diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 9540091a82cd..9d2b2a9adf5f 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -126,6 +126,19 @@ def err_builtin_definition : Error<"definition of builtin function %0">;
 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<
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 454896584f29..91de9989360c 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2767,7 +2767,85 @@ void Sema::CheckFunctionDeclaration(FunctionDecl *NewFD, NamedDecl *&PrevDecl,
 }
 
 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.
+  // C99 6.7.4p4:  In a hosted environment, the inline function specifier
+  //   shall not appear in a declaration of main.
+  // static main is not an error under C99, but we should warn about it.
+  bool isInline = FD->isInline();
+  bool isStatic = FD->getStorageClass() == FunctionDecl::Static;
+  if (isInline || isStatic) {
+    unsigned diagID = diag::warn_unusual_main_decl;
+    if (isInline || getLangOptions().CPlusPlus)
+      diagID = diag::err_unusual_main_decl;
+
+    int which = isStatic + (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 = true;
+
+    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 *
+
+      QualifierSet qs;
+      const PointerType* PT;
+      if ((PT = qs.strip(AT)->getAsPointerType()) &&
+          (PT = qs.strip(PT->getPointeeType())->getAsPointerType()) &&
+          (QualType(qs.strip(PT->getPointeeType()), 0) == Context.CharTy)) {
+        qs.removeConst();
+        mismatch = !qs.empty();
+      }
+    }
+
+    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) {
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p2a.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p2a.cpp
new file mode 100644
index 000000000000..a6a758798949
--- /dev/null
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p2a.cpp
@@ -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[]) {
+}
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p2b.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p2b.cpp
new file mode 100644
index 000000000000..caecf6060881
--- /dev/null
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p2b.cpp
@@ -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[]) {
+}
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p2c.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p2c.cpp
new file mode 100644
index 000000000000..8587d8cec791
--- /dev/null
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p2c.cpp
@@ -0,0 +1,4 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+int main() {
+}
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p2d.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p2d.cpp
new file mode 100644
index 000000000000..777b5ceb743a
--- /dev/null
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p2d.cpp
@@ -0,0 +1,4 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+static int main() { // expected-error {{'main' is not allowed to be declared static}}
+}
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p2e.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p2e.cpp
new file mode 100644
index 000000000000..087cf77476ad
--- /dev/null
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p2e.cpp
@@ -0,0 +1,4 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+inline int main() { // expected-error {{'main' is not allowed to be declared inline}}
+}
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p2f.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p2f.cpp
new file mode 100644
index 000000000000..b7845b13e9a4
--- /dev/null
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p2f.cpp
@@ -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
+) {
+}
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p2g.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p2g.cpp
new file mode 100644
index 000000000000..4cedcdb91657
--- /dev/null
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p2g.cpp
@@ -0,0 +1,4 @@
+// RUN: clang-cc -fsyntax-only -verify %s 
+
+int main(int argc, const char* const* argv) {
+}
diff --git a/clang/test/CodeGen/volatile.c b/clang/test/CodeGen/volatile.c
index 212a0aeb1e35..87cb5ff4eb4f 100644
--- a/clang/test/CodeGen/volatile.c
+++ b/clang/test/CodeGen/volatile.c
@@ -38,7 +38,7 @@ volatile extv4 vVE;
 
 volatile struct {int x;} aggFct(void);
 
-void main() {
+int main() {
   int i;
 
   // load
diff --git a/clang/test/Sema/block-args.c b/clang/test/Sema/block-args.c
index 27bee77da6c6..3a58735f23a3 100644
--- a/clang/test/Sema/block-args.c
+++ b/clang/test/Sema/block-args.c
@@ -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);
diff --git a/clang/test/SemaObjC/nsobject-attribute.m b/clang/test/SemaObjC/nsobject-attribute.m
index 3544cb139aab..c47b909846c1 100644
--- a/clang/test/SemaObjC/nsobject-attribute.m
+++ b/clang/test/SemaObjC/nsobject-attribute.m
@@ -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)