diff mbox

[v3,05/21] RISC-V CPU Helpers

Message ID 1515637324-96034-6-git-send-email-mjc@sifive.com (mailing list archive)
State New, archived
Headers show

Commit Message

Michael Clark Jan. 11, 2018, 2:21 a.m. UTC
Privileged control and status register helpers and page fault handling.

Signed-off-by: Michael Clark <mjc@sifive.com>
---
 target/riscv/helper.c    | 499 ++++++++++++++++++++++++++++++++++
 target/riscv/helper.h    |  78 ++++++
 target/riscv/op_helper.c | 682 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 1259 insertions(+)
 create mode 100644 target/riscv/helper.c
 create mode 100644 target/riscv/helper.h
 create mode 100644 target/riscv/op_helper.c

Comments

Richard Henderson Jan. 11, 2018, 3:29 p.m. UTC | #1
On 01/10/2018 06:21 PM, Michael Clark wrote:
> +    int ptshift = (levels - 1) * ptidxbits;
> +    int i;
> +    for (i = 0; i < levels; i++, ptshift -= ptidxbits) {
> +        target_ulong idx = (addr >> (PGSHIFT + ptshift)) &
> +                           ((1 << ptidxbits) - 1);
> +
> +        /* check that physical address of PTE is legal */
> +        target_ulong pte_addr = base + idx * ptesize;
> +        target_ulong pte = ldq_phys(cs->as, pte_addr);
> +        target_ulong ppn = pte >> PTE_PPN_SHIFT;
> +
> +        if (PTE_TABLE(pte)) { /* next level of page table */
> +            base = ppn << PGSHIFT;
> +        } else if ((pte & PTE_U) ? (mode == PRV_S) && !sum : !(mode == PRV_S)) {
> +            break;
> +        } else if (!(pte & PTE_V) || (!(pte & PTE_R) && (pte & PTE_W))) {
> +            break;

It might be clearer to return TRANSLATION_FAILED directly here.

> +        } else if (access_type == MMU_INST_FETCH ? !(pte & PTE_X) :
> +                  access_type == MMU_DATA_LOAD ?  !(pte & PTE_R) &&
> +                  !(mxr && (pte & PTE_X)) : !((pte & PTE_R) && (pte & PTE_W))) {
> +            break;

It might be clearer to pre-compute the access required and the access granted
by this page table level.  E.g. before the loop

  access_requested = (access_type == MMU_INST_FETCH ? PTE_X
                      : access_type == MMU_DATA_LOAD ? PTE_R : PTE_W);

and then here

  access_granted = pte & (PTE_X | PTE_R | PTE_W);
  if (mxr && (pte & PTE_X)) {
    access_granted |= PTE_R;
  }
  if ((access_requested & access_granted) == 0) {
    return TRANSLATION_FAILED;
  }

> +            /* set accessed and possibly dirty bits.
> +               we only put it in the TLB if it has the right stuff */
> +            stq_phys(cs->as, pte_addr, ldq_phys(cs->as, pte_addr) | PTE_A |
> +                    ((access_type == MMU_DATA_STORE) * PTE_D));

Surely you only want to do this if the bits in question are not already set.

You want

    set_bits = PTE_A + (access_type == MMU_DATA_STORE) * PTE_D);
    if ((pte & set_bits) != set_bits) {
        stq_phys(...);
        pte |= set_bits;  /* see below */
    }

> +            /* we do not give all prots indicated by the PTE
> +             * this is because future accesses need to do things like set the
> +             * dirty bit on the PTE
> +             *
> +             * at this point, we assume that protection checks have occurred */
> +            if (mode == PRV_S) {
> +                if ((pte & PTE_X) && access_type == MMU_INST_FETCH) {
> +                    *prot |= PAGE_EXEC;
> +                } else if ((pte & PTE_W) && access_type == MMU_DATA_STORE) {
> +                    *prot |= PAGE_WRITE;
> +                } else if ((pte & PTE_R) && access_type == MMU_DATA_LOAD) {
> +                    *prot |= PAGE_READ;
> +                } else {
> +                    g_assert_not_reached();
> +                }
> +            } else {
> +                if ((pte & PTE_X) && access_type == MMU_INST_FETCH) {
> +                    *prot |= PAGE_EXEC;
> +                } else if ((pte & PTE_W) && access_type == MMU_DATA_STORE) {
> +                    *prot |= PAGE_WRITE;
> +                } else if ((pte & PTE_R) && access_type == MMU_DATA_LOAD) {
> +                    *prot |= PAGE_READ;
> +                } else {
> +                    g_assert_not_reached();
> +                }
> +            }

This is wrong.  First, it isn't taking MXR into account.  Second, you don't
want to only grant what is required by the access, but also what is allowable.
Otherwise we will keep coming back to this routine any different kind of
access.  Third, what has PRV_S got to do with it?

You want

  /* If the dirty bit is not yet set, remove write permission from
     the page so that we come back here to set it.  */
  if ((pte & PTE_D) == 0) {
    access_granted &= ~PTE_W;
  }

  *prot = (access_granted & PTE_X ? PAGE_EXEC : 0)
        | (access_granted & PTE_R ? PAGE_READ : 0)
        | (access_granted & PTE_W ? PAGE_WRITE : 0);


Did I miss the check for misaligned superpages (step 6 in 4.3.2
Virtual Address Translation Process)?


> +/*
> + * Handle writes to CSRs and any resulting special behavior
> + *
> + * Adapted from Spike's processor_t::set_csr
> + */
> +inline void csr_write_helper(CPURISCVState *env, target_ulong val_to_write,
> +        target_ulong csrno)

Again, drop the inline.  (This is a huge function anyway, why would you want that?)

> +inline target_ulong csr_read_helper(CPURISCVState *env, target_ulong csrno)

Likewise.

> +target_ulong helper_sret(CPURISCVState *env, target_ulong cpu_pc_deb)
> +{
> +    if (!(env->priv >= PRV_S)) {
> +        helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
> +    }

Again, I strongly suspect that you need to be using an unwinding exception
here, and elsewhere within this file.  Otherwise the PC against which the
exception is reported will be wrong.


r~
diff mbox

Patch

diff --git a/target/riscv/helper.c b/target/riscv/helper.c
new file mode 100644
index 0000000..ff3f19a
--- /dev/null
+++ b/target/riscv/helper.c
@@ -0,0 +1,499 @@ 
+/*
+ *  RISC-V emulation helpers for qemu.
+ *
+ *  Author: Sagar Karandikar, sagark@eecs.berkeley.edu
+ *
+ *
+ * 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 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 "qemu/log.h"
+#include "cpu.h"
+#include "exec/exec-all.h"
+
+#define RISCV_DEBUG_INTERRUPT 0
+
+int riscv_cpu_mmu_index(CPURISCVState *env, bool ifetch)
+{
+#ifdef CONFIG_USER_ONLY
+    return 0;
+#else
+    target_ulong mode = env->priv;
+    if (!ifetch) {
+        if (get_field(env->mstatus, MSTATUS_MPRV)) {
+            mode = get_field(env->mstatus, MSTATUS_MPP);
+        }
+    }
+    if (env->priv_ver >= PRIV_VERSION_1_10_0) {
+        if (get_field(env->satp, SATP_MODE) == VM_1_10_MBARE) {
+            mode = PRV_M;
+        }
+    } else {
+        if (get_field(env->mstatus, MSTATUS_VM) == VM_1_09_MBARE) {
+            mode = PRV_M;
+        }
+    }
+    return mode;
+#endif
+}
+
+#ifndef CONFIG_USER_ONLY
+/*
+ * Return RISC-V IRQ number if an interrupt should be taken, else -1.
+ * Used in cpu-exec.c
+ *
+ * Adapted from Spike's processor_t::take_interrupt()
+ */
+static int riscv_cpu_hw_interrupts_pending(CPURISCVState *env)
+{
+    target_ulong pending_interrupts = env->mip & env->mie;
+
+    target_ulong mie = get_field(env->mstatus, MSTATUS_MIE);
+    target_ulong m_enabled = env->priv < PRV_M || (env->priv == PRV_M && mie);
+    target_ulong enabled_interrupts = pending_interrupts &
+                                      ~env->mideleg & -m_enabled;
+
+    target_ulong sie = get_field(env->mstatus, MSTATUS_SIE);
+    target_ulong s_enabled = env->priv < PRV_S || (env->priv == PRV_S && sie);
+    enabled_interrupts |= pending_interrupts & env->mideleg &
+                          -s_enabled;
+
+    if (enabled_interrupts) {
+        target_ulong counted = ctz64(enabled_interrupts); /* since non-zero */
+        if (counted == IRQ_X_HOST) {
+            /* we're handing it to the cpu now, so get rid of the qemu irq */
+            qemu_irq_lower(HTIF_IRQ);
+        } else if (counted == IRQ_M_TIMER) {
+            /* we're handing it to the cpu now, so get rid of the qemu irq */
+            qemu_irq_lower(MTIP_IRQ);
+        } else if (counted == IRQ_S_TIMER || counted == IRQ_H_TIMER) {
+            /* don't lower irq here */
+        }
+        return counted;
+    } else {
+        return EXCP_NONE; /* indicates no pending interrupt */
+    }
+}
+#endif
+
+bool riscv_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
+{
+#if !defined(CONFIG_USER_ONLY)
+    if (interrupt_request & CPU_INTERRUPT_HARD) {
+        RISCVCPU *cpu = RISCV_CPU(cs);
+        CPURISCVState *env = &cpu->env;
+        int interruptno = riscv_cpu_hw_interrupts_pending(env);
+        if (interruptno + 1) {
+            cs->exception_index = RISCV_EXCP_INT_FLAG | interruptno;
+            riscv_cpu_do_interrupt(cs);
+            return true;
+        }
+    }
+#endif
+    return false;
+}
+
+#if !defined(CONFIG_USER_ONLY)
+
+/* get_physical_address - get the physical address for this virtual address
+ *
+ * Do a page table walk to obtain the physical address corresponding to a
+ * virtual address. Returns 0 if the translation was successful
+ *
+ * Adapted from Spike's mmu_t::translate and mmu_t::walk
+ *
+ */
+static int get_physical_address(CPURISCVState *env, hwaddr *physical,
+                                int *prot, target_ulong address,
+                                int access_type, int mmu_idx)
+{
+    /* NOTE: the env->pc value visible here will not be
+     * correct, but the value visible to the exception handler
+     * (riscv_cpu_do_interrupt) is correct */
+
+    const int mode = mmu_idx;
+
+    *prot = 0;
+    CPUState *cs = CPU(riscv_env_get_cpu(env));
+
+    if (mode == PRV_M) {
+        *physical = address;
+        *prot = PAGE_READ | PAGE_WRITE | PAGE_EXEC;
+        return TRANSLATE_SUCCESS;
+    }
+
+    target_ulong addr = address;
+    target_ulong base;
+
+    int levels, ptidxbits, ptesize, vm, sum;
+    int mxr = get_field(env->mstatus, MSTATUS_MXR);
+
+    if (env->priv_ver >= PRIV_VERSION_1_10_0) {
+        base = get_field(env->satp, SATP_PPN) << PGSHIFT;
+        sum = get_field(env->mstatus, MSTATUS_SUM);
+        vm = get_field(env->satp, SATP_MODE);
+        switch (vm) {
+        case VM_1_10_SV32:
+          levels = 2; ptidxbits = 10; ptesize = 4; break;
+        case VM_1_10_SV39:
+          levels = 3; ptidxbits = 9; ptesize = 8; break;
+        case VM_1_10_SV48:
+          levels = 4; ptidxbits = 9; ptesize = 8; break;
+        case VM_1_10_SV57:
+          levels = 5; ptidxbits = 9; ptesize = 8; break;
+        case VM_1_10_MBARE:
+          /* cpu_mmu_index returns PRV_M for S-Mode bare */
+        default:
+          g_assert_not_reached();
+        }
+    } else {
+        base = env->sptbr << PGSHIFT;
+        sum = !get_field(env->mstatus, MSTATUS_PUM);
+        vm = get_field(env->mstatus, MSTATUS_VM);
+        switch (vm) {
+        case VM_1_09_SV32:
+          levels = 2; ptidxbits = 10; ptesize = 4; break;
+        case VM_1_09_SV39:
+          levels = 3; ptidxbits = 9; ptesize = 8; break;
+        case VM_1_09_SV48:
+          levels = 4; ptidxbits = 9; ptesize = 8; break;
+        case VM_1_09_MBARE:
+          /* cpu_mmu_index returns PRV_M for S-Mode bare */
+        default:
+          g_assert_not_reached();
+        }
+    }
+
+    int va_bits = PGSHIFT + levels * ptidxbits;
+    target_ulong mask = (1L << (TARGET_LONG_BITS - (va_bits - 1))) - 1;
+    target_ulong masked_msbs = (addr >> (va_bits - 1)) & mask;
+    if (masked_msbs != 0 && masked_msbs != mask) {
+        return TRANSLATE_FAIL;
+    }
+
+    int ptshift = (levels - 1) * ptidxbits;
+    int i;
+    for (i = 0; i < levels; i++, ptshift -= ptidxbits) {
+        target_ulong idx = (addr >> (PGSHIFT + ptshift)) &
+                           ((1 << ptidxbits) - 1);
+
