Add support for variadic arguments in generated stubs

Previously we were using va_list for variadic arguments. The downside
for this was that only the first value from the variadic argument was
passed to the original function.

To make it work properly we have to use the __VA_ARGS__ variadic macro
that was introduces in C99 and is available in all major C/C++
compilers.

Change-Id: I50652f7348a16214811aaab8af116d78cdb70444
Reviewed-on: https://chromium-review.googlesource.com/c/1323089Reviewed-by: Patrik Höglund <phoglund@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Tomáš Popela <tomas.popela@gmail.com>
Cr-Commit-Position: refs/heads/master@{#606588}

tools/generate_stubs/generate_stubs.py

@@ -17,16 +17,6 @@ or a header + implementation file of stubs suitable for use in a POSIX system.
 
 This script also handles variadic functions, e.g.
 void printf(const char* s, ...);
-
-TODO(hclam): Fix the situation for variadic functions.
-Stub for the above function will be generated and inside the stub function it
-is translated to:
-void printf(const char* s, ...) {
-  printf_ptr(s, (void*)arg1);
-}
-
-Only one argument from the variadic arguments is used and it will be used as
-type void*.
 """
 
 __author__ = 'ajwong@chromium.org (Albert J. Wong)'
@@ -111,11 +101,9 @@ STUB_FUNCTION_DEFINITION = (
 VARIADIC_STUB_FUNCTION_DEFINITION = (
     """extern %(return_type)s %(name)s(%(params)s) __attribute__((weak));
 %(return_type)s %(export)s %(name)s(%(params)s) {
-  va_list args___;
-  va_start(args___, %(last_named_arg)s);
-  %(return_type)s ret___ = %(name)s_ptr(%(arg_list)s, va_arg(args___, void*));
-  va_end(args___);
-  return ret___;
+#define %(name)s_ptr_variadic(%(arg_list)s, ...) \
+%(name)s_ptr(%(arg_list)s, ##__VA_ARGS__)
+  return %(name)s_ptr_variadic(%(arg_list)s);
 }""")
 
 # Template for generating a variadic stub function definition without
@@ -132,10 +120,9 @@ VARIADIC_STUB_FUNCTION_DEFINITION = (
 VOID_VARIADIC_STUB_FUNCTION_DEFINITION = (
     """extern void %(name)s(%(params)s) __attribute__((weak));
 void %(export)s %(name)s(%(params)s) {
-  va_list args___;
-  va_start(args___, %(last_named_arg)s);
-  %(name)s_ptr(%(arg_list)s, va_arg(args___, void*));
-  va_end(args___);
+#define %(name)s_ptr_variadic(%(arg_list)s, ...) \
+%(name)s_ptr(%(arg_list)s, ##__VA_ARGS__)
+  %(name)s_ptr_variadic(%(arg_list)s);
 }""")
 
 # Template for the preamble for the stub header file with the header guards,

tools/generate_stubs/generate_stubs_unittest.py

@@ -42,6 +42,8 @@ SIMPLE_SIGNATURES = [
     ('int corge(void);', _MakeSignature('int', 'corge', ['void'])),
     ('int ferda(char **argv[]);',
      _MakeSignature('int', 'ferda', ['char **argv[]'])),
+    ('void brouk(char *pytlik, ...);',
+     _MakeSignature('void', 'brouk', ['char *pytlik', '...'])),
     ]
 
 TRICKY_SIGNATURES = [
@@ -221,6 +223,14 @@ int  ferda(char **argv[]) {
   return ferda_ptr(argv);
 }""", gs.PosixStubWriter.StubFunction(SIMPLE_SIGNATURES[6][1]))
 
+    # Test variadic argument
+    self.assertEqual("""extern void brouk(char *pytlik, ...) \
+__attribute__((weak));
+void  brouk(char *pytlik, ...) {
+#define brouk_ptr_variadic(pytlik, ...) brouk_ptr(pytlik, ##__VA_ARGS__)
+  brouk_ptr_variadic(pytlik);
+}""", gs.PosixStubWriter.StubFunction(SIMPLE_SIGNATURES[7][1]))
+
   def testWriteImplemenationContents(self):
     outfile = StringIO.StringIO()
     self.writer.WriteImplementationContents('my_namespace', outfile)