From 29ac3a5b822ba8c097a3ae78d983cdb94da43dd4 Mon Sep 17 00:00:00 2001
From: Julian Lettner <jlettner@apple.com>
Date: Mon, 4 Feb 2019 22:06:30 +0000
Subject: [PATCH] [SanitizerCoverage] Clang crashes if user declares
 `__sancov_lowest_stack` variable

Summary:
If the user declares or defines `__sancov_lowest_stack` with an
unexpected type, then `getOrInsertGlobal` inserts a bitcast and the
following cast fails:
```
Constant *SanCovLowestStackConstant =
       M.getOrInsertGlobal(SanