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.

Signed-off-by: Jim Wilson <jimw@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20190212230903.9215-1-jimw@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

2 files changed, 30 insertions, 7 deletions

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 5c2aebf..4c5de30 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -172,6 +172,9 @@ struct CPURISCVState {
 
     /* physical memory protection */
     pmp_table_t pmp_state;
+
+    /* True if in debugger mode.  */
+    bool debugger;
 #endif
 
     float_status fp_status;
@@ -293,6 +296,8 @@ 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)
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 960d2b0..9a40b4c 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -46,7 +46,7 @@ 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
@@ -92,7 +92,7 @@ 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
@@ -103,7 +103,7 @@ 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;
@@ -115,7 +115,7 @@ 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
@@ -126,7 +126,7 @@ 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;
@@ -138,7 +138,7 @@ 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
@@ -150,7 +150,7 @@ 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;
@@ -827,6 +827,24 @@ 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 */