target/xtensa: handle unknown registers in gdbstub

Xtensa cores may have registers of types/sizes not supported by the
gdbstub accessors. Ignore writes to such registers and return zero on
read, but always return correct register size, so that gdb on the other
side is able to access all registers in the packet holding unsupported
registers in the middle. This fixes gdb interaction with cores that have
vector/custom TIE registers.

Cc: qemu-stable@nongnu.org
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/target/xtensa/gdbstub.c b/target/xtensa/gdbstub.c
index fa5469a..da131ae 100644
--- a/target/xtensa/gdbstub.c
+++ b/target/xtensa/gdbstub.c
@@ -58,7 +58,10 @@ int xtensa_cpu_gdb_read_register(CPUState *cs, uint8_t *mem_buf, int n)
         case 8:
             return gdb_get_reg64(mem_buf, float64_val(env->fregs[i].f64));
         default:
-            return 0;
+            qemu_log_mask(LOG_UNIMP, "%s from reg %d of unsupported size %d\n",
+                          __func__, n, reg->size);
+            memset(mem_buf, 0, reg->size);
+            return reg->size;
         }
 
     case 8: /*a*/
@@ -67,6 +70,8 @@ int xtensa_cpu_gdb_read_register(CPUState *cs, uint8_t *mem_buf, int n)
     default:
         qemu_log_mask(LOG_UNIMP, "%s from reg %d of unsupported type %d\n",
                       __func__, n, reg->type);
+        memset(mem_buf, 0, reg->size);
+        return reg->size;
         return 0;
     }
 }
@@ -111,7 +116,9 @@ int xtensa_cpu_gdb_write_register(CPUState *cs, uint8_t *mem_buf, int n)
             env->fregs[reg->targno & 0x0f].f64 = make_float64(tmp);
             return 8;
         default:
-            return 0;
+            qemu_log_mask(LOG_UNIMP, "%s to reg %d of unsupported size %d\n",
+                          __func__, n, reg->size);
+            return reg->size;
         }
 
     case 8: /*a*/
@@ -121,7 +128,7 @@ int xtensa_cpu_gdb_write_register(CPUState *cs, uint8_t *mem_buf, int n)
     default:
         qemu_log_mask(LOG_UNIMP, "%s to reg %d of unsupported type %d\n",
                       __func__, n, reg->type);
-        return 0;
+        return reg->size;
     }
 
     return 4;