_EFLAGS_VM_MASK) >> KREG_EFLAGS_VM_SHIFT,
            (rflags & KREG_EFLAGS_RF_MASK) >> KREG_EFLAGS_RF_SHIFT,
            (rflags & KREG_EFLAGS_NT_MASK) >> KREG_EFLAGS_NT_SHIFT,
            (rflags & KREG_EFLAGS_IOPL_MASK) >> KREG_EFLAGS_IOPL_SHIFT);

        mdb_printf("  status=<%s,%s,%s,%s,%s,%s,%s,%s,%s>\n\n",
            (rflags & KREG_EFLAGS_OF_MASK) ? "OF" : "of",
            (rflags & KREG_EFLAGS_DF_MASK) ? "DF" : "df",
            (rflags & KREG_EFLAGS_IF_MASK) ? "IF" : "if",
            (rflags & KREG_EFLAGS_TF_MASK) ? "TF" : "tf",
            (rflags & KREG_EFLAGS_SF_MASK) ? "SF" : "sf",
            (rflags & KREG_EFLAGS_ZF_MASK) ? "ZF" : "zf",
            (rflags & KREG_EFLAGS_AF_MASK) ? "AF" : "af",
            (rflags & KREG_EFLAGS_PF_MASK) ? "PF" : "pf",
            (rflags & KREG_EFLAGS_CF_MASK) ? "CF" : "cf");

        mdb_printf("%%cs = 0x%04x\t%%ds = 0x%04x\t"
            "%%es = 0x%04x\t%%fs = 0x%04x\n", kregs[KREG_CS], kregs[KREG_DS],
            kregs[KREG_ES], kregs[KREG_FS] & 0xffff);
        mdb_printf("%%gs = 0x%04x\t%%gsbase = 0x%lx\t%%kgsbase = 0x%lx\n",
            kregs[KREG_GS] & 0xffff, kregs[KREG_GSBASE], kregs[KREG_KGSBASE]);
        mdb_printf("%%trapno = 0x%x\t%%err = 0x%x\t%%cr2 = 0x%lx\t"
            "%%cr3 = 0x%lx\n", kregs[KREG_TRAPNO], kregs[KREG_ERR],
            kregs[KREG_CR2], kregs[KREG_CR3]);
}

int
mdb_amd64_kvm_stack_iter(mdb_tgt_t *t, const mdb_tgt_gregset_t *gsp,
    mdb_tgt_stack_f *func, void *arg)
{
        mdb_tgt_gregset_t gregs;
        kreg_t *kregs = &gregs.kregs[0];
        int got_pc = (gsp->kregs[KREG_RIP] != 0);
        uint_t argc, reg_argc;
        long fr_argv[32];
        int start_index; /* index to save_instr where to start comparison */
        int err;
        int i;

        struct fr {
                uintptr_t fr_savfp;
                uintptr_t fr_savpc;
        } fr;

        uintptr_t fp = gsp->kregs[KREG_RBP];
        uintptr_t pc = gsp->kregs[KREG_RIP];
        uintptr_t lastfp = 0;

        ssize_t size;
        ssize_t insnsize;
        uint8_t ins[SAVEARGS_INSN_SEQ_LEN];

        GElf_Sym s;
        mdb_syminfo_t sip;
        mdb_ctf_funcinfo_t mfp;
        int xpv_panic = 0;
        int advance_tortoise = 1;
        uintptr_t tortoise_fp = 0;
#ifndef _KMDB
        int xp;

        if ((mdb_readsym(&xp, sizeof (xp), "xpv_panicking") != -1) && (xp > 0))
                xpv_panic = 1;
#endif

        bcopy(gsp, &gregs, sizeof (gregs));

        while (fp != 0) {
                int args_style = 0;

                if (mdb_tgt_aread(t, MDB_TGT_AS_VIRT_S, &fr, sizeof (fr), fp) !=
                    sizeof (fr)) {
                        err = EMDB_NOMAP;
                        goto badfp;
                }

                if (tortoise_fp == 0) {
                        tortoise_fp = fp;
                } else {
                        /*
                         * Advance tortoise_fp every other frame, so we detect
                         * cycles with Floyd's tortoise/hare.
                         */
                        if (advance_tortoise != 0) {
                                struct fr tfr;

