Index: test/SemaObjC/nsobject-attribute.m
===================================================================
--- test/SemaObjC/nsobject-attribute.m	(revision 77004)
+++ test/SemaObjC/nsobject-attribute.m	(working copy)
@@ -26,7 +26,7 @@ id getProperty(id self) {
 @synthesize x=x;
 @end
 
-int main(char *argc, char *argv[]) {
+int main(int argc, char *argv[]) {
     HandTested *to;
     to.x = tmp;  // setter
     if (tmp != to.x)
Index: test/Sema/block-args.c
===================================================================
--- test/Sema/block-args.c	(revision 77004)
+++ test/Sema/block-args.c	(working copy)
@@ -22,7 +22,7 @@ void test() {
   ^(int x, ...){return 5;}(arg, arg);   // Explicit varargs, ok.
 }
 
-int main(int argc) {
+int main(int argc, char** argv) {
   ^(int argCount) {
     argCount = 3;
   }(argc);
Index: test/CXX/basic/basic.start/basic.start.main/p2a.cpp
===================================================================
--- test/CXX/basic/basic.start/basic.start.main/p2a.cpp	(revision 0)
+++ test/CXX/basic/basic.start/basic.start.main/p2a.cpp	(revision 0)
@@ -0,0 +1,8 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+typedef int Int;
+typedef char Char;
+typedef Char* Carp;
+
+Int main(Int argc, Carp argv[]) {
+}
Index: test/CXX/basic/basic.start/basic.start.main/p2b.cpp
===================================================================
--- test/CXX/basic/basic.start/basic.start.main/p2b.cpp	(revision 0)
+++ test/CXX/basic/basic.start/basic.start.main/p2b.cpp	(revision 0)
@@ -0,0 +1,8 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+typedef int Int;
+typedef char Char;
+typedef Char* Carp;
+
+Int main(Int argc, Carp argv[], Char *env[]) {
+}
Index: test/CXX/basic/basic.start/basic.start.main/p2c.cpp
===================================================================
--- test/CXX/basic/basic.start/basic.start.main/p2c.cpp	(revision 0)
+++ test/CXX/basic/basic.start/basic.start.main/p2c.cpp	(revision 0)
@@ -0,0 +1,4 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+int main() {
+}
Index: test/CXX/basic/basic.start/basic.start.main/p2d.cpp
===================================================================
--- test/CXX/basic/basic.start/basic.start.main/p2d.cpp	(revision 0)
+++ test/CXX/basic/basic.start/basic.start.main/p2d.cpp	(revision 0)
@@ -0,0 +1,4 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+static int main() { // expected-error {{'main' is not allowed to be declared static}}
+}
Index: test/CXX/basic/basic.start/basic.start.main/p2e.cpp
===================================================================
--- test/CXX/basic/basic.start/basic.start.main/p2e.cpp	(revision 0)
+++ test/CXX/basic/basic.start/basic.start.main/p2e.cpp	(revision 0)
@@ -0,0 +1,4 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+inline int main() { // expected-error {{'main' is not allowed to be declared inline}}
+}
Index: test/CXX/basic/basic.start/basic.start.main/p2f.cpp
===================================================================
--- test/CXX/basic/basic.start/basic.start.main/p2f.cpp	(revision 0)
+++ test/CXX/basic/basic.start/basic.start.main/p2f.cpp	(revision 0)
@@ -0,0 +1,7 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+void  // expected-error {{error: 'main' must return 'int'}}
+main( // expected-error {{error: first argument of 'main' should be of type 'int'}}
+     float a
+) {
+}
Index: test/CXX/basic/basic.start/basic.start.main/p2g.cpp
===================================================================
--- test/CXX/basic/basic.start/basic.start.main/p2g.cpp	(revision 0)
+++ test/CXX/basic/basic.start/basic.start.main/p2g.cpp	(revision 0)
@@ -0,0 +1,4 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+int main(int argc, const char* const* argv) {
+}
Index: test/CodeGen/volatile.c
===================================================================
--- test/CodeGen/volatile.c	(revision 77004)
+++ test/CodeGen/volatile.c	(working copy)
@@ -38,7 +38,7 @@ volatile extv4 vVE;
 
 volatile struct {int x;} aggFct(void);
 
-void main() {
+int main() {
   int i;
 
   // load
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td	(revision 77004)
+++ include/clang/Basic/DiagnosticSemaKinds.td	(working copy)
@@ -126,6 +126,19 @@ def err_builtin_definition : Error<"defi
 def err_types_compatible_p_in_cplusplus : Error<
   "__builtin_types_compatible_p is not valid in C++">;
 