+        /* check that physical address of PTE is legal */
+        target_ulong pte_addr = base + idx * ptesize;
+        target_ulong pte = ldq_phys(cs->as, pte_addr);
+        target_ulong ppn = pte >> PTE_PPN_SHIFT;
+
+        if (PTE_TABLE(pte)) { /* next level of page table */
+            base = ppn << PGSHIFT;
+        } else if ((pte & PTE_U) ? (mode == PRV_S) && !sum : !(mode == PRV_S)) {
+            break;
+        } else if (!(pte & PTE_V) || (!(pte & PTE_R) && (pte & PTE_W))) {
+            break;
+        } else if (access_type == MMU_INST_FETCH ? !(pte & PTE_X) :
+                  access_type == MMU_DATA_LOAD ?  !(pte & PTE_R) &&
+                  !(mxr && (pte & PTE_X)) : !((pte & PTE_R) && (pte & PTE_W))) {
+            break;
+        } else {
+            /* set accessed and possibly dirty bits.
+               we only put it in the TLB if it has the right stuff */
+            stq_phys(cs->as, pte_addr, ldq_phys(cs->as, pte_addr) | PTE_A |
+                    ((access_type == MMU_DATA_STORE) * PTE_D));
+
+            /* for superpage mappings, make a fake leaf PTE for the TLB's
+               benefit. */
+            target_ulong vpn = addr >> PGSHIFT;
+            *physical = (ppn | (vpn & ((1L << ptshift) - 1))) << PGSHIFT;
+
+            /* we do not give all prots indicated by the PTE
+             * this is because future accesses need to do things like set the
+             * dirty bit on the PTE
+             *
+             * at this point, we assume that protection checks have occurred */
+            if (mode == PRV_S) {
+                if ((pte & PTE_X) && access_type == MMU_INST_FETCH) {
+                    *prot |= PAGE_EXEC;
+                } else if ((pte & PTE_W) && access_type == MMU_DATA_STORE) {
+                    *prot |= PAGE_WRITE;
+                } else if ((pte & PTE_R) && access_type == MMU_DATA_LOAD) {
+                    *prot |= PAGE_READ;
+                } else {
+                    g_assert_not_reached();
+                }
+            } else {
+                if ((pte & PTE_X) && access_type == MMU_INST_FETCH) {
+                    *prot |= PAGE_EXEC;
+                } else if ((pte & PTE_W) && access_type == MMU_DATA_STORE) {
+                    *prot |= PAGE_WRITE;
+                } else if ((pte & PTE_R) && access_type == MMU_DATA_LOAD) {
+                    *prot |= PAGE_READ;
+                } else {
+                    g_assert_not_reached();
+                }
+            }
+            return TRANSLATE_SUCCESS;
+        }
+    }
+    return TRANSLATE_FAIL;
+}
+
+static void raise_mmu_exception(CPURISCVState *env, target_ulong address,
+                                MMUAccessType access_type)
+{
+    CPUState *cs = CPU(riscv_env_get_cpu(env));
+    int page_fault_exceptions =
+        (env->priv_ver >= PRIV_VERSION_1_10_0) &&
+        get_field(env->satp, SATP_MODE) != VM_1_10_MBARE;
+    int exception = 0;
+    if (access_type == MMU_INST_FETCH) { /* inst access */
+        exception = page_fault_exceptions ?
+            RISCV_EXCP_INST_PAGE_FAULT : RISCV_EXCP_INST_ACCESS_FAULT;
+        env->badaddr = address;
+    } else if (access_type == MMU_DATA_STORE) { /* store access */
+        exception = page_fault_exceptions ?
+            RISCV_EXCP_STORE_PAGE_FAULT : RISCV_EXCP_STORE_AMO_ACCESS_FAULT;
+        env->badaddr = address;
+    } else if (access_type == MMU_DATA_LOAD) { /* load access */
+        exception = page_fault_exceptions ?
+            RISCV_EXCP_LOAD_PAGE_FAULT : RISCV_EXCP_LOAD_ACCESS_FAULT;
+        env->badaddr = address;
+    } else {
+        g_assert_not_reached();
+    }
+    cs->exception_index = exception;
+}
+
+hwaddr riscv_cpu_get_phys_page_debug(CPUState *cs, vaddr addr)
+{
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    hwaddr phys_addr;
+    int prot;
+    int mem_idx = cpu_mmu_index(&cpu->env, false);
+
+    if (get_physical_address(&cpu->env, &phys_addr, &prot, addr, 0, mem_idx)) {
+        return -1;
+    }
+    return phys_addr;
+}
+
+void riscv_cpu_do_unaligned_access(CPUState *cs, vaddr addr,
+                                   MMUAccessType access_type, int mmu_idx,
+                                   uintptr_t retaddr)
+{
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    CPURISCVState *env = &cpu->env;
+    if (access_type == MMU_INST_FETCH) {
+        cs->exception_index = RISCV_EXCP_INST_ADDR_MIS;
+        env->badaddr = addr;
+    } else if (access_type == MMU_DATA_STORE) {
+        cs->exception_index = RISCV_EXCP_STORE_AMO_ADDR_MIS;
+        env->badaddr = addr;
+    } else if (access_type == MMU_DATA_LOAD) {
+        cs->exception_index = RISCV_EXCP_LOAD_ADDR_MIS;
+        env->badaddr = addr;
+    } else {
+        g_assert_not_reached();
+    }
+    do_raise_exception_err(env, cs->exception_index, retaddr);
+}
+
+/* called by qemu's softmmu to fill the qemu tlb */
+void tlb_fill(CPUState *cs, target_ulong addr, MMUAccessType access_type,
+        int mmu_idx, uintptr_t retaddr)
+{
+    int ret;
+    ret = riscv_cpu_handle_mmu_fault(cs, addr, access_type, mmu_idx);
+    if (ret == TRANSLATE_FAIL) {
+        RISCVCPU *cpu = RISCV_CPU(cs);
+        CPURISCVState *env = &cpu->env;
+        do_raise_exception_err(env, cs->exception_index, retaddr);
+    }
+}
+
+void riscv_cpu_unassigned_access(CPUState *cs, hwaddr addr, bool is_write,
+        bool is_exec, int unused, unsigned size)
+{
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    CPURISCVState *env = &cpu->env;
+    if (is_exec) {
+        cs->exception_index = RISCV_EXCP_INST_ACCESS_FAULT;
+        env->badaddr = addr;
+    } else if (is_write) {
+        cs->exception_index = RISCV_EXCP_STORE_AMO_ACCESS_FAULT;
+        env->badaddr = addr;
+    } else {
+        cs->exception_index = RISCV_EXCP_LOAD_ACCESS_FAULT;
+        env->badaddr = addr;
+    }
+    qemu_log_mask(LOG_GUEST_ERROR, "cpu_unassigned_access: %016" PRIx64 "\n",
+        addr);
+    do_raise_exception_err(env, cs->exception_index, env->pc);
+}
+
+#endif
+
+int riscv_cpu_handle_mmu_fault(CPUState *cs, vaddr address,
+        int access_type, int mmu_idx)
+{
