RISC-V: Add debug support for accessing CSRs.

Add a debugger field to CPURISCVState. Add riscv_csrrw_debug function
to set it. Disable mode checks when debugger field true.

Backports commit 753e3fe207db08ce0ef0405e8452c3397c9b9308 from qemu

qemu/header_gen.py

@@ -5480,6 +5480,7 @@ riscv_symbols = (
     'riscv_cpu_set_mode',
     'riscv_cpu_update_mip',
     'riscv_csrrw',
+    'riscv_csrrw_debug',
     'riscv_excp_names',
     'riscv_fpr_regnames',
     'riscv_get_csr_ops',

qemu/riscv32.h

@@ -3401,6 +3401,7 @@
 #define riscv_cpu_set_mode riscv_cpu_set_mode_riscv32
 #define riscv_cpu_update_mip riscv_cpu_update_mip_riscv32
 #define riscv_csrrw riscv_csrrw_riscv32
+#define riscv_csrrw_debug riscv_csrrw_debug_riscv32
 #define riscv_excp_names riscv_excp_names_riscv32
 #define riscv_fpr_regnames riscv_fpr_regnames_riscv32
 #define riscv_get_csr_ops riscv_get_csr_ops_riscv32

qemu/riscv64.h

@@ -3401,6 +3401,7 @@
 #define riscv_cpu_set_mode riscv_cpu_set_mode_riscv64
 #define riscv_cpu_update_mip riscv_cpu_update_mip_riscv64
 #define riscv_csrrw riscv_csrrw_riscv64
+#define riscv_csrrw_debug riscv_csrrw_debug_riscv64
 #define riscv_excp_names riscv_excp_names_riscv64
 #define riscv_fpr_regnames riscv_fpr_regnames_riscv64
 #define riscv_get_csr_ops riscv_get_csr_ops_riscv64

qemu/target/riscv/cpu.h

@@ -174,6 +174,9 @@ struct CPURISCVState {
 
     /* physical memory protection */
     pmp_table_t pmp_state;
+
+    /* True if in debugger mode.  */
+    bool debugger;
 #endif
 
     float_status fp_status;
@@ -298,6 +301,8 @@ static inline void cpu_get_tb_cpu_state(CPURISCVState *env, target_ulong *pc,
 
 int riscv_csrrw(CPURISCVState *env, int csrno, target_ulong *ret_value,
                 target_ulong new_value, target_ulong write_mask);
+int riscv_csrrw_debug(CPURISCVState *env, int csrno, target_ulong *ret_value,
+                      target_ulong new_value, target_ulong write_mask);
 
 static inline void riscv_csr_write(CPURISCVState *env, int csrno,
                                    target_ulong val)

qemu/target/riscv/csr.c

@@ -45,7 +45,7 @@ void riscv_set_csr_ops(int csrno, riscv_csr_operations *ops)
 static int fs(CPURISCVState *env, int csrno)
 {
 #if !defined(CONFIG_USER_ONLY)
-    if (!(env->mstatus & MSTATUS_FS)) {
+    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
         return -1;
     }
 #endif
@@ -91,7 +91,7 @@ static int pmp(CPURISCVState *env, int csrno)
 static int read_fflags(CPURISCVState *env, int csrno, target_ulong *val)
 {
 #if !defined(CONFIG_USER_ONLY)
-    if (!(env->mstatus & MSTATUS_FS)) {
+    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
         return -1;
     }
 #endif
@@ -102,7 +102,7 @@ static int read_fflags(CPURISCVState *env, int csrno, target_ulong *val)
 static int write_fflags(CPURISCVState *env, int csrno, target_ulong val)
 {
 #if !defined(CONFIG_USER_ONLY)
-    if (!(env->mstatus & MSTATUS_FS)) {
+    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
         return -1;
     }
     env->mstatus |= MSTATUS_FS;
@@ -114,7 +114,7 @@ static int write_fflags(CPURISCVState *env, int csrno, target_ulong val)
 static int read_frm(CPURISCVState *env, int csrno, target_ulong *val)
 {
 #if !defined(CONFIG_USER_ONLY)
-    if (!(env->mstatus & MSTATUS_FS)) {
+    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
         return -1;
     }
 #endif
@@ -125,7 +125,7 @@ static int read_frm(CPURISCVState *env, int csrno, target_ulong *val)
 static int write_frm(CPURISCVState *env, int csrno, target_ulong val)
 {
 #if !defined(CONFIG_USER_ONLY)
-    if (!(env->mstatus & MSTATUS_FS)) {
+    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
         return -1;
     }
     env->mstatus |= MSTATUS_FS;
@@ -137,7 +137,7 @@ static int write_frm(CPURISCVState *env, int csrno, target_ulong val)
 static int read_fcsr(CPURISCVState *env, int csrno, target_ulong *val)
 {
 #if !defined(CONFIG_USER_ONLY)
-    if (!(env->mstatus & MSTATUS_FS)) {
+    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
         return -1;
     }
 #endif
@@ -149,7 +149,7 @@ static int read_fcsr(CPURISCVState *env, int csrno, target_ulong *val)
 static int write_fcsr(CPURISCVState *env, int csrno, target_ulong val)
 {
 #if !defined(CONFIG_USER_ONLY)
-    if (!(env->mstatus & MSTATUS_FS)) {
+    if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
         return -1;
     }
     env->mstatus |= MSTATUS_FS;
@@ -835,6 +835,24 @@ int riscv_csrrw(CPURISCVState *env, int csrno, target_ulong *ret_value,
     return 0;
 }
 
+/*
+ * Debugger support.  If not in user mode, set env->debugger before the
+ * riscv_csrrw call and clear it after the call.
+ */
+int riscv_csrrw_debug(CPURISCVState *env, int csrno, target_ulong *ret_value,
+                target_ulong new_value, target_ulong write_mask)
+{
+    int ret;
+#if !defined(CONFIG_USER_ONLY)
+    env->debugger = true;
+#endif
+    ret = riscv_csrrw(env, csrno, ret_value, new_value, write_mask);
+#if !defined(CONFIG_USER_ONLY)
+    env->debugger = false;
+#endif
+    return ret;
+}
+
 /* Control and Status Register function table */
 static riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
     /* User Floating-Point CSRs */