compat: Consolidate mingw-w64 ASLR workaround for upstream libsecp changes

Achieve this by adding a MAIN_FUNCTION macro, consolidating the docs, and
introducing the macro across our distributed binaries.

Also update the docs to explain that anyone using binutils < 2.36 is
effected by this issue. Release builds are not, because they use binutils
2.37. Currently LTS Linux distros, like Ubuntu Focal, ship with 2.34.

https://packages.ubuntu.com/focal/binutils

src/bitcoin-cli.cpp

@@ -9,6 +9,7 @@
 
 #include <chainparamsbase.h>
 #include <clientversion.h>
+#include <compat.h>
 #include <compat/stdin.h>
 #include <policy/feerate.h>
 #include <rpc/client.h>
@@ -1212,19 +1213,11 @@ static int CommandLineRPC(int argc, char *argv[])
     return nRet;
 }
 
-#ifdef WIN32
-// Export main() and ensure working ASLR on Windows.
-// Exporting a symbol will prevent the linker from stripping
-// the .reloc section from the binary, which is a requirement
-// for ASLR. This is a temporary workaround until a fixed
-// version of binutils is used for releases.
-__declspec(dllexport) int main(int argc, char* argv[])
+MAIN_FUNCTION
 {
+#ifdef WIN32
     util::WinCmdLineArgs winArgs;
     std::tie(argc, argv) = winArgs.get();
-#else
-int main(int argc, char* argv[])
-{
 #endif
     SetupEnvironment();
     if (!SetupNetworking()) {

src/bitcoin-tx.cpp

@@ -8,6 +8,7 @@
 
 #include <clientversion.h>
 #include <coins.h>
+#include <compat.h>
 #include <consensus/amount.h>
 #include <consensus/consensus.h>
 #include <core_io.h>
@@ -854,7 +855,7 @@ static int CommandLineRawTx(int argc, char* argv[])
     return nRet;
 }
 
-int main(int argc, char* argv[])
+MAIN_FUNCTION
 {
     SetupEnvironment();
 

src/bitcoin-util.cpp

@@ -11,6 +11,7 @@
 #include <chainparams.h>
 #include <chainparamsbase.h>
 #include <clientversion.h>
+#include <compat.h>
 #include <core_io.h>
 #include <streams.h>
 #include <util/system.h>
@@ -142,16 +143,7 @@ static int Grind(const std::vector<std::string>& args, std::string& strPrint)
     return EXIT_SUCCESS;
 }
 
-#ifdef WIN32
-// Export main() and ensure working ASLR on Windows.
-// Exporting a symbol will prevent the linker from stripping
-// the .reloc section from the binary, which is a requirement
-// for ASLR. This is a temporary workaround until a fixed
-// version of binutils is used for releases.
-__declspec(dllexport) int main(int argc, char* argv[])
-#else
-int main(int argc, char* argv[])
-#endif
+MAIN_FUNCTION
 {
     ArgsManager& args = gArgs;
     SetupEnvironment();

src/bitcoin-wallet.cpp

@@ -9,6 +9,7 @@
 #include <chainparams.h>
 #include <chainparamsbase.h>
 #include <clientversion.h>
+#include <compat.h>
 #include <interfaces/init.h>
 #include <key.h>
 #include <logging.h>
@@ -88,7 +89,7 @@ static bool WalletAppInit(ArgsManager& args, int argc, char* argv[])
     return true;
 }
 
-int main(int argc, char* argv[])
+MAIN_FUNCTION
 {
     ArgsManager& args = gArgs;
 #ifdef WIN32

src/bitcoind.cpp

@@ -256,7 +256,7 @@ static bool AppInit(NodeContext& node, int argc, char* argv[])
     return fRet;
 }
 
-int main(int argc, char* argv[])
+MAIN_FUNCTION
 {
 #ifdef WIN32
     util::WinCmdLineArgs winArgs;

src/compat.h

@@ -86,6 +86,17 @@ typedef void* sockopt_arg_type;
 typedef char* sockopt_arg_type;
 #endif
 
+#ifdef WIN32
+// Export main() and ensure working ASLR when using mingw-w64.
+// Exporting a symbol will prevent the linker from stripping
+// the .reloc section from the binary, which is a requirement
+// for ASLR. While release builds are not affected, anyone
+// building with a binutils < 2.36 is subject to this ld bug.
+#define MAIN_FUNCTION __declspec(dllexport) int main(int argc, char* argv[])
+#else
+#define MAIN_FUNCTION int main(int argc, char* argv[])
+#endif
+
 // Note these both should work with the current usage of poll, but best to be safe
 // WIN32 poll is broken https://daniel.haxx.se/blog/2012/10/10/wsapoll-is-broken/
 // __APPLE__ poll is broke https://github.com/bitcoin/bitcoin/pull/14336#issuecomment-437384408

src/qt/main.cpp

@@ -4,6 +4,7 @@
 
 #include <qt/bitcoin.h>
 
+#include <compat.h>
 #include <util/translation.h>
 #include <util/url.h>
 
@@ -18,4 +19,7 @@ extern const std::function<std::string(const char*)> G_TRANSLATION_FUN = [](cons
 };
 UrlDecodeFn* const URL_DECODE = urlDecode;
 
-int main(int argc, char* argv[]) { return GuiMain(argc, argv); }
+MAIN_FUNCTION
+{
+    return GuiMain(argc, argv);
+}