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    CPURISCVState *env = &cpu->env;
+#if !defined(CONFIG_USER_ONLY)
+    hwaddr pa = 0;
+    int prot;
+#endif
+    int ret = TRANSLATE_FAIL;
+
+    qemu_log_mask(CPU_LOG_MMU,
+            "%s pc " TARGET_FMT_lx " ad %" VADDR_PRIx " access_type %d mmu_idx \
+             %d\n", __func__, env->pc, address, access_type, mmu_idx);
+
+#if !defined(CONFIG_USER_ONLY)
+    ret = get_physical_address(env, &pa, &prot, address, access_type,
+                               mmu_idx);
+    qemu_log_mask(CPU_LOG_MMU,
+            "%s address=%" VADDR_PRIx " ret %d physical " TARGET_FMT_plx
+             " prot %d\n", __func__, address, ret, pa, prot);
+    if (!pmp_hart_has_privs(env, pa, TARGET_PAGE_SIZE, 1 << access_type)) {
+        ret = TRANSLATE_FAIL;
+    }
+    if (ret == TRANSLATE_SUCCESS) {
+        tlb_set_page(cs, address & TARGET_PAGE_MASK, pa & TARGET_PAGE_MASK,
+                     prot, mmu_idx, TARGET_PAGE_SIZE);
+    } else if (ret == TRANSLATE_FAIL) {
+        raise_mmu_exception(env, address, access_type);
+    }
+#else
+    cs->exception_index = QEMU_USER_EXCP_FAULT;
+#endif
+    return ret;
+}
+
+/*
+ * Handle Traps
+ *
+ * Adapted from Spike's processor_t::take_trap.
+ *
+ */
+void riscv_cpu_do_interrupt(CPUState *cs)
+{
+#if !defined(CONFIG_USER_ONLY)
+
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    CPURISCVState *env = &cpu->env;
+
+    if (RISCV_DEBUG_INTERRUPT) {
+        int log_cause = cs->exception_index & RISCV_EXCP_INT_MASK;
+        if (cs->exception_index & RISCV_EXCP_INT_FLAG) {
+            qemu_log_mask(LOG_TRACE, "core   0: trap %s, epc 0x" TARGET_FMT_lx,
+                riscv_intr_names[log_cause], env->pc);
+        } else {
+            qemu_log_mask(LOG_TRACE, "core   0: intr %s, epc 0x" TARGET_FMT_lx,
+                riscv_excp_names[log_cause], env->pc);
+        }
+    }
+
+    target_ulong fixed_cause = 0;
+    if (cs->exception_index & (RISCV_EXCP_INT_FLAG)) {
+        /* hacky for now. the MSB (bit 63) indicates interrupt but cs->exception
+           index is only 32 bits wide */
+        fixed_cause = cs->exception_index & RISCV_EXCP_INT_MASK;
+        fixed_cause |= ((target_ulong)1) << (TARGET_LONG_BITS - 1);
+    } else {
+        /* fixup User ECALL -> correct priv ECALL */
+        if (cs->exception_index == RISCV_EXCP_U_ECALL) {
+            switch (env->priv) {
+            case PRV_U:
+                fixed_cause = RISCV_EXCP_U_ECALL;
+                break;
+            case PRV_S:
+                fixed_cause = RISCV_EXCP_S_ECALL;
+                break;
+            case PRV_H:
+                fixed_cause = RISCV_EXCP_H_ECALL;
+                break;
+            case PRV_M:
+                fixed_cause = RISCV_EXCP_M_ECALL;
+                break;
+            }
+        } else {
+            fixed_cause = cs->exception_index;
+        }
+    }
+
+    target_ulong backup_epc = env->pc;
+
+    target_ulong bit = fixed_cause;
+    target_ulong deleg = env->medeleg;
+
+    int hasbadaddr =
+        (fixed_cause == RISCV_EXCP_INST_ADDR_MIS) ||
+        (fixed_cause == RISCV_EXCP_INST_ACCESS_FAULT) ||
+        (fixed_cause == RISCV_EXCP_LOAD_ADDR_MIS) ||
+        (fixed_cause == RISCV_EXCP_STORE_AMO_ADDR_MIS) ||
+        (fixed_cause == RISCV_EXCP_LOAD_ACCESS_FAULT) ||
+        (fixed_cause == RISCV_EXCP_STORE_AMO_ACCESS_FAULT) ||
+        (fixed_cause == RISCV_EXCP_INST_PAGE_FAULT) ||
+        (fixed_cause == RISCV_EXCP_LOAD_PAGE_FAULT) ||
+        (fixed_cause == RISCV_EXCP_STORE_PAGE_FAULT);
+
+    if (bit & ((target_ulong)1 << (TARGET_LONG_BITS - 1))) {
+        deleg = env->mideleg;
+        bit &= ~((target_ulong)1 << (TARGET_LONG_BITS - 1));
+    }
+
+    if (env->priv <= PRV_S && bit < 64 && ((deleg >> bit) & 1)) {
+        /* handle the trap in S-mode */
+        /* No need to check STVEC for misaligned - lower 2 bits cannot be set */
+        env->pc = env->stvec;
+        env->scause = fixed_cause;
+        env->sepc = backup_epc;
+
+        if (hasbadaddr) {
+            if (RISCV_DEBUG_INTERRUPT) {
+                qemu_log_mask(LOG_TRACE, "core " TARGET_FMT_ld
+                    ": badaddr 0x" TARGET_FMT_lx, env->mhartid, env->badaddr);
+            }
+            env->sbadaddr = env->badaddr;
+        }
+
+        target_ulong s = env->mstatus;
+        s = set_field(s, MSTATUS_SPIE, get_field(s, MSTATUS_UIE << env->priv));
+        s = set_field(s, MSTATUS_SPP, env->priv);
+        s = set_field(s, MSTATUS_SIE, 0);
+        csr_write_helper(env, s, CSR_MSTATUS);
+        riscv_set_mode(env, PRV_S);
+    } else {
+        /* No need to check MTVEC for misaligned - lower 2 bits cannot be set */
+        env->pc = env->mtvec;
+        env->mepc = backup_epc;
+        env->mcause = fixed_cause;
+
+        if (hasbadaddr) {
+            if (RISCV_DEBUG_INTERRUPT) {
+                qemu_log_mask(LOG_TRACE, "core " TARGET_FMT_ld
+                    ": badaddr 0x" TARGET_FMT_lx, env->mhartid, env->badaddr);
+            }
+            env->mbadaddr = env->badaddr;
+        }
+
+        target_ulong s = env->mstatus;
+        s = set_field(s, MSTATUS_MPIE, get_field(s, MSTATUS_UIE << env->priv));
+        s = set_field(s, MSTATUS_MPP, env->priv);
+        s = set_field(s, MSTATUS_MIE, 0);
+        csr_write_helper(env, s, CSR_MSTATUS);
+        riscv_set_mode(env, PRV_M);
+    }
+    /* TODO yield load reservation  */
+#endif
+    cs->exception_index = EXCP_NONE; /* mark handled to qemu */
+}
diff --git a/target/riscv/helper.h b/target/riscv/helper.h
new file mode 100644
index 0000000..60f04a2
--- /dev/null
+++ b/target/riscv/helper.h
@@ -0,0 +1,78 @@ 
+/* Exceptions */
+DEF_HELPER_2(raise_exception, noreturn, env, i32)
+DEF_HELPER_1(raise_exception_debug, noreturn, env)
+DEF_HELPER_3(raise_exception_mbadaddr, noreturn, env, i32, tl)
+
+/* Floating Point - fused */
+DEF_HELPER_FLAGS_5(fmadd_s, TCG_CALL_NO_RWG, i64, env, i64, i64, i64, i64)
+DEF_HELPER_FLAGS_5(fmadd_d, TCG_CALL_NO_RWG, i64, env, i64, i64, i64, i64)
+DEF_HELPER_FLAGS_5(fmsub_s, TCG_CALL_NO_RWG, i64, env, i64, i64, i64, i64)