                                if (mdb_tgt_aread(t, MDB_TGT_AS_VIRT_S, &tfr,
                                    sizeof (tfr), tortoise_fp) !=
                                    sizeof (tfr)) {
                                        err = EMDB_NOMAP;
                                        goto badfp;
                                }

                                tortoise_fp = tfr.fr_savfp;
                        }

                        if (fp == tortoise_fp) {
                                err = EMDB_STKFRAME;
                                goto badfp;
                        }
                }

                advance_tortoise = !advance_tortoise;

                if ((mdb_tgt_lookup_by_addr(t, pc, MDB_TGT_SYM_FUZZY,
                    NULL, 0, &s, &sip) == 0) &&
                    (mdb_ctf_func_info(&s, &sip, &mfp) == 0)) {
                        int return_type = mdb_ctf_type_kind(mfp.mtf_return);
                        mdb_ctf_id_t args_types[5];

                        argc = mfp.mtf_argc;

                        /*
                         * If the function returns a structure or union
                         * greater than 16 bytes in size %rdi contains the
                         * address in which to store the return value rather
                         * than for an argument.
                         */
                        if ((return_type == CTF_K_STRUCT ||
                            return_type == CTF_K_UNION) &&
                            mdb_ctf_type_size(mfp.mtf_return) > 16)
                                start_index = 1;
                        else
                                start_index = 0;

                        /*
                         * If any of the first 5 arguments are a structure
                         * less than 16 bytes in size, it will be passed
                         * spread across two argument registers, and we will
                         * not cope.
                         */
                        if (mdb_ctf_func_args(&mfp, 5, args_types) == CTF_ERR)
                                argc = 0;

                        for (i = 0; i < MIN(5, argc); i++) {
                                int t = mdb_ctf_type_kind(args_types[i]);

                                if (((t == CTF_K_STRUCT) ||
                                    (t == CTF_K_UNION)) &&
                                    mdb_ctf_type_size(args_types[i]) <= 16) {
                                        argc = 0;
                                        break;
                                }
                        }
                } else {
                        argc = 0;
                }

                /*
                 * The number of instructions to search for argument saving is
                 * limited such that only instructions prior to %pc are
                 * considered such that we never read arguments from a
                 * function where the saving code has not in fact yet
                 * executed.
                 */
                insnsize = MIN(MIN(s.st_size, SAVEARGS_INSN_SEQ_LEN),
                    pc - s.st_value);

                if (mdb_tgt_aread(t, MDB_TGT_AS_VIRT_I, ins, insnsize,
                    s.st_value) != insnsize)
                        argc = 0;

                if ((argc != 0) &&
                    ((args_style = saveargs_has_args(ins, insnsize, argc,
                    start_index)) != SAVEARGS_NO_ARGS)) {
                        /* Up to 6 arguments are passed via registers */
                        reg_argc = MIN((6 - start_index), mfp.mtf_argc);
                        size = reg_argc * sizeof (long);

                        /*
                         * If Studio pushed a structure return address as an
                         * argument, we need to read one more argument than
                         * actually exists (the addr) to make everything line
                         * up.
                         */
                        if (args_style == SAVEARGS_STRUCT_ARGS)
                                size += sizeof (long);

                        if (mdb_tgt_aread(t, MDB_TGT_AS_VIRT_S, fr_argv, size,
                            (fp - size)) != size)
                                return (-1);    /* errno has been set for us */

                        /*
                         * Arrange the arguments in the right order for
                         * printing.
                         */
                        for (i = 0; i < (reg_argc / 2); i++) {
                                long t = fr_argv[i];

                                fr_argv[i] = fr_argv[reg_argc - i - 1];
                                fr_argv[reg_argc - i - 1] = t;
                        }

