Currently the number of registers exposed to GDB is written as magic
numbers in code. Derive the number of registers GDB actually see from
XML files to replace the magic numbers in code later.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 include/exec/gdbstub.h  |  1 +
 scripts/feature_to_c.py | 46 +++++++++++++++++++++++++++++++++++++++--
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
index 3f08093321..9b484d7eef 100644
--- a/include/exec/gdbstub.h
+++ b/include/exec/gdbstub.h
@@ -13,6 +13,7 @@
 typedef struct GDBFeature {
     const char *xmlname;
     const char *xml;
+    int num_regs;
 } GDBFeature;
 
 
diff --git a/scripts/feature_to_c.py b/scripts/feature_to_c.py
index bcbcb83beb..e04d6b2df7 100755
--- a/scripts/feature_to_c.py
+++ b/scripts/feature_to_c.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 # SPDX-License-Identifier: GPL-2.0-or-later
 
-import os, sys
+import os, sys, xml.etree.ElementTree
 
 def writeliteral(indent, bytes):
     sys.stdout.write(' ' * indent)
@@ -39,10 +39,52 @@ def writeliteral(indent, bytes):
     with open(input, 'rb') as file:
         read = file.read()
 
+    parser = xml.etree.ElementTree.XMLPullParser(['start', 'end'])
+    parser.feed(read)
+    events = parser.read_events()
+    event, element = next(events)
+    if event != 'start':
+        sys.stderr.write(f'unexpected event: {event}\n')
+        exit(1)
+    if element.tag != 'feature':
+        sys.stderr.write(f'unexpected start tag: {element.tag}\n')
+        exit(1)
+
+    regnum = 0
+    regnums = []
+    tags = ['feature']
+    for event, element in events:
+        if event == 'end':
+            if element.tag != tags[len(tags) - 1]:
+                sys.stderr.write(f'unexpected end tag: {element.tag}\n')
+                exit(1)
+
+            tags.pop()
+            if element.tag == 'feature':
+                break
+        elif event == 'start':
+            if len(tags) < 2 and element.tag == 'reg':
+                if 'regnum' in element.attrib:
+                    regnum = int(element.attrib['regnum'])
+
+                regnums.append(regnum)
+                regnum += 1
+
+            tags.append(element.tag)
+        else:
+            raise Exception(f'unexpected event: {event}\n')
+
+    if len(tags):
+        sys.stderr.write('unterminated feature tag\n')
+        exit(1)
+
+    base_reg = min(regnums)
+    num_regs = max(regnums) - base_reg + 1 if len(regnums) else 0
+
     sys.stdout.write('    {\n')
     writeliteral(8, bytes(os.path.basename(input), 'utf-8'))
     sys.stdout.write(',\n')
     writeliteral(8, read)
-    sys.stdout.write('\n    },\n')
+    sys.stdout.write(f',\n        {num_regs},\n    }},\n')
 
 sys.stdout.write('    { NULL }\n};\n')
-- 
2.41.0