+DEF_HELPER_FLAGS_5(fmsub_d, TCG_CALL_NO_RWG, i64, env, i64, i64, i64, i64)
+DEF_HELPER_FLAGS_5(fnmsub_s, TCG_CALL_NO_RWG, i64, env, i64, i64, i64, i64)
+DEF_HELPER_FLAGS_5(fnmsub_d, TCG_CALL_NO_RWG, i64, env, i64, i64, i64, i64)
+DEF_HELPER_FLAGS_5(fnmadd_s, TCG_CALL_NO_RWG, i64, env, i64, i64, i64, i64)
+DEF_HELPER_FLAGS_5(fnmadd_d, TCG_CALL_NO_RWG, i64, env, i64, i64, i64, i64)
+
+/* Floating Point - Single Precision */
+DEF_HELPER_FLAGS_4(fadd_s, TCG_CALL_NO_RWG, i64, env, i64, i64, i64)
+DEF_HELPER_FLAGS_4(fsub_s, TCG_CALL_NO_RWG, i64, env, i64, i64, i64)
+DEF_HELPER_FLAGS_4(fmul_s, TCG_CALL_NO_RWG, i64, env, i64, i64, i64)
+DEF_HELPER_FLAGS_4(fdiv_s, TCG_CALL_NO_RWG, i64, env, i64, i64, i64)
+DEF_HELPER_FLAGS_3(fmin_s, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fmax_s, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fsqrt_s, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fle_s, TCG_CALL_NO_RWG, tl, env, i64, i64)
+DEF_HELPER_FLAGS_3(flt_s, TCG_CALL_NO_RWG, tl, env, i64, i64)
+DEF_HELPER_FLAGS_3(feq_s, TCG_CALL_NO_RWG, tl, env, i64, i64)
+DEF_HELPER_FLAGS_3(fcvt_w_s, TCG_CALL_NO_RWG, tl, env, i64, i64)
+DEF_HELPER_FLAGS_3(fcvt_wu_s, TCG_CALL_NO_RWG, tl, env, i64, i64)
+#if defined(TARGET_RISCV64)
+DEF_HELPER_FLAGS_3(fcvt_l_s, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fcvt_lu_s, TCG_CALL_NO_RWG, i64, env, i64, i64)
+#endif
+DEF_HELPER_FLAGS_3(fcvt_s_w, TCG_CALL_NO_RWG, i64, env, tl, i64)
+DEF_HELPER_FLAGS_3(fcvt_s_wu, TCG_CALL_NO_RWG, i64, env, tl, i64)
+#if defined(TARGET_RISCV64)
+DEF_HELPER_FLAGS_3(fcvt_s_l, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fcvt_s_lu, TCG_CALL_NO_RWG, i64, env, i64, i64)
+#endif
+DEF_HELPER_FLAGS_2(fclass_s, TCG_CALL_NO_RWG, tl, env, i64)
+
+/* Floating Point - Double Precision */
+DEF_HELPER_FLAGS_4(fadd_d, TCG_CALL_NO_RWG, i64, env, i64, i64, i64)
+DEF_HELPER_FLAGS_4(fsub_d, TCG_CALL_NO_RWG, i64, env, i64, i64, i64)
+DEF_HELPER_FLAGS_4(fmul_d, TCG_CALL_NO_RWG, i64, env, i64, i64, i64)
+DEF_HELPER_FLAGS_4(fdiv_d, TCG_CALL_NO_RWG, i64, env, i64, i64, i64)
+DEF_HELPER_FLAGS_3(fmin_d, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fmax_d, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fcvt_s_d, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fcvt_d_s, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fsqrt_d, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fle_d, TCG_CALL_NO_RWG, tl, env, i64, i64)
+DEF_HELPER_FLAGS_3(flt_d, TCG_CALL_NO_RWG, tl, env, i64, i64)
+DEF_HELPER_FLAGS_3(feq_d, TCG_CALL_NO_RWG, tl, env, i64, i64)
+DEF_HELPER_FLAGS_3(fcvt_w_d, TCG_CALL_NO_RWG, tl, env, i64, i64)
+DEF_HELPER_FLAGS_3(fcvt_wu_d, TCG_CALL_NO_RWG, tl, env, i64, i64)
+#if defined(TARGET_RISCV64)
+DEF_HELPER_FLAGS_3(fcvt_l_d, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fcvt_lu_d, TCG_CALL_NO_RWG, i64, env, i64, i64)
+#endif
+DEF_HELPER_FLAGS_3(fcvt_d_w, TCG_CALL_NO_RWG, i64, env, tl, i64)
+DEF_HELPER_FLAGS_3(fcvt_d_wu, TCG_CALL_NO_RWG, i64, env, tl, i64)
+#if defined(TARGET_RISCV64)
+DEF_HELPER_FLAGS_3(fcvt_d_l, TCG_CALL_NO_RWG, i64, env, i64, i64)
+DEF_HELPER_FLAGS_3(fcvt_d_lu, TCG_CALL_NO_RWG, i64, env, i64, i64)
+#endif
+DEF_HELPER_FLAGS_2(fclass_d, TCG_CALL_NO_RWG, tl, env, i64)
+
+/* Special functions */
+DEF_HELPER_3(csrrw, tl, env, tl, tl)
+DEF_HELPER_4(csrrs, tl, env, tl, tl, tl)
+DEF_HELPER_4(csrrc, tl, env, tl, tl, tl)
+#ifndef CONFIG_USER_ONLY
+DEF_HELPER_2(sret, tl, env, tl)
+DEF_HELPER_2(mret, tl, env, tl)
+DEF_HELPER_1(wfi, void, env)
+DEF_HELPER_1(tlb_flush, void, env)
+DEF_HELPER_1(fence_i, void, env)
+#endif
diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
new file mode 100644
index 0000000..1930ab1
--- /dev/null
+++ b/target/riscv/op_helper.c
@@ -0,0 +1,682 @@ 
+/*
+ * RISC-V Emulation Helpers for QEMU.
+ *
+ * Author: Sagar Karandikar, sagark@eecs.berkeley.edu
+ *
+ *
+ * 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 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 "qemu/log.h"
+#include "cpu.h"
+#include "qemu/main-loop.h"
+#include "exec/exec-all.h"
+#include "exec/helper-proto.h"
+
+#ifndef CONFIG_USER_ONLY
+
+#if defined(TARGET_RISCV32)
+static const char valid_vm_1_09[16] = {
+    [VM_1_09_MBARE] = 1,
+    [VM_1_09_SV32] = 1,
+};
+static const char valid_vm_1_10[16] = {
+    [VM_1_10_MBARE] = 1,
+    [VM_1_10_SV32] = 1
+};
+#elif defined(TARGET_RISCV64)
+static const char valid_vm_1_09[16] = {
+    [VM_1_09_MBARE] = 1,
+    [VM_1_09_SV39] = 1,
+    [VM_1_09_SV48] = 1,
+};
+static const char valid_vm_1_10[16] = {
+    [VM_1_10_MBARE] = 1,
+    [VM_1_10_SV39] = 1,
+    [VM_1_10_SV48] = 1,
+    [VM_1_10_SV57] = 1
+};
+#endif
+
+static int validate_vm(CPURISCVState *env, target_ulong vm)
+{
+    return (env->priv_ver >= PRIV_VERSION_1_10_0) ?
+        valid_vm_1_10[vm & 0xf] : valid_vm_1_09[vm & 0xf];
+}
+
+#endif
+
+/* Exceptions processing helpers */
+inline void QEMU_NORETURN do_raise_exception_err(CPURISCVState *env,
+                                          uint32_t exception, uintptr_t pc)
+{
+    CPUState *cs = CPU(riscv_env_get_cpu(env));
+    qemu_log_mask(CPU_LOG_INT, "%s: %d\n", __func__, exception);
+    cs->exception_index = exception;
+    cpu_loop_exit_restore(cs, pc);
+}
+
+void helper_raise_exception(CPURISCVState *env, uint32_t exception)
+{
+    do_raise_exception_err(env, exception, 0);
+}
+
+void helper_raise_exception_debug(CPURISCVState *env)
+{
+    do_raise_exception_err(env, EXCP_DEBUG, 0);
+}
+
+void helper_raise_exception_mbadaddr(CPURISCVState *env, uint32_t exception,
+        target_ulong bad_pc) {
+    env->badaddr = bad_pc;
+    do_raise_exception_err(env, exception, 0);
+}
+
+/*
+ * Handle writes to CSRs and any resulting special behavior
+ *
+ * Adapted from Spike's processor_t::set_csr
+ */
+inline void csr_write_helper(CPURISCVState *env, target_ulong val_to_write,
+        target_ulong csrno)
+{
+    #ifdef RISCV_DEBUG_PRINT
+    qemu_log_mask(LOG_TRACE, "Write CSR reg: 0x" TARGET_FMT_lx, csrno);
+    qemu_log_mask(LOG_TRACE, "Write CSR val: 0x" TARGET_FMT_lx, val_to_write);
+    #endif
+
+#ifndef CONFIG_USER_ONLY