                        if (argc > reg_argc) {
                                size = MIN((argc - reg_argc) * sizeof (long),
                                    sizeof (fr_argv) -
                                    (reg_argc * sizeof (long)));

                                if (mdb_tgt_aread(t, MDB_TGT_AS_VIRT_S,
                                    &fr_argv[reg_argc], size,
                                    fp + sizeof (fr)) != size)
                                        return (-1); /* errno has been set */
                        }
                } else {
                        argc = 0;
                }

                if (got_pc && func(arg, pc, argc, fr_argv, &gregs) != 0)
                        break;

                kregs[KREG_RSP] = kregs[KREG_RBP];

                lastfp = fp;
                fp = fr.fr_savfp;
                /*
                 * The Xen hypervisor marks a stack frame as belonging to
                 * an exception by inverting the bits of the pointer to
                 * that frame.  We attempt to identify these frames by
                 * inverting the pointer and seeing if it is within 0xfff
                 * bytes of the last frame.
                 */
                if (xpv_panic)
                        if ((fp != 0) && (fp < lastfp) &&
                            ((lastfp ^ ~fp) < 0xfff))
                                fp = ~fp;

                kregs[KREG_RBP] = fp;
                kregs[KREG_RIP] = pc = fr.fr_savpc;

                got_pc = (pc != 0);
        }

        return (0);

badfp:
        mdb_printf("%p [%s]", fp, mdb_strerror(err));
        return (set_errno(err));
}

/*
 * Determine the return address for the current frame.  Typically this is the
 * fr_savpc value from the current frame, but we also perform some special
 * handling to see if we are stopped on one of the first two instructions of
 * a typical function prologue, in which case %rbp will not be set up yet.
 */
int
mdb_amd64_step_out(mdb_tgt_t *t, uintptr_t *p, kreg_t pc, kreg_t fp, kreg_t sp,
    mdb_instr_t curinstr)
{
        struct frame fr;
        GElf_Sym s;
        char buf[1];

        enum {
                M_PUSHQ_RBP     = 0x55, /* pushq %rbp */
                M_REX_W         = 0x48, /* REX prefix with only W set */
                M_MOVL_RBP      = 0x8b  /* movq %rsp, %rbp with prefix */
        };

        if (mdb_tgt_lookup_by_addr(t, pc, MDB_TGT_SYM_FUZZY,
            buf, 0, &s, NULL) == 0) {
                if (pc == s.st_value && curinstr == M_PUSHQ_RBP)
                        fp = sp - 8;
                else if (pc == s.st_value + 1 && curinstr == M_REX_W) {
                        if (mdb_tgt_aread(t, MDB_TGT_AS_VIRT_I, &curinstr,
                            sizeof (curinstr), pc + 1) == sizeof (curinstr) &&
                            curinstr == M_MOVL_RBP)
                                fp = sp;
                }
        }

        if (mdb_tgt_aread(t, MDB_TGT_AS_VIRT_S, &fr, sizeof (fr), fp) ==
            sizeof (fr)) {
                *p = fr.fr_savpc;
                return (0);
        }

        return (-1); /* errno is set for us */
}

/*ARGSUSED*/
int
mdb_amd64_next(mdb_tgt_t *t, uintptr_t *p, kreg_t pc, mdb_instr_t curinstr)
{
        mdb_tgt_addr_t npc;
        mdb_tgt_addr_t callpc;

        enum {
                M_CALL_REL = 0xe8, /* call near with relative displacement */
                M_CALL_REG = 0xff, /* call near indirect or call far register */

                M_REX_LO = 0x40,
                M_REX_HI = 0x4f
        };

        /*
         * If the opcode is a near call with relative displacement, assume the
         * displacement is a rel32 from the next instruction.
         */
        if (curinstr == M_CALL_REL) {
                *p = pc + sizeof (mdb_instr_t) + sizeof (uint32_t);
                return (0);
        }

