generator: fix align-pads for switches which start at unaligned pos

Fix the alignment computation inside switches which start at
an unaligned pos.
This affects both explicit and implicit align pads.

The alignment offset is derived from the lowest 3 bits of
the pointer to the protocol-data at the start of the switch.
This is sufficient for correcting all alignments up to 8-byte alignment.
As far as I know there is no bigger alignment than 8-byte for the
X-protocol.

Example:
struct InputState, where the switch starts after two 1-byte fields,
which is a 2 byte offset for 4-byte and 8-byte alignment.

The previous problem can be demonstrated when adding a
<pad align="4"/> at the end of case "key".

(Or when finding a testcase which reports the case "valuator" not
at the last position of the QueryDeviceState-reply.
I didn't find such a testcase, so I have used the pad align
as described above.)

V2: patch modified in order to fix bugs which I found when working on the
next issue:
* xcb_padding_offset has to be set 0 when xcb_block_len is set 0
* xcb_padding_offset cannot be "const" therefore
* for unpack and unserialize, the padding_offset must computed
  from _buffer instead of from the aux_var.

V3: patch revised according to suggestion by Ran Benita:
* only create and use xcb_padding_offset for switch

Message-ID: <1410298000-24734-1-git-send-email-chris@demorecorder.com>
Patch-Thread-Subject: [Xcb] xinput:QueryDeviceState: full-support: generator and xml-changes
Patch-Set: QueryDeviceState
Patch-Number: libxcb 4/4
Patch-Version: V3
Signed-off-by: Christian Linhart <chris@DemoRecorder.com>
Reviewed-By: Ran Benita <ran234@gmail.com>

1 files changed, 21 insertions, 5 deletions

diff --git a/src/c_client.py b/src/c_client.py
index 1d1bbf6..0a1f877 100644
--- a/src/c_client.py
+++ b/src/c_client.py
@@ -657,9 +657,15 @@ def get_serialize_params(context, self, buffer_var='_buffer', aux_var='_aux'):
     return (param_fields, wire_fields, params)
 # get_serialize_params()
 
-def _c_serialize_helper_insert_padding(context, code_lines, space, postpone):
+def _c_serialize_helper_insert_padding(context, code_lines, space, postpone, is_case_or_bitcase):
     code_lines.append('%s    /* insert padding */' % space)
-    code_lines.append('%s    xcb_pad = -xcb_block_len & (xcb_align_to - 1);' % space)
+    if is_case_or_bitcase:
+        code_lines.append(
+            '%s    xcb_pad = -(xcb_block_len + xcb_padding_offset) & (xcb_align_to - 1);'
+            % space)
+    else:
+        code_lines.append(
+            '%s    xcb_pad = -xcb_block_len & (xcb_align_to - 1);' % space)
 #    code_lines.append('%s    printf("automatically inserting padding: %%%%d\\n", xcb_pad);' % space)
     code_lines.append('%s    xcb_buffer_len += xcb_block_len + xcb_pad;' % space)
 
@@ -677,6 +683,8 @@ def _c_serialize_helper_insert_padding(context, code_lines, space, postpone):
         code_lines.append('%s    }' % space)
 
     code_lines.append('%s    xcb_block_len = 0;' % space)
+    if is_case_or_bitcase:
+        code_lines.append('%s    xcb_padding_offset = 0;' % space)
 
     # keep tracking of xcb_parts entries for serialize
     return 1
@@ -1005,13 +1013,15 @@ def _c_serialize_helper_fields(context, self,
                 # Variable length pad is <pad align= />
                 code_lines.append('%s    xcb_align_to = %d;' % (space, field.type.align))
                 count += _c_serialize_helper_insert_padding(context, code_lines, space,
-                                                        self.c_var_followed_by_fixed_fields)
+                                                            self.c_var_followed_by_fixed_fields,
+                                                            is_case_or_bitcase)
                 continue
             else:
                 # switch/bitcase: always calculate padding before and after variable sized fields
                 if need_padding or is_case_or_bitcase:
                     count += _c_serialize_helper_insert_padding(context, code_lines, space,
-                                                            self.c_var_followed_by_fixed_fields)
+                                                                self.c_var_followed_by_fixed_fields,
+                                                                is_case_or_bitcase)
 
                 value, length = _c_serialize_helper_fields_variable_size(context, self, field,
                                                                          code_lines, temp_vars,
@@ -1100,7 +1110,7 @@ def _c_serialize_helper(context, complex_type,
                                             code_lines, temp_vars,
                                             space, prefix, False)
     # "final padding"
-    count += _c_serialize_helper_insert_padding(context, code_lines, space, False)
+    count += _c_serialize_helper_insert_padding(context, code_lines, space, False, self.is_switch)
 
     return count
 # _c_serialize_helper()
@@ -1170,6 +1180,8 @@ def _c_serialize(context, self):
             _c('    char *xcb_out = *_buffer;')
             _c('    unsigned int xcb_buffer_len = 0;')
             _c('    unsigned int xcb_align_to = 0;')
+        if self.is_switch:
+            _c('    unsigned int xcb_padding_offset = ((size_t)xcb_out) & 7;')
         prefix = [('_aux', '->', self)]
         aux_ptr = 'xcb_out'
 
@@ -1193,6 +1205,8 @@ def _c_serialize(context, self):
         _c('    unsigned int xcb_block_len = 0;')
         _c('    unsigned int xcb_pad = 0;')
         _c('    unsigned int xcb_align_to = 0;')
+        if self.is_switch:
+            _c('    unsigned int xcb_padding_offset = ((size_t)_buffer) & 7;')
 
     elif 'sizeof' == context:
         param_names = [p[2] for p in params]
@@ -1210,6 +1224,8 @@ def _c_serialize(context, self):
         else:
             _c('    char *xcb_tmp = (char *)_buffer;')
             prefix = [('_aux', '->', self)]
+            if self.is_switch:
+                _c('    unsigned int xcb_padding_offset = 0;')
 
     count = _c_serialize_helper(context, self, code_lines, temp_vars, prefix=prefix)
     # update variable size fields (only important for context=='serialize'