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>
(cherry picked from commit dd7b952b793e341c905355581a21cdbaa8b13c31)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/target/xtensa/gdbstub.c b/target/xtensa/gdbstub.c
index fa5469a4ef5f5b6053ea377b379f48ac0770d02d..da131ae8ccd11c4ec4727d0138ec01600934864b 100644 (file)
--- 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;