+/// main()
+// static/inline main() are not errors in C, just in C++.
+def warn_unusual_main_decl : Warning<"'main' should not be declared "
+    "%select{static|inline|static or inline}0">;
+def err_unusual_main_decl : Error<"'main' is not allowed to be declared "
+    "%select{static|inline|static or inline}0">;
+def err_main_returns_nonint : Error<"'main' must return 'int'">;
+def err_main_surplus_args : Error<"%0 is too many arguments for 'main': "
+    "must be 0, 2, or 3">;
+def warn_main_one_arg : Warning<"one-argument 'main' is usually a mistake">;
+def err_main_arg_wrong : Error<"%select{first|second|third}0 argument of "
+    "'main' should be of type %1">;
+
 /// parser diagnostics
 def ext_typedef_without_a_name : ExtWarn<"typedef requires a name">;
 def err_statically_allocated_object : Error<
Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp	(revision 77004)
+++ lib/Sema/SemaDecl.cpp	(working copy)
@@ -2767,7 +2767,80 @@ void Sema::CheckFunctionDeclaration(Func
 }
 
 void Sema::CheckMain(FunctionDecl* FD) {
-  // FIXME: implement.
+  // C++ [basic.start.main]p3:  A program that declares main to be inline
+  //   or static is ill-formed.
+  // This is not an error in C, but we can warn about it.
+  if (FD->isInline() || FD->getStorageClass() == FunctionDecl::Static) {
+    unsigned diagID = getLangOptions().CPlusPlus
+      ? diag::err_unusual_main_decl : diag::warn_unusual_main_decl;
+    int which = (FD->getStorageClass() == FunctionDecl::Static)
+              + (FD->isInline() << 1) - 1;
+    Diag(FD->getLocation(), diagID) << which;
+  }
+
+  QualType T = FD->getType();
+  assert(T->isFunctionType() && "function decl is not of function type");
+  const FunctionType* FT = T->getAsFunctionType();
+  
+  if (!Context.hasSameUnqualifiedType(FT->getResultType(), Context.IntTy)) {
+    // TODO: add a replacement fixit to turn the return type into 'int'.
+    Diag(FD->getTypeSpecStartLoc(), diag::err_main_returns_nonint);
+    FD->setInvalidDecl(true);
+  }
+
+  // Treat protoless main() as nullary.
+  if (isa<FunctionNoProtoType>(FT)) return;
+
+  const FunctionProtoType* FTP = cast<const FunctionProtoType>(FT);
+  unsigned nparams = FTP->getNumArgs();
+  assert(FD->getNumParams() == nparams);
+
+  if (nparams > 3) {
+    Diag(FD->getLocation(), diag::err_main_surplus_args) << nparams;
+    FD->setInvalidDecl(true);
+    nparams = 3;
+  }
+
+  // FIXME: a lot of the following diagnostics would be improved
+  // if we had some location information about types.
+
+  QualType CharPP =
+    Context.getPointerType(Context.getPointerType(Context.CharTy));
+  QualType Expected[] = { Context.IntTy, CharPP, CharPP };
+
+  for (unsigned i = 0; i < nparams; ++i) {
+    QualType AT = FTP->getArgType(i);
+
+    bool mismatch;
+    if (Context.hasSameUnqualifiedType(AT, Expected[i]))
+      mismatch = false;
+    else if (Expected[i] == CharPP) {
+      // As an extension, the following forms are okay:
+      //   char const **
+      //   char const * const *
+      //   char * const *
+      
+      if (const PointerType* PT = AT->getAsPointerType()) {
+        QualType ET = PT->getPointeeType();
+        ET.removeConst();
+        if (!ET.getCVRQualifiers() && (PT = ET->getAsPointerType())) {
+          ET = PT->getPointeeType();
+          ET.removeConst();
+          mismatch = (ET != Context.CharTy);
+        }else mismatch = true;
+      }else mismatch = true;
+    }else mismatch = true;
+
+    if (mismatch) {
+      Diag(FD->getLocation(), diag::err_main_arg_wrong) << i << Expected[i];
+      // TODO: suggest replacing given type with expected type
+      FD->setInvalidDecl(true);
+    }
+  }
+
+  if (nparams == 1 && !FD->isInvalidDecl()) {
+    Diag(FD->getLocation(), diag::warn_main_one_arg);
+  }
 }
 
 bool Sema::CheckForConstantInitializer(Expr *Init, QualType DclT) {