[clang][clangd] Ensure the stack bottom before building AST

`clang::runWithSufficientStackSpace` requires the address of the
initial stack bottom to prevent potential stack overflows.

In addition, add a fallback to ASTFrontendAction in case any client
forgets to call it when not through CompilerInstance::ExecuteAction,
which is rare.

Fixes clangd/clangd#1745.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D158967

(cherry picked from commit e257c0a)

Author: zyn0217

clang-tools-extra/clangd/ClangdServer.cpp

@@ -34,6 +34,7 @@
 #include "support/MemoryTree.h"
 #include "support/ThreadsafeFS.h"
 #include "support/Trace.h"
+#include "clang/Basic/Stack.h"
 #include "clang/Format/Format.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Tooling/CompilationDatabase.h"
@@ -52,8 +53,8 @@
 #include <optional>
 #include <string>
 #include <type_traits>
-#include <vector>
 #include <utility>
+#include <vector>
 
 namespace clang {
 namespace clangd {
@@ -112,6 +113,7 @@ struct UpdateIndexCallbacks : public ParsingCallbacks {
                  FIndex(FIndex),
                  // shared_ptr extends lifetime
                  Stdlib(Stdlib)]() mutable {
+      clang::noteBottomOfStack();
       IndexFileIn IF;
       IF.Symbols = indexStandardLibrary(std::move(CI), Loc, *TFS);
       if (Stdlib->isBest(LO))

clang-tools-extra/clangd/TUScheduler.cpp

@@ -63,6 +63,7 @@
 #include "support/ThreadCrashReporter.h"
 #include "support/Threading.h"
 #include "support/Trace.h"
+#include "clang/Basic/Stack.h"
 #include "clang/Frontend/CompilerInvocation.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "llvm/ADT/FunctionExtras.h"
@@ -464,6 +465,10 @@ class PreambleThread {
   }
 
   void run() {
+    // We mark the current as the stack bottom so that clang running on this
+    // thread can notice the stack usage and prevent stack overflow with best
+    // efforts. Same applies to other calls thoughout clangd.
+    clang::noteBottomOfStack();
     while (true) {
       std::optional<PreambleThrottlerRequest> Throttle;
       {
@@ -1383,6 +1388,7 @@ void ASTWorker::startTask(llvm::StringRef Name,
 }
 
 void ASTWorker::run() {
+  clang::noteBottomOfStack();
   while (true) {
     {
       std::unique_lock<std::mutex> Lock(Mutex);
@@ -1777,6 +1783,7 @@ void TUScheduler::runWithPreamble(llvm::StringRef Name, PathRef File,
                Ctx = Context::current().derive(FileBeingProcessed,
                                                std::string(File)),
                Action = std::move(Action), this]() mutable {
+    clang::noteBottomOfStack();
     ThreadCrashReporter ScopedReporter([&Name, &Contents, &Command]() {
       llvm::errs() << "Signalled during preamble action: " << Name << "\n";
       crashDumpCompileCommand(llvm::errs(), Command);

clang-tools-extra/clangd/index/Background.cpp

@@ -30,6 +30,7 @@
 #include "support/Trace.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Basic/Stack.h"
 #include "clang/Frontend/FrontendAction.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseSet.h"
@@ -108,6 +109,7 @@ BackgroundIndex::BackgroundIndex(
   for (unsigned I = 0; I < Opts.ThreadPoolSize; ++I) {
     ThreadPool.runAsync("background-worker-" + llvm::Twine(I + 1),
                         [this, Ctx(Context::current().clone())]() mutable {
+                          clang::noteBottomOfStack();
                           WithContext BGContext(std::move(Ctx));
                           Queue.work([&] { Rebuilder.idle(); });
                         });

clang-tools-extra/clangd/test/infinite-instantiation.test

@@ -0,0 +1,13 @@
+// RUN: cp %s %t.cpp
+// RUN: not clangd -check=%t.cpp 2>&1 | FileCheck -strict-whitespace %s
+
+// CHECK: [template_recursion_depth_exceeded]
+
+template <typename... T>
+constexpr int f(T... args) {
+  return f(0, args...);
+}
+
+int main() {
+  auto i = f();
+}

clang-tools-extra/clangd/tool/ClangdMain.cpp

@@ -29,6 +29,7 @@
 #include "support/ThreadCrashReporter.h"
 #include "support/ThreadsafeFS.h"
 #include "support/Trace.h"
+#include "clang/Basic/Stack.h"
 #include "clang/Format/Format.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringRef.h"
@@ -710,6 +711,9 @@ enum class ErrorResultCode : int {
 };
 
 int clangdMain(int argc, char *argv[]) {
+  // Clang could run on the main thread. e.g., when the flag '-check' or '-sync'
+  // is enabled.
+  clang::noteBottomOfStack();
   llvm::InitializeAllTargetInfos();
   llvm::sys::PrintStackTraceOnErrorSignal(argv[0]);
   llvm::sys::AddSignalHandler(

clang/lib/Frontend/FrontendAction.cpp

@@ -15,6 +15,7 @@
 #include "clang/Basic/FileEntry.h"
 #include "clang/Basic/LangStandard.h"
 #include "clang/Basic/Sarif.h"
+#include "clang/Basic/Stack.h"
 #include "clang/Frontend/ASTUnit.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/FrontendDiagnostic.h"
@@ -1150,6 +1151,10 @@ void ASTFrontendAction::ExecuteAction() {
   CompilerInstance &CI = getCompilerInstance();
   if (!CI.hasPreprocessor())
     return;
+  // This is a fallback: If the client forgets to invoke this, we mark the
+  // current stack as the bottom. Though not optimal, this could help prevent
+  // stack overflow during deep recursion.
+  clang::noteBottomOfStack();
 
   // FIXME: Move the truncation aspect of this into Sema, we delayed this till
   // here so the source manager would be initialized.