From 00072c08c75050ae2c835b7bb0e505475dbcd7b9 Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Mon, 25 Nov 2019 09:50:58 -0800 Subject: [WebAssembly] Mangle the argc/argv `main` as `__wasm_argc_argv`. WebAssembly enforces a rule that caller and callee signatures must match. This means that the traditional technique of passing `main` `argc` and `argv` even when it doesn't need them doesn't work. Currently the backend renames `main` to `__original_main`, however this doesn't interact well with LTO'ing libc, and the name isn't intuitive. This patch allows us to transition to `__main_argc_argv` instead. This implements the proposal in https://github.com/WebAssembly/tool-conventions/pull/134 with a flag to disable it when targeting Emscripten, though this is expected to be temporary, as discussed in the proposal comments. Differential Revision: https://reviews.llvm.org/D70700 --- clang/lib/CodeGen/CodeGenModule.cpp | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'clang/lib/CodeGen/CodeGenModule.cpp') diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp index 652efd857064..faff623a2973 100644 --- a/clang/lib/CodeGen/CodeGenModule.cpp +++ b/clang/lib/CodeGen/CodeGenModule.cpp @@ -448,6 +448,10 @@ void CodeGenModule::Release() { CodeGenFunction(*this).EmitCfiCheckStub(); } emitAtAvailableLinkGuard(); + if (Context.getTargetInfo().getTriple().isWasm() && + !Context.getTargetInfo().getTriple().isOSEmscripten()) { + EmitMainVoidAlias(); + } emitLLVMUsed(); if (SanStats) SanStats->finish(); @@ -5600,6 +5604,17 @@ void CodeGenModule::EmitDeferredUnusedCoverageMappings() { } } +void CodeGenModule::EmitMainVoidAlias() { + // In order to transition away from "__original_main" gracefully, emit an + // alias for "main" in the no-argument case so that libc can detect when + // new-style no-argument main is in used. + if (llvm::Function *F = getModule().getFunction("main")) { + if (!F->isDeclaration() && F->arg_size() == 0 && !F->isVarArg() && + F->getReturnType()->isIntegerTy(Context.getTargetInfo().getIntWidth())) + addUsedGlobal(llvm::GlobalAlias::create("__main_void", F)); + } +} + /// Turns the given pointer into a constant. static llvm::Constant *GetPointerConstant(llvm::LLVMContext &Context, const void *Ptr) { -- cgit v1.2.3