From a00328cd78bf4243dde3e8f11b1bd4fa1ea79b63 Mon Sep 17 00:00:00 2001
From: Boaz Brickner <brickner@google.com>
Date: Mon, 14 Oct 2024 14:06:50 +0200
Subject: [PATCH] [clang] Fix segmentation fault caused by stack overflow on
 deeply nested expressions (#111701)

Done by calling clang::runWithSufficientStackSpace().
Added CodeGenModule::runWithSufficientStackSpace() method similar to the
one in Sema to provide a single warning when this triggers
Fixes: #111699
---
 clang/lib/CodeGen/CGExpr.cpp        |  7 ++++++-
 clang/lib/CodeGen/CodeGenModule.cpp | 14 ++++++++++++++
 clang/lib/CodeGen/CodeGenModule.h   | 11 +++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index ec54da0a5b25714..1e8ffb53b53a09e 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -1528,7 +1528,12 @@ LValue CodeGenFunction::EmitCheckedLValue(const Expr *E, TypeCheckKind TCK) {
 ///
 LValue CodeGenFunction::EmitLValue(const Expr *E,
                                    KnownNonNull_t IsKnownNonNull) {
-  LValue LV = EmitLValueHelper(E, IsKnownNonNull);
+  // Running with sufficient stack space to avoid deeply nested expressions
+  // cause a stack overflow.
+  LValue LV;
+  CGM.runWithSufficientStackSpace(
+      E->getExprLoc(), [&] { LV = EmitLValueHelper(E, IsKnownNonNull); });
+
   if (IsKnownNonNull && !LV.isKnownNonNull())
     LV.setKnownNonNull();
   return LV;
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 7f0e0de61e477bc..b05ab3606a698ba 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -44,6 +44,7 @@
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/Module.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Basic/Stack.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/Version.h"
 #include "clang/CodeGen/BackendUtil.h"
@@ -1593,6 +1594,19 @@ void CodeGenModule::ErrorUnsupported(const Decl *D, const char *Type) {
   getDiags().Report(Context.getFullLoc(D->getLocation()), DiagID) << Msg;
 }
 
+void CodeGenModule::warnStackExhausted(SourceLocation Loc) {
+  // Only warn about this once.
+  if (!WarnedStackExhausted) {
+    getDiags().Report(Loc, diag::warn_stack_exhausted);
+    WarnedStackExhausted = true;
+  }
+}
+
+void CodeGenModule::runWithSufficientStackSpace(SourceLocation Loc,
+                                                llvm::function_ref<void()> Fn) {
+  clang::runWithSufficientStackSpace([&] { warnStackExhausted(Loc); }, Fn);
+}
+
 llvm::ConstantInt *CodeGenModule::getSize(CharUnits size) {
   return llvm::ConstantInt::get(SizeTy, size.getQuantity());
 }
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index c58bb88035ca8ab..57e06cbfac13a90 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -336,6 +336,7 @@ class CodeGenModule : public CodeGenTypeCache {
   std::unique_ptr<llvm::IndexedInstrProfReader> PGOReader;
   InstrProfStats PGOStats;
   std::unique_ptr<llvm::SanitizerStatReport> SanStats;
+  bool WarnedStackExhausted = false;
 
   // A set of references that have only been seen via a weakref so far. This is
   // used to remove the weak of the reference if we ever see a direct reference
@@ -1297,6 +1298,16 @@ class CodeGenModule : public CodeGenTypeCache {
   /// Print out an error that codegen doesn't support the specified decl yet.
   void ErrorUnsupported(const Decl *D, const char *Type);
 
+  /// Warn that the stack is nearly exhausted.
+  void warnStackExhausted(SourceLocation Loc);
+
+  /// Run some code with "sufficient" stack space. (Currently, at least 256K is
+  /// guaranteed). Produces a warning if we're low on stack space and allocates
+  /// more in that case. Use this in code that may recurse deeply to avoid stack
+  /// overflow.
+  void runWithSufficientStackSpace(SourceLocation Loc,
+                                   llvm::function_ref<void()> Fn);
+
   /// Set the attributes on the LLVM function for the given decl and function
   /// info. This applies attributes necessary for handling the ABI as well as
   /// user specified attributes like section.