On 9/7/2026 1:39 AM, Alistair Francis wrote:
On Mon, 2026-08-31 at 11:10 -0300, Daniel Henrique Barboza wrote:
From: Chao Liu <[email protected]>

RISC-V Debug Specification:
https://github.com/riscv/riscv-debug-spec/releases/tag/1.0

Add architectural state for Sdext Debug Mode: debug_mode, dcsr, dpc
and dscratch0/1. Wire up CSR access for dcsr/dpc/dscratch and gate
them to Debug Mode (or host debugger access).

The Sdext is not fully implemented, so it is disabled by default.

Signed-off-by: Chao Liu <[email protected]>
Reviewed-by: Daniel Henrique Barboza
<[email protected]>
Tested-by: Tao Tang <[email protected]>

You are missing your Signed-off-by line here (and on the other
patches).

Ops. I'll re-send it with my s-o-b on patches 1-6.


Thanks,
Daniel


---
  target/riscv/cpu.c                |   7 ++
  target/riscv/cpu.h                |   4 +
  target/riscv/cpu_bits.h           |  33 ++++++++
  target/riscv/cpu_cfg_fields.h.inc |   1 +
  target/riscv/machine.c            |  20 +++++
  target/riscv/tcg/csr.c            | 126
++++++++++++++++++++++++++++++
  6 files changed, 191 insertions(+)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 61109672d6..c2078473aa 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -248,6 +248,7 @@ const RISCVIsaExtData isa_edata_arr[] = {
      ISA_EXT_DATA_ENTRY(zvkt, PRIV_VERSION_1_12_0, ext_zvkt),
      ISA_EXT_DATA_ENTRY(zhinx, PRIV_VERSION_1_12_0, ext_zhinx),
      ISA_EXT_DATA_ENTRY(zhinxmin, PRIV_VERSION_1_12_0, ext_zhinxmin),
+    ISA_EXT_DATA_ENTRY(sdext, PRIV_VERSION_1_12_0, ext_sdext),
      ISA_EXT_DATA_ENTRY(sdtrig, PRIV_VERSION_1_12_0, ext_sdtrig),
      ISA_INTERNAL_EXT_DATA_ENTRY(shcounterenw, PRIV_VERSION_1_12_0,
                                  has_priv_1_12),
@@ -1091,6 +1092,12 @@ static void riscv_cpu_reset_hold(Object *obj,
ResetType type)
 #ifndef CONFIG_USER_ONLY
  #ifdef CONFIG_TCG
+    env->debug_mode = false;
+    env->dcsr = DCSR_DEBUGVER(4);
+    env->dpc = 0;
+    env->dscratch[0] = 0;
+    env->dscratch[1] = 0;
+
      if (cpu->cfg.debug || cpu->cfg.ext_sdtrig) {
          riscv_trigger_reset_hold(env);
      }
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 718b66487a..74bddc8415 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -507,6 +507,10 @@ struct CPUArchState {
     /* True if in debugger mode.  */
      bool debugger;
+    bool debug_mode;
+    target_ulong dcsr;
+    target_ulong dpc;
+    target_ulong dscratch[2];
     uint64_t mstateen[SMSTATEEN_MAX_COUNT];
      uint64_t hstateen[SMSTATEEN_MAX_COUNT];
diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
index c01050ce2b..769c945517 100644
--- a/target/riscv/cpu_bits.h
+++ b/target/riscv/cpu_bits.h
@@ -467,6 +467,39 @@
  #define CSR_DCSR            0x7b0
  #define CSR_DPC             0x7b1
  #define CSR_DSCRATCH        0x7b2
+#define CSR_DSCRATCH1       0x7b3
+
+/* DCSR fields */
+#define DCSR_XDEBUGVER_SHIFT    28
+#define DCSR_XDEBUGVER_MASK     (0xfu << DCSR_XDEBUGVER_SHIFT)
+#define DCSR_DEBUGVER(val)      ((target_ulong)(val) <<
DCSR_XDEBUGVER_SHIFT)
+#define DCSR_EXTCAUSE_SHIFT     24
+#define DCSR_EXTCAUSE_MASK      (0x7u << DCSR_EXTCAUSE_SHIFT)
+#define DCSR_CETRIG             BIT(19)
+#define DCSR_PELP               BIT(18)
+#define DCSR_EBREAKVS           BIT(17)
+#define DCSR_EBREAKVU           BIT(16)