+    uint64_t delegable_ints = MIP_SSIP | MIP_STIP | MIP_SEIP | (1 << IRQ_X_COP);
+    uint64_t all_ints = delegable_ints | MIP_MSIP | MIP_MTIP;
+#endif
+
+    switch (csrno) {
+    case CSR_FFLAGS:
+        if (riscv_mstatus_fs(env)) {
+            env->fflags = val_to_write & (FSR_AEXC >> FSR_AEXC_SHIFT);
+        } else {
+            helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        }
+        break;
+    case CSR_FRM:
+        if (riscv_mstatus_fs(env)) {
+            env->frm = val_to_write & (FSR_RD >> FSR_RD_SHIFT);
+        } else {
+            helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        }
+        break;
+    case CSR_FCSR:
+        if (riscv_mstatus_fs(env)) {
+            env->fflags = (val_to_write & FSR_AEXC) >> FSR_AEXC_SHIFT;
+            env->frm = (val_to_write & FSR_RD) >> FSR_RD_SHIFT;
+        } else {
+            helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        }
+        break;
+#ifndef CONFIG_USER_ONLY
+    case CSR_MSTATUS: {
+        target_ulong mstatus = env->mstatus;
+        target_ulong mask = 0;
+        if (env->priv_ver <= PRIV_VERSION_1_09_1) {
+            if ((val_to_write ^ mstatus) & (MSTATUS_MXR | MSTATUS_MPP |
+                    MSTATUS_MPRV | MSTATUS_SUM | MSTATUS_VM)) {
+                helper_tlb_flush(env);
+            }
+            mask = MSTATUS_SIE | MSTATUS_SPIE | MSTATUS_MIE | MSTATUS_MPIE |
+                MSTATUS_SPP | MSTATUS_FS | MSTATUS_MPRV | MSTATUS_SUM |
+                MSTATUS_MPP | MSTATUS_MXR |
+                (validate_vm(env, get_field(val_to_write, MSTATUS_VM)) ?
+                    MSTATUS_VM : 0);
+        }
+        if (env->priv_ver >= PRIV_VERSION_1_10_0) {
+            if ((val_to_write ^ mstatus) & (MSTATUS_MXR | MSTATUS_MPP |
+                    MSTATUS_MPRV | MSTATUS_SUM)) {
+                helper_tlb_flush(env);
+            }
+            mask = MSTATUS_SIE | MSTATUS_SPIE | MSTATUS_MIE | MSTATUS_MPIE |
+                MSTATUS_SPP | MSTATUS_FS | MSTATUS_MPRV | MSTATUS_SUM |
+                MSTATUS_MPP | MSTATUS_MXR;
+        }
+        mstatus = (mstatus & ~mask) | (val_to_write & mask);
+        int dirty = (mstatus & MSTATUS_FS) == MSTATUS_FS;
+        dirty |= (mstatus & MSTATUS_XS) == MSTATUS_XS;
+        mstatus = set_field(mstatus, MSTATUS_SD, dirty);
+        env->mstatus = mstatus;
+        break;
+    }
+    case CSR_MIP: {
+        target_ulong mask = MIP_SSIP | MIP_STIP | MIP_SEIP;
+        env->mip = (env->mip & ~mask) |
+            (val_to_write & mask);
+        qemu_mutex_lock_iothread();
+        if (env->mip & MIP_SSIP) {
+            qemu_irq_raise(SSIP_IRQ);
+        } else {
+            qemu_irq_lower(SSIP_IRQ);
+        }
+        if (env->mip & MIP_STIP) {
+            qemu_irq_raise(STIP_IRQ);
+        } else {
+            qemu_irq_lower(STIP_IRQ);
+        }
+        if (env->mip & MIP_SEIP) {
+            qemu_irq_raise(SEIP_IRQ);
+        } else {
+            qemu_irq_lower(SEIP_IRQ);
+        }
+        qemu_mutex_unlock_iothread();
+        break;
+    }
+    case CSR_MIE: {
+        env->mie = (env->mie & ~all_ints) |
+            (val_to_write & all_ints);
+        break;
+    }
+    case CSR_MIDELEG:
+        env->mideleg = (env->mideleg & ~delegable_ints)
+                                | (val_to_write & delegable_ints);
+        break;
+    case CSR_MEDELEG: {
+        target_ulong mask = 0;
+        mask |= 1ULL << (RISCV_EXCP_INST_ADDR_MIS);
+        mask |= 1ULL << (RISCV_EXCP_INST_ACCESS_FAULT);
+        mask |= 1ULL << (RISCV_EXCP_ILLEGAL_INST);
+        mask |= 1ULL << (RISCV_EXCP_BREAKPOINT);
+        mask |= 1ULL << (RISCV_EXCP_LOAD_ADDR_MIS);
+        mask |= 1ULL << (RISCV_EXCP_LOAD_ACCESS_FAULT);
+        mask |= 1ULL << (RISCV_EXCP_STORE_AMO_ADDR_MIS);
+        mask |= 1ULL << (RISCV_EXCP_STORE_AMO_ACCESS_FAULT);
+        mask |= 1ULL << (RISCV_EXCP_U_ECALL);
+        mask |= 1ULL << (RISCV_EXCP_S_ECALL);
+        mask |= 1ULL << (RISCV_EXCP_H_ECALL);
+        mask |= 1ULL << (RISCV_EXCP_M_ECALL);
+        mask |= 1ULL << (RISCV_EXCP_INST_PAGE_FAULT);
+        mask |= 1ULL << (RISCV_EXCP_LOAD_PAGE_FAULT);
+        mask |= 1ULL << (RISCV_EXCP_STORE_PAGE_FAULT);
+        env->medeleg = (env->medeleg & ~mask)
+                                | (val_to_write & mask);
+        break;
+    }
+    case CSR_MINSTRET:
+        qemu_log_mask(LOG_UNIMP, "CSR_MINSTRET: write not implemented");
+        helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        break;
+    case CSR_MCYCLE:
+        qemu_log_mask(LOG_UNIMP, "CSR_MCYCLE: write not implemented");
+        helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        break;
+    case CSR_MINSTRETH:
+        qemu_log_mask(LOG_UNIMP, "CSR_MINSTRETH: write not implemented");
+        helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        break;
+    case CSR_MCYCLEH:
+        qemu_log_mask(LOG_UNIMP, "CSR_MCYCLEH: write not implemented");
+        helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        break;
+    case CSR_MUCOUNTEREN:
+        env->mucounteren = val_to_write;
+        break;
+    case CSR_MSCOUNTEREN:
+        env->mscounteren = val_to_write;
+        break;
+    case CSR_SSTATUS: {
+        target_ulong ms = env->mstatus;
+        target_ulong mask = SSTATUS_SIE | SSTATUS_SPIE | SSTATUS_UIE
+            | SSTATUS_UPIE | SSTATUS_SPP | SSTATUS_FS | SSTATUS_XS
+            | SSTATUS_SUM | SSTATUS_MXR | SSTATUS_SD;
+        ms = (ms & ~mask) | (val_to_write & mask);
+        csr_write_helper(env, ms, CSR_MSTATUS);
+        break;
+    }
+    case CSR_SIP: {
+        target_ulong next_mip = (env->mip & ~env->mideleg)
+                                | (val_to_write & env->mideleg);
+        csr_write_helper(env, next_mip, CSR_MIP);
+        break;
+    }
+    case CSR_SIE: {
+        target_ulong next_mie = (env->mie & ~env->mideleg)
+                                | (val_to_write & env->mideleg);
+        csr_write_helper(env, next_mie, CSR_MIE);
+        break;
+    }
+    case CSR_SATP: /* CSR_SPTBR */ {
+        if (env->priv_ver <= PRIV_VERSION_1_09_1 && (val_to_write ^ env->sptbr))
