diff --git a/target-xtensa/core-dc232b.c b/target-xtensa/core-dc232b.c
index a3b914b..06826c0 100644
--- a/target-xtensa/core-dc232b.c
+++ b/target-xtensa/core-dc232b.c
@@ -33,7 +33,7 @@
 #include "core-dc232b/core-isa.h"
 #include "overlay_tool.h"
 
-static const XtensaConfig dc232b __attribute__((unused)) = {
+static XtensaConfig dc232b __attribute__((unused)) = {
     .name = "dc232b",
     .gdb_regmap = {
         .num_regs = 120,
diff --git a/target-xtensa/core-dc233c.c b/target-xtensa/core-dc233c.c
index ac745d1..8daf7d9 100644
--- a/target-xtensa/core-dc233c.c
+++ b/target-xtensa/core-dc233c.c
@@ -34,7 +34,7 @@
 #include "core-dc233c/core-isa.h"
 #include "overlay_tool.h"
 
-static const XtensaConfig dc233c __attribute__((unused)) = {
+static XtensaConfig dc233c __attribute__((unused)) = {
     .name = "dc233c",
     .gdb_regmap = {
         .num_regs = 121,
diff --git a/target-xtensa/core-fsf.c b/target-xtensa/core-fsf.c
index cfcc840..f6ea6b9 100644
--- a/target-xtensa/core-fsf.c
+++ b/target-xtensa/core-fsf.c
@@ -33,9 +33,14 @@
 #include "core-fsf/core-isa.h"
 #include "overlay_tool.h"
 
-static const XtensaConfig fsf __attribute__((unused)) = {
+static XtensaConfig fsf __attribute__((unused)) = {
     .name = "fsf",
+    .gdb_regmap = {
     /* GDB for this core is not supported currently */
+        .reg = {
+            XTREG_END
+        },
+    },
     .clock_freq_khz = 10000,
     DEFAULT_SECTIONS
 };
diff --git a/target-xtensa/cpu.h b/target-xtensa/cpu.h
index b592efb..b89c602 100644
--- a/target-xtensa/cpu.h
+++ b/target-xtensa/cpu.h
@@ -400,6 +400,7 @@ XtensaCPU *cpu_xtensa_init(const char *cpu_model);
 void xtensa_translate_init(void);
 void xtensa_breakpoint_handler(CPUState *cs);
 int cpu_xtensa_exec(CPUXtensaState *s);
+void xtensa_finalize_config(XtensaConfig *config);
 void xtensa_register_core(XtensaConfigList *node);
 void check_interrupts(CPUXtensaState *s);
 void xtensa_irq_init(CPUXtensaState *env);
diff --git a/target-xtensa/helper.c b/target-xtensa/helper.c
index d84d259..76be50d 100644
--- a/target-xtensa/helper.c
+++ b/target-xtensa/helper.c
@@ -51,6 +51,20 @@ static void xtensa_core_class_init(ObjectClass *oc, void *data)
     cc->gdb_num_core_regs = config->gdb_regmap.num_regs;
 }
 
+void xtensa_finalize_config(XtensaConfig *config)
+{
+    unsigned i, n = 0;
+
+    if (config->gdb_regmap.num_regs) {
+        return;
+    }
+
+    for (i = 0; config->gdb_regmap.reg[i].targno >= 0; ++i) {
+        n += (config->gdb_regmap.reg[i].type != 6);
+    }
+    config->gdb_regmap.num_regs = n;
+}
+
 void xtensa_register_core(XtensaConfigList *node)
 {
     TypeInfo type = {
diff --git a/target-xtensa/import_core.sh b/target-xtensa/import_core.sh
index 73791ec..351bee4 100755
--- a/target-xtensa/import_core.sh
+++ b/target-xtensa/import_core.sh
@@ -22,8 +22,7 @@ mkdir -p "$TARGET"
 tar -xf "$OVERLAY" -C "$TARGET" --strip-components=1 \
     --xform='s/core/core-isa/' config/core.h
 tar -xf "$OVERLAY" -O gdb/xtensa-config.c | \
-    sed -n '1,/*\//p;/pc/,/a15/p' > "$TARGET"/gdb-config.c
-NUM_REGS=$(grep XTREG "$TARGET"/gdb-config.c | wc -l)
+    sed -n '1,/*\//p;/XTREG/,/XTREG_END/p' > "$TARGET"/gdb-config.c
 
 cat <<EOF > "${TARGET}.c"
 #include "cpu.h"
@@ -34,10 +33,9 @@ cat <<EOF > "${TARGET}.c"
 #include "core-$NAME/core-isa.h"
 #include "overlay_tool.h"
 
-static const XtensaConfig $NAME __attribute__((unused)) = {
+static XtensaConfig $NAME __attribute__((unused)) = {
     .name = "$NAME",
     .gdb_regmap = {
-        .num_regs = $NUM_REGS,
         .reg = {
 #include "core-$NAME/gdb-config.c"
         }
diff --git a/target-xtensa/overlay_tool.h b/target-xtensa/overlay_tool.h
index f7b1510..eda03aa 100644
--- a/target-xtensa/overlay_tool.h
+++ b/target-xtensa/overlay_tool.h
@@ -28,6 +28,7 @@
 #define XTREG(idx, ofs, bi, sz, al, no, flags, cp, typ, grp, name, \
         a1, a2, a3, a4, a5, a6) \
     { .targno = (no), .type = (typ), .group = (grp), .size = (sz) },
+#define XTREG_END { .targno = -1 },
 
 #ifndef XCHAL_HAVE_DIV32
 #define XCHAL_HAVE_DIV32 0
@@ -316,6 +317,7 @@
         static XtensaConfigList node = { \
             .config = &core, \
         }; \
+        xtensa_finalize_config(&core); \
         xtensa_register_core(&node); \
     }
 #else
