[PATCH v6 6/9] docs: add doxygen preprocessor and related files

[Luca Fancellu <luca.fancellu@arm.com>]

Add preprocessor called by doxygen before parsing headers,
it will include in every header a doxygen_include.h file
that provides missing defines and includes that are
usually passed by the compiler.

Add doxy_input.list that is a text file containing the
relative path to the source code file to be parsed by
doxygen. The path sould be relative to the xen folder:
E.g. xen/include/public/grant_table.h

Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
---
 docs/xen-doxygen/doxy-preprocessor.py | 110 ++++++++++++++++++++++++++
 docs/xen-doxygen/doxy_input.list      |   0
 docs/xen-doxygen/doxygen_include.h.in |  32 ++++++++
 3 files changed, 142 insertions(+)
 create mode 100755 docs/xen-doxygen/doxy-preprocessor.py
 create mode 100644 docs/xen-doxygen/doxy_input.list
 create mode 100644 docs/xen-doxygen/doxygen_include.h.in

diff --git a/docs/xen-doxygen/doxy-preprocessor.py b/docs/xen-doxygen/doxy-preprocessor.py
new file mode 100755
index 0000000000..496899d8e6
--- /dev/null
+++ b/docs/xen-doxygen/doxy-preprocessor.py
@@ -0,0 +1,110 @@
+#!/usr/bin/python3
+#
+# Copyright (c) 2021, Arm Limited.
+#
+# SPDX-License-Identifier: GPL-2.0
+#
+
+import os, sys, re
+
+
+# Variables that holds the preprocessed header text
+output_text = ""
+header_file_name = ""
+
+# Variables to enumerate the anonymous structs/unions
+anonymous_struct_count = 0
+anonymous_union_count = 0
+
+
+def error(text):
+    sys.stderr.write("{}\n".format(text))
+    sys.exit(1)
+
+
+def write_to_output(text):
+    sys.stdout.write(text)
+
+
+def insert_doxygen_header(text):
+    # Here the strategy is to insert the #include <doxygen_include.h> in the
+    # first line of the header
+    abspath = os.path.dirname(os.path.abspath(__file__))
+    text += "#include \"{}/doxygen_include.h\"\n".format(abspath)
+
+    return text
+
+
+def enumerate_anonymous(match):
+    global anonymous_struct_count
+    global anonymous_union_count
+
+    if "struct" in match.group(1):
+        label = "anonymous_struct_%d" % anonymous_struct_count
+        anonymous_struct_count += 1
+    else:
+        label = "anonymous_union_%d" % anonymous_union_count
+        anonymous_union_count += 1
+
+    return match.group(1) + " " + label + " {"
+
+
+def manage_anonymous_structs_unions(text):
+    # Match anonymous unions/structs with this pattern:
+    # struct/union {
+    #     [...]
+    #
+    # and substitute it in this way:
+    #
+    # struct anonymous_struct_# {
+    #     [...]
+    # or
+    # union anonymous_union_# {
+    #     [...]
+    # where # is a counter starting from zero, different between structs and
+    # unions
+    #
+    # We don't count anonymous union/struct that are part of a typedef because
+    # they don't create any issue for doxygen
+    text = re.sub(
+        "(?<!typedef\s)(struct|union)\s+?\{",
+        enumerate_anonymous,
+        text,
+        flags=re.S
+    )
+
+    return text
+
+
+def main(argv):
+    global output_text
+    global header_file_name
+
+    if len(argv) != 1:
+        error("Script called without arguments!")
+
+    header_file_name = argv[0]
+
+    # Open header file
+    input_header_file = open(header_file_name, 'r')
+    # Read all lines
+    lines = input_header_file.readlines()
+
+    # Inject config.h and some defines in the current header, during compilation
+    # this job is done by the -include argument passed to the compiler.
+    output_text = insert_doxygen_header(output_text)
+
+    # Load file content in a variable
+    for line in lines:
+        output_text += "{}".format(line)
+
+    # Try to get rid of any anonymous union/struct
+    output_text = manage_anonymous_structs_unions(output_text)
+
+    # Final stage of the preprocessor, print the output to stdout
+    write_to_output(output_text)
+
+
+if __name__ == "__main__":
+    main(sys.argv[1:])
+    sys.exit(0)
diff --git a/docs/xen-doxygen/doxy_input.list b/docs/xen-doxygen/doxy_input.list
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/docs/xen-doxygen/doxygen_include.h.in b/docs/xen-doxygen/doxygen_include.h.in
new file mode 100644
index 0000000000..df284f3931
--- /dev/null
+++ b/docs/xen-doxygen/doxygen_include.h.in
@@ -0,0 +1,32 @@
+/*
+ * Doxygen include header
+ * It supplies the xen/include/xen/config.h that is included using the -include
+ * argument of the compiler in Xen Makefile.
+ * Other macros are defined because they are usually provided by the compiler.
+ *
+ * Copyright (C) 2021 ARM Limited
+ *
+ * Author: Luca Fancellu <luca.fancellu@arm.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0
+ */
+
+#include "@XEN_BASE@/xen/include/xen/config.h"
+
+#if defined(CONFIG_X86_64)
+
+#define __x86_64__ 1
+
+#elif defined(CONFIG_ARM_64)
+
+#define __aarch64__ 1
+
+#elif defined(CONFIG_ARM_32)
+
+#define __arm__ 1
+
+#else
+
+#error Architecture not supported/recognized.
+
+#endif
-- 
2.17.1