+        {
+            helper_tlb_flush(env);
+            env->sptbr = val_to_write & (((target_ulong)
+                1 << (TARGET_PHYS_ADDR_SPACE_BITS - PGSHIFT)) - 1);
+        }
+        if (env->priv_ver >= PRIV_VERSION_1_10_0 &&
+            validate_vm(env, get_field(val_to_write, SATP_MODE)) &&
+            ((val_to_write ^ env->satp) & (SATP_MODE | SATP_ASID | SATP_PPN)))
+        {
+            helper_tlb_flush(env);
+            env->satp = val_to_write;
+        }
+        break;
+    }
+    case CSR_SEPC:
+        env->sepc = val_to_write;
+        break;
+    case CSR_STVEC:
+        if (val_to_write & 1) {
+            qemu_log_mask(LOG_UNIMP, "CSR_STVEC: vectored traps not supported");
+            helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        } else {
+            env->stvec = val_to_write >> 2 << 2;
+        }
+        break;
+    case CSR_SCOUNTEREN:
+        env->scounteren = val_to_write;
+        break;
+    case CSR_SSCRATCH:
+        env->sscratch = val_to_write;
+        break;
+    case CSR_SCAUSE:
+        env->scause = val_to_write;
+        break;
+    case CSR_SBADADDR:
+        env->sbadaddr = val_to_write;
+        break;
+    case CSR_MEPC:
+        env->mepc = val_to_write;
+        break;
+    case CSR_MTVEC:
+        if (val_to_write & 1) {
+            qemu_log_mask(LOG_UNIMP, "CSR_MTVEC: vectored traps not supported");
+            helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        } else {
+            env->mtvec = val_to_write >> 2 << 2;
+        }
+        break;
+    case CSR_MCOUNTEREN:
+        env->mcounteren = val_to_write;
+        break;
+    case CSR_MSCRATCH:
+        env->mscratch = val_to_write;
+        break;
+    case CSR_MCAUSE:
+        env->mcause = val_to_write;
+        break;
+    case CSR_MBADADDR:
+        env->mbadaddr = val_to_write;
+        break;
+    case CSR_MISA: {
+        if (!(val_to_write & (1L << ('F' - 'A')))) {
+            val_to_write &= ~(1L << ('D' - 'A'));
+        }
+
+        /* allow MAFDC bits in MISA to be modified */
+        target_ulong mask = 0;
+        mask |= 1L << ('M' - 'A');
+        mask |= 1L << ('A' - 'A');
+        mask |= 1L << ('F' - 'A');
+        mask |= 1L << ('D' - 'A');
+        mask |= 1L << ('C' - 'A');
+        mask &= env->misa_mask;
+
+        env->misa = (val_to_write & mask) | (env->misa & ~mask);
+        break;
+    }
+    case CSR_PMPCFG0:
+    case CSR_PMPCFG1:
+    case CSR_PMPCFG2:
+    case CSR_PMPCFG3:
+       pmpcfg_csr_write(env, csrno - CSR_PMPCFG0, val_to_write);
+       break;
+    case CSR_PMPADDR0:
+    case CSR_PMPADDR1:
+    case CSR_PMPADDR2:
+    case CSR_PMPADDR3:
+    case CSR_PMPADDR4:
+    case CSR_PMPADDR5:
+    case CSR_PMPADDR6:
+    case CSR_PMPADDR7:
+    case CSR_PMPADDR8:
+    case CSR_PMPADDR9:
+    case CSR_PMPADDR10:
+    case CSR_PMPADDR11:
+    case CSR_PMPADDR12:
+    case CSR_PMPADDR13:
+    case CSR_PMPADDR14:
+    case CSR_PMPADDR15:
+       pmpaddr_csr_write(env, csrno - CSR_PMPADDR0, val_to_write);
+       break;
+#endif
+    default:
+        helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+    }
+}
+
+/*
+ * Handle reads to CSRs and any resulting special behavior
+ *
+ * Adapted from Spike's processor_t::get_csr
+ */
+inline target_ulong csr_read_helper(CPURISCVState *env, target_ulong csrno)
+{
+    #ifdef RISCV_DEBUG_PRINT
+    qemu_log_mask(LOG_TRACE, "Read CSR reg: 0x" TARGET_FMT_lx, csrno);
+    #endif
+
+#ifndef CONFIG_USER_ONLY
+    target_ulong ctr_en = env->priv == PRV_U ? env->mucounteren :
+                   env->priv == PRV_S ? env->mscounteren : -1U;
+#else
+    target_ulong ctr_en = env->mucounteren;
+#endif
+    target_ulong ctr_ok = (ctr_en >> (csrno & 31)) & 1;
+
+    if (ctr_ok) {
+        if (csrno >= CSR_HPMCOUNTER3 && csrno <= CSR_HPMCOUNTER31) {
+            return 0;
+        }
+#if defined(TARGET_RISCV32)
+        if (csrno >= CSR_HPMCOUNTER3H && csrno <= CSR_HPMCOUNTER31H) {
+            return 0;
+        }
+#endif
+    }
+    if (csrno >= CSR_MHPMCOUNTER3 && csrno <= CSR_MHPMCOUNTER31) {
+        return 0;
+    }
+#if defined(TARGET_RISCV32)
+    if (csrno >= CSR_MHPMCOUNTER3 && csrno <= CSR_MHPMCOUNTER31) {
+        return 0;
+    }
+#endif
+    if (csrno >= CSR_MHPMEVENT3 && csrno <= CSR_MHPMEVENT31) {
+        return 0;
+    }
+
+    switch (csrno) {
+    case CSR_FFLAGS:
+        if (riscv_mstatus_fs(env)) {
+            return env->fflags;
+        } else {
+            helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        }
+    case CSR_FRM:
+        if (riscv_mstatus_fs(env)) {
+            return env->frm;
+        } else {
+            helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        }
+    case CSR_FCSR:
+        if (riscv_mstatus_fs(env)) {
+            return env->fflags << FSR_AEXC_SHIFT | env->frm << FSR_RD_SHIFT;
+        } else {
+            helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+        }
+#ifdef CONFIG_USER_ONLY
+    case CSR_TIME:
+    case CSR_CYCLE:
+    case CSR_INSTRET:
+        return (target_ulong)cpu_get_host_ticks();
+    case CSR_TIMEH:
+    case CSR_CYCLEH:
+    case CSR_INSTRETH:
+#if defined(TARGET_RISCV32)
+        return (target_ulong)(cpu_get_host_ticks() >> 32);
+#endif
+        break;
+#endif
+#ifndef CONFIG_USER_ONLY
+    case CSR_TIME:
+        return cpu_riscv_read_rtc();
+    case CSR_TIMEH:
+        return (target_ulong)(cpu_riscv_read_rtc() >> 32);
+    case CSR_INSTRET:
+    case CSR_CYCLE:
+        if (ctr_ok) {
+            return cpu_riscv_read_instret(env);
+        }
+        break;
+    case CSR_MINSTRET:
+    case CSR_MCYCLE:
+        return cpu_riscv_read_instret(env);
+    case CSR_MINSTRETH:
+    case CSR_MCYCLEH:
+#if defined(TARGET_RISCV32)
+        return cpu_riscv_read_instret(env) >> 32;
+#endif
+        break;
+    case CSR_MUCOUNTEREN:
+        return env->mucounteren;
+    case CSR_MSCOUNTEREN:
+        return env->mscounteren;
+    case CSR_SSTATUS: {
+        target_ulong mask = SSTATUS_SIE | SSTATUS_SPIE | SSTATUS_UIE
+            | SSTATUS_UPIE | SSTATUS_SPP | SSTATUS_FS | SSTATUS_XS
