driver: Support code for shared library collision detection.

driver/main.cpp

@@ -847,6 +847,27 @@ void genCmain(Scope *sc)
     rootHasMain = sc->module;
 }
 
+/// Emits a declaration for the given symbol, which is assumed to be of type
+/// i8*, and defines a second globally visible i8* that contains the address
+/// of the first symbol.
+static void emitSymbolAddrGlobal(llvm::Module& lm, const char* symbolName,
+    const char* addrName)
+{
+    llvm::Type* voidPtr = llvm::PointerType::get(
+        llvm::Type::getInt8Ty(lm.getContext()), 0);
+    llvm::GlobalVariable* targetSymbol = new llvm::GlobalVariable(
+        lm, voidPtr, false, llvm::GlobalValue::ExternalLinkage,
+        NULL, symbolName
+    );
+    new llvm::GlobalVariable(lm, voidPtr, false,
+        llvm::GlobalValue::ExternalLinkage,
+        llvm::ConstantExpr::getBitCast(targetSymbol, voidPtr),
+        addrName
+    );
+}
+
+/// Adds the __entrypoint module and related support code into the given LLVM
+/// module. This assumes that genCmain() has already been called.
 static void emitEntryPointInto(llvm::Module* lm)
 {
     assert(entrypoint && "Entry point Dmodule has not been generated.");
@@ -856,7 +877,16 @@ static void emitEntryPointInto(llvm::Module* lm)
     llvm::Linker linker("ldc", lm);
 #endif
 
-    llvm::Module* entryModule = entrypoint->genLLVMModule(lm->getContext());
+    llvm::LLVMContext& context = lm->getContext();
+    llvm::Module* entryModule = entrypoint->genLLVMModule(context);
+
+    // On Linux, strongly define the excecutabe BSS bracketing symbols in the
+    // main module for druntime use (see rt.sections_linux).
+    if (global.params.isLinux)
+    {
+        emitSymbolAddrGlobal(*entryModule, "__bss_start", "_d_execBssBegAddr");
+        emitSymbolAddrGlobal(*entryModule, "_end", "_d_execBssEndAddr");
+    }
 
     std::string linkError;
 #if LDC_LLVM_VER >= 303