        /* Skip the rex prefix, if any */
        callpc = pc;
        while (curinstr >= M_REX_LO && curinstr <= M_REX_HI) {
                if (mdb_tgt_aread(t, MDB_TGT_AS_VIRT_I, &curinstr,
                    sizeof (curinstr), ++callpc) != sizeof (curinstr))
                        return (-1); /* errno is set for us */
        }

        if (curinstr != M_CALL_REG) {
                /* It's not a call */
                return (set_errno(EAGAIN));
        }

        npc = mdb_dis_nextins(mdb.m_disasm, t, MDB_TGT_AS_VIRT_I, pc);
        if (npc == pc)
                return (-1); /* errno is set for us */

        *p = npc;
        return (0);
}

int
mdb_amd64_kvm_frame(void *argp, uintptr_t pc, uint_t argc, const long *argv,
    const mdb_tgt_gregset_t *gregs)
{
        mdb_stack_frame_hdl_t *hdl = argp;
        uint64_t bp;

        bp = gregs->kregs[KREG_RBP];
        mdb_stack_frame(hdl, pc, bp, argc, argv);
        return (0);
}

/*
 * Check if the instruction immediately before the given program counter (pcp)
 * is a CALL instruction on AMD64. Since x86-64 instructions are
 * variable-length, we read the 8 bytes preceding the PC and look for specific
 * call encodings at known offsets that would align with common call
 * instruction lengths. Although x86 instructions can be up to 15 bytes long,
 * for a CALL to reach that length would require a long sequence of prefixes.
 * Of those, only the address-size prefix would affect where we need to look
 * for the instruction, and such prefixes are extremely rare in real-world
 * code.
 */
boolean_t
mdb_amd64_prev_callcheck(uintptr_t pcp)
{
        uint8_t buf[8];

        /*
         * Ensure we can read 8 bytes before the PC. This accommodates the
         * largest call encoding we care about (far calls).
         */
        if (pcp < 8 || mdb_vread(buf, sizeof (buf), pcp - 8) != sizeof (buf))
                return (B_FALSE);

        /*
         * Direct near call: CALL rel32
         * Opcode: E8, followed by 4-byte PC-relative offset.
         * Instruction is 5 bytes long; opcode is at buf[3].
         */
        if (buf[3] == 0xe8)
                return (B_TRUE);

        /*
         * Indirect near call: CALL r/m64
         * Opcode: FF /2 (i.e., reg field of ModR/M is 010).
         *
         * We're expecting the instruction to be exactly 2 bytes: FF 14,
         * with opcode at buf[5] and ModR/M at buf[6].
         *
         * buf[6] == 0x14 means:
         *  - mod = 00 (no displacement)
         *  - reg = 010 (CALL)
         *  - r/m = 100 (SIB follows — typically [rsp])
         *
         * This form is common in PLT stubs like: CALL QWORD PTR [RSP]
         *
         * Other encodings of FF /2 are less plausible here:
         *  - mod = 01 - 8-bit displacement - unlikely for noreturn functions
         *  - mod = 10 - 32-bit displacement - would overlap with PC; invalid
         *  - mod = 00 with r/m != 100 - e.g., CALL RAX - would return to
         *    buf[7], not pcp
         */
        if (buf[5] == 0xff && buf[6] == 0x14)
                return (B_TRUE);

        /*
         * Indirect RIP-relative call: CALL QWORD PTR [RIP + disp32]
         * Encoding: FF 15 xx xx xx xx
         * Instruction is 6 bytes long; opcode at buf[2], ModR/M at buf[3].
         * Common in PLT thunks and PIC code.
         */
        if (buf[2] == 0xff && buf[3] == 0x15)
                return (B_TRUE);

        /*
         * Far call (segment-based): CALL FAR ptr16:32
         * Opcode: 9A, followed by 6-byte far pointer.
         * Rare in modern 64-bit code but still valid.
         * Instruction is 7 bytes; opcode at buf[0].
         */
        if (buf[0] == 0x9a)
                return (B_TRUE);

        return (B_FALSE);
}