+            | SSTATUS_SUM |  SSTATUS_SD;
+        if (env->priv_ver >= PRIV_VERSION_1_10_0) {
+            mask |= SSTATUS_MXR;
+        }
+        return env->mstatus & mask;
+    }
+    case CSR_SIP:
+        return env->mip & env->mideleg;
+    case CSR_SIE:
+        return env->mie & env->mideleg;
+    case CSR_SEPC:
+        return env->sepc;
+    case CSR_SBADADDR:
+        return env->sbadaddr;
+    case CSR_STVEC:
+        return env->stvec;
+    case CSR_SCOUNTEREN:
+        return env->scounteren;
+    case CSR_SCAUSE:
+        return env->scause;
+    case CSR_SPTBR:
+        if (env->priv_ver >= PRIV_VERSION_1_10_0) {
+            return env->satp;
+        } else {
+            return env->sptbr;
+        }
+    case CSR_SSCRATCH:
+        return env->sscratch;
+    case CSR_MSTATUS:
+        return env->mstatus;
+    case CSR_MIP:
+        return env->mip;
+    case CSR_MIE:
+        return env->mie;
+    case CSR_MEPC:
+        return env->mepc;
+    case CSR_MSCRATCH:
+        return env->mscratch;
+    case CSR_MCAUSE:
+        return env->mcause;
+    case CSR_MBADADDR:
+        return env->mbadaddr;
+    case CSR_MISA:
+        return env->misa;
+    case CSR_MARCHID:
+        return 0; /* as spike does */
+    case CSR_MIMPID:
+        return 0; /* as spike does */
+    case CSR_MVENDORID:
+        return 0; /* as spike does */
+    case CSR_MHARTID:
+        return env->mhartid;
+    case CSR_MTVEC:
+        return env->mtvec;
+    case CSR_MCOUNTEREN:
+        return env->mcounteren;
+    case CSR_MEDELEG:
+        return env->medeleg;
+    case CSR_MIDELEG:
+        return env->mideleg;
+    case CSR_PMPCFG0:
+    case CSR_PMPCFG1:
+    case CSR_PMPCFG2:
+    case CSR_PMPCFG3:
+       return pmpcfg_csr_read(env, csrno - CSR_PMPCFG0);
+    case CSR_PMPADDR0:
+    case CSR_PMPADDR1:
+    case CSR_PMPADDR2:
+    case CSR_PMPADDR3:
+    case CSR_PMPADDR4:
+    case CSR_PMPADDR5:
+    case CSR_PMPADDR6:
+    case CSR_PMPADDR7:
+    case CSR_PMPADDR8:
+    case CSR_PMPADDR9:
+    case CSR_PMPADDR10:
+    case CSR_PMPADDR11:
+    case CSR_PMPADDR12:
+    case CSR_PMPADDR13:
+    case CSR_PMPADDR14:
+    case CSR_PMPADDR15:
+       return pmpaddr_csr_read(env, csrno - CSR_PMPADDR0);
+#endif
+    }
+    /* used by e.g. MTIME read */
+    helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+    return 0;
+}
+
+/*
+ * Check that CSR access is allowed.
+ *
+ * Adapted from Spike's decode.h:validate_csr
+ */
+void validate_csr(CPURISCVState *env, uint64_t which, uint64_t write)
+{
+#ifndef CONFIG_USER_ONLY
+    unsigned csr_priv = get_field((which), 0x300);
+    unsigned csr_read_only = get_field((which), 0xC00) == 3;
+    if (((write) && csr_read_only) || (env->priv < csr_priv)) {
+        do_raise_exception_err(env, RISCV_EXCP_ILLEGAL_INST, env->pc);
+    }
+#endif
+}
+
+target_ulong helper_csrrw(CPURISCVState *env, target_ulong src,
+        target_ulong csr)
+{
+    validate_csr(env, csr, 1);
+    uint64_t csr_backup = csr_read_helper(env, csr);
+    csr_write_helper(env, src, csr);
+    return csr_backup;
+}
+
+target_ulong helper_csrrs(CPURISCVState *env, target_ulong src,
+        target_ulong csr, target_ulong rs1_pass)
+{
+    validate_csr(env, csr, rs1_pass != 0);
+    uint64_t csr_backup = csr_read_helper(env, csr);
+    if (rs1_pass != 0) {
+        csr_write_helper(env, src | csr_backup, csr);
+    }
+    return csr_backup;
+}
+
+target_ulong helper_csrrc(CPURISCVState *env, target_ulong src,
+        target_ulong csr, target_ulong rs1_pass)
+{
+    validate_csr(env, csr, rs1_pass != 0);
+    uint64_t csr_backup = csr_read_helper(env, csr);
+    if (rs1_pass != 0) {
+        csr_write_helper(env, (~src) & csr_backup, csr);
+    }
+    return csr_backup;
+}
+
+#ifndef CONFIG_USER_ONLY
+
+void riscv_set_mode(CPURISCVState *env, target_ulong newpriv)
+{
+    if (newpriv > PRV_M) {
+        g_assert_not_reached();
+    }
+    if (newpriv == PRV_H) {
+        newpriv = PRV_U;
+    }
+    helper_tlb_flush(env);
+    env->priv = newpriv;
+}
+
+target_ulong helper_sret(CPURISCVState *env, target_ulong cpu_pc_deb)
+{
+    if (!(env->priv >= PRV_S)) {
+        helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+    }
+
+    target_ulong retpc = env->sepc;
+    if (!riscv_has_ext(env, RVC) && (retpc & 0x3)) {
+        helper_raise_exception(env, RISCV_EXCP_INST_ADDR_MIS);
+    }
+
+    target_ulong mstatus = env->mstatus;
+    target_ulong prev_priv = get_field(mstatus, MSTATUS_SPP);
+    mstatus = set_field(mstatus, MSTATUS_UIE << prev_priv,
+                        get_field(mstatus, MSTATUS_SPIE));
+    mstatus = set_field(mstatus, MSTATUS_SPIE, 0);
+    mstatus = set_field(mstatus, MSTATUS_SPP, PRV_U);
+    riscv_set_mode(env, prev_priv);
+    csr_write_helper(env, mstatus, CSR_MSTATUS);
+
+    return retpc;
+}
+
+target_ulong helper_mret(CPURISCVState *env, target_ulong cpu_pc_deb)
+{
+    if (!(env->priv >= PRV_M)) {
+        helper_raise_exception(env, RISCV_EXCP_ILLEGAL_INST);
+    }
+
+    target_ulong retpc = env->mepc;
+    if (!riscv_has_ext(env, RVC) && (retpc & 0x3)) {
+        helper_raise_exception(env, RISCV_EXCP_INST_ADDR_MIS);
+    }
+
+    target_ulong mstatus = env->mstatus;
+    target_ulong prev_priv = get_field(mstatus, MSTATUS_MPP);
+    mstatus = set_field(mstatus, MSTATUS_UIE << prev_priv,
+                        get_field(mstatus, MSTATUS_MPIE));
+    mstatus = set_field(mstatus, MSTATUS_MPIE, 0);
+    mstatus = set_field(mstatus, MSTATUS_MPP, PRV_U);
+    riscv_set_mode(env, prev_priv);
+    csr_write_helper(env, mstatus, CSR_MSTATUS);
+
+    return retpc;
+}
+
+
+void helper_wfi(CPURISCVState *env)
+{
+    CPUState *cs = CPU(riscv_env_get_cpu(env));
+
+    cs->halted = 1;
+    cs->exception_index = EXCP_HLT;
+    cpu_loop_exit(cs);
+}
+
+void helper_fence_i(CPURISCVState *env)
+{
+    /* FENCE.I is a no-op in qemu as self modifying code is detected */
+}
+
+void helper_tlb_flush(CPURISCVState *env)
+{
+    RISCVCPU *cpu = riscv_env_get_cpu(env);
+    CPUState *cs = CPU(cpu);
+    tlb_flush(cs);
+}
+
+#endif /* !CONFIG_USER_ONLY */