+#define DCSR_EBREAKM            BIT(15)
+#define DCSR_EBREAKS            BIT(13)
+#define DCSR_EBREAKU            BIT(12)
+#define DCSR_STEPIE             BIT(11)
+#define DCSR_STOPCOUNT          BIT(10)
+#define DCSR_STOPTIME           BIT(9)
+#define DCSR_CAUSE_SHIFT        6
+#define DCSR_CAUSE_MASK         (0x7u << DCSR_CAUSE_SHIFT)
+#define DCSR_V                  BIT(5)
+#define DCSR_MPRVEN             BIT(4)
+#define DCSR_NMIP               BIT(3)
+#define DCSR_STEP               BIT(2)
+#define DCSR_PRV_MASK           0x3u
+
+#define DCSR_CAUSE_EBREAK       1
+#define DCSR_CAUSE_TRIGGER      2
+#define DCSR_CAUSE_HALTREQ      3
+#define DCSR_CAUSE_STEP         4
+#define DCSR_CAUSE_RESET        5
+#define DCSR_CAUSE_GROUP        6
+#define DCSR_CAUSE_OTHER        7
 /* Performance Counters */
  #define CSR_MHPMCOUNTER3    0xb03
diff --git a/target/riscv/cpu_cfg_fields.h.inc
b/target/riscv/cpu_cfg_fields.h.inc
index f91c780299..24f3606f94 100644
--- a/target/riscv/cpu_cfg_fields.h.inc
+++ b/target/riscv/cpu_cfg_fields.h.inc
@@ -105,6 +105,7 @@ BOOL_FIELD(ext_zvfbfmin)
  BOOL_FIELD(ext_zvfbfwma)
  BOOL_FIELD(ext_zvfh)
  BOOL_FIELD(ext_zvfhmin)
+BOOL_FIELD(ext_sdext)
  BOOL_FIELD(ext_sdtrig)
  BOOL_FIELD(ext_smaia)
  BOOL_FIELD(ext_ssaia)
diff --git a/target/riscv/machine.c b/target/riscv/machine.c
index 74edb8c2b5..aba162d0f1 100644
--- a/target/riscv/machine.c
+++ b/target/riscv/machine.c
@@ -302,6 +302,25 @@ static const VMStateDescription vmstate_debug =
{
          VMSTATE_VARRAY_UINT32(env.tdata3, RISCVCPU,
                                env.num_triggers, 0,
                                vmstate_info_uint64, uint64_t),
+        VMSTATE_BOOL_V(env.debug_mode, RISCVCPU, 3),
+        VMSTATE_UINTTL_V(env.dcsr, RISCVCPU, 3),
+        VMSTATE_UINTTL_V(env.dpc, RISCVCPU, 3),
+        VMSTATE_UINTTL_ARRAY_V(env.dscratch, RISCVCPU, 2, 3),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static const VMStateDescription vmstate_sdext = {
+    .name = "cpu/sdext",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = debug_needed,
+    .post_load = debug_post_load,
+    .fields = (const VMStateField[]) {
+        VMSTATE_BOOL_V(env.debug_mode, RISCVCPU, 3),
+        VMSTATE_UINTTL_V(env.dcsr, RISCVCPU, 3),
+        VMSTATE_UINTTL_V(env.dpc, RISCVCPU, 3),
+        VMSTATE_UINTTL_ARRAY_V(env.dscratch, RISCVCPU, 2, 3),
          VMSTATE_END_OF_LIST()
      }
  };
@@ -577,6 +596,7 @@ const VMStateDescription vmstate_riscv_cpu = {
          &vmstate_ctr,
          &vmstate_sstc,
          &vmstate_mseccfg,
+        &vmstate_sdext,
          NULL
      }
  };
diff --git a/target/riscv/tcg/csr.c b/target/riscv/tcg/csr.c
index bd4b6dc114..988261cccf 100644
--- a/target/riscv/tcg/csr.c
+++ b/target/riscv/tcg/csr.c
@@ -3207,6 +3207,126 @@ static RISCVException
write_mtval(CPURISCVState *env, int csrno,
      return RISCV_EXCP_NONE;
  }
+#if !defined(CONFIG_USER_ONLY)
+static RISCVException sdext(CPURISCVState *env, int csrno)
+{
+    if (!riscv_cpu_cfg(env)->ext_sdext) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    if (!env->debug_mode && !env->debugger) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    return RISCV_EXCP_NONE;
+}
+
+static target_ulong dcsr_visible_mask(CPURISCVState *env)
+{
+    target_ulong mask = (target_ulong)-1;

This should be a 32-bit value, as the register is always 32-bit

Alistair

+    RISCVCPU *cpu = env_archcpu(env);
+
+    if (!riscv_has_ext(env, RVH)) {
+        mask &= ~(DCSR_EBREAKVS | DCSR_EBREAKVU | DCSR_V);
+    }
+    if (!riscv_has_ext(env, RVS)) {
+        mask &= ~DCSR_EBREAKS;
+    }
+    if (!riscv_has_ext(env, RVU)) {
+        mask &= ~DCSR_EBREAKU;
+    }
+    if (!cpu->cfg.ext_zicfilp) {
+        mask &= ~DCSR_PELP;
+    }
+    if (!cpu->cfg.ext_smdbltrp) {
+        mask &= ~DCSR_CETRIG;
+    }
+
+    return mask;
+}
+
+static RISCVException read_dcsr(CPURISCVState *env, int csrno,
+                                target_ulong *val)
+{
+    *val = env->dcsr & dcsr_visible_mask(env);
+    return RISCV_EXCP_NONE;
+}
+
+static target_ulong dcsr_writable_mask(CPURISCVState *env)
+{
+    target_ulong mask = DCSR_EBREAKM | DCSR_EBREAKS | DCSR_EBREAKU |
+                        DCSR_STEPIE | DCSR_STOPCOUNT | DCSR_STOPTIME
|
+                        DCSR_STEP | DCSR_PRV_MASK;
+    RISCVCPU *cpu = env_archcpu(env);
+
+    mask |= DCSR_MPRVEN;
+
+    if (riscv_has_ext(env, RVH)) {
+        mask |= DCSR_EBREAKVS | DCSR_EBREAKVU | DCSR_V;
+    }
+    if (riscv_has_ext(env, RVS)) {
+        mask |= DCSR_EBREAKS;
+    }
+    if (riscv_has_ext(env, RVU)) {
+        mask |= DCSR_EBREAKU;
+    }
+    if (cpu->cfg.ext_zicfilp) {
+        mask |= DCSR_PELP;
+    }
+    if (cpu->cfg.ext_smdbltrp) {
+        mask |= DCSR_CETRIG;
+    }
+
+    return mask;
+}
+
+static RISCVException write_dcsr(CPURISCVState *env, int csrno,
+                                 target_ulong val, uintptr_t ra)
+{
+    target_ulong mask = dcsr_writable_mask(env);
+    target_ulong new_val = env->dcsr;
+
+    new_val &= ~mask;
+    new_val |= val & mask;
+    new_val &= ~DCSR_XDEBUGVER_MASK;
+    new_val |= DCSR_DEBUGVER(4);
+    env->dcsr = new_val;
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException read_dpc(CPURISCVState *env, int csrno,
+                               target_ulong *val)
+{
+    *val = env->dpc & get_xepc_mask(env);
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException write_dpc(CPURISCVState *env, int csrno,
+                                target_ulong val, uintptr_t ra)
+{
+    env->dpc = val & get_xepc_mask(env);
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException read_dscratch(CPURISCVState *env, int csrno,
+                                    target_ulong *val)
+{
+    int index = (csrno == CSR_DSCRATCH1) ? 1 : 0;
+
+    *val = env->dscratch[index];
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException write_dscratch(CPURISCVState *env, int csrno,
+                                     target_ulong val, uintptr_t ra)
+{
+    int index = (csrno == CSR_DSCRATCH1) ? 1 : 0;
+
+    env->dscratch[index] = val;
+    return RISCV_EXCP_NONE;
+}
+#endif /* !CONFIG_USER_ONLY */
+
  /* Execution environment configuration setup */
  static RISCVException read_menvcfg(CPURISCVState *env, int csrno,
                                     target_ulong *val)
@@ -6435,6 +6555,12 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] =
{
      [CSR_TDATA3]    =  { "tdata3",   debug, read_tdata,
write_tdata    },
      [CSR_TINFO]     =  { "tinfo",    debug, read_tinfo,
write_ignore   },
      [CSR_MCONTEXT]  =  { "mcontext", debug, read_mcontext,
write_mcontext },
+#if !defined(CONFIG_USER_ONLY)
+    [CSR_DCSR]      =  { "dcsr",      sdext, read_dcsr,
write_dcsr },
+    [CSR_DPC]       =  { "dpc",       sdext, read_dpc,
write_dpc },
+    [CSR_DSCRATCH]  =  { "dscratch0", sdext, read_dscratch,
write_dscratch },
+    [CSR_DSCRATCH1] =  { "dscratch1", sdext, read_dscratch,
write_dscratch },
+#endif
     [CSR_MCTRCTL]    = { "mctrctl",    ctr_mmode,  NULL, NULL,
rmw_xctrctl    },
      [CSR_SCTRCTL]    = { "sctrctl",    ctr_smode,  NULL, NULL,
rmw_xctrctl    },


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