[PATCH] D77168: Add a flag to debug automatic variable initialization

[Jian Cai via Phabricator via cfe-commits]

jcai19 created this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

Add -ftrivial-auto-var-init-stop-after= to limit the number of times
stack variables are initialized when -ftrivial-auto-var-init= is used to
initialize stack variables to zero or a pattern. This flag can be used
to bisect uninitialized uses of a stack variable exposed by automatic
variable initialization, such as http://crrev.com/c/2020401.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D77168

Files:
  clang/include/clang/Basic/LangOptions.def
  clang/include/clang/Driver/Options.td
  clang/lib/CodeGen/CGDecl.cpp
  clang/lib/Driver/ToolChains/Clang.cpp
  clang/lib/Frontend/CompilerInvocation.cpp


Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -3273,6 +3273,11 @@
       Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args) << Val;
   }
 
+  if (Arg *A = Args.getLastArg(OPT_ftrivial_auto_var_init_stop_after)) {
+    unsigned Val = (unsigned)std::stoi(A->getValue());
+    Opts.TrivialAutoVarInitStopAfter = Val;
+  }
+
   // Parse -fsanitize= arguments.
   parseSanitizerKinds("-fsanitize=", Args.getAllArgValues(OPT_fsanitize_EQ),
                       Diags, Opts.Sanitize);
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -3088,6 +3088,13 @@
     CmdArgs.push_back(
         Args.MakeArgString("-ftrivial-auto-var-init=" + TrivialAutoVarInit));
   }
+
+  if (Arg *A = Args.getLastArg(options::OPT_ftrivial_auto_var_init_stop_after)) {
+    A->claim();
+    StringRef Val = A->getValue();
+    CmdArgs.push_back(
+        Args.MakeArgString("-ftrivial-auto-var-init-stop-after=" + Val));
+  }
 }
 
 static void RenderOpenCLOptions(const ArgList &Args, ArgStringList &CmdArgs) {
Index: clang/lib/CodeGen/CGDecl.cpp
===================================================================
--- clang/lib/CodeGen/CGDecl.cpp
+++ clang/lib/CodeGen/CGDecl.cpp
@@ -1809,6 +1809,19 @@
         LangOptions::TrivialAutoVarInitKind::Uninitialized)
       return;
 
+    unsigned StopAfter = getContext().getLangOpts().TrivialAutoVarInitStopAfter;
+    if (StopAfter) {
+      static unsigned Counter = 0;
+      if (Counter >= StopAfter)
+        return;
+      if (Counter++ == StopAfter - 1) {
+        const DeclContext * CD = D.getParentFunctionOrMethod ();
+        std::string FunctionName = (cast<FunctionDecl>(CD))->getNameInfo().getAsString();
+        StringRef SourceFileName = CGM.getModule().getSourceFileName();
+        llvm::errs() << "The last variable initialized is " << D.getName() << " of function " << FunctionName << " in " << SourceFileName << "\n";
+      }
+    }
+
     // Only initialize a __block's storage: we always initialize the header.
     if (emission.IsEscapingByRef && !locIsByrefHeader)
       Loc = emitBlockByrefAddress(Loc, &D, /*follow=*/false);
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -1799,6 +1799,8 @@
 def enable_trivial_var_init_zero : Flag<["-"], "enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang">,
   Flags<[CC1Option, CoreOption]>,
   HelpText<"Trivial automatic variable initialization to zero is only here for benchmarks, it'll eventually be removed, and I'm OK with that because I'm only using it to benchmark">;
+def ftrivial_auto_var_init_stop_after : Joined<["-"], "ftrivial-auto-var-init-stop-after=">, Group<f_Group>,
+  Flags<[CC1Option, CoreOption]>, HelpText<"Stop initializing trivial automatic stack variables after the specified number of instances">;
 def fstandalone_debug : Flag<["-"], "fstandalone-debug">, Group<f_Group>, Flags<[CoreOption]>,
   HelpText<"Emit full debug info for all types used by the program">;
 def fno_standalone_debug : Flag<["-"], "fno-standalone-debug">, Group<f_Group>, Flags<[CoreOption]>,
Index: clang/include/clang/Basic/LangOptions.def
===================================================================
--- clang/include/clang/Basic/LangOptions.def
+++ clang/include/clang/Basic/LangOptions.def
@@ -293,6 +293,8 @@
              "stack protector mode")
 ENUM_LANGOPT(TrivialAutoVarInit, TrivialAutoVarInitKind, 2, TrivialAutoVarInitKind::Uninitialized,
              "trivial automatic variable initialization")
+VALUE_LANGOPT(TrivialAutoVarInitStopAfter, 32, 0,
+             "stop trivial automatic variable initialization after the specified number of instances")
 ENUM_LANGOPT(SignedOverflowBehavior, SignedOverflowBehaviorTy, 2, SOB_Undefined,
              "signed integer overflow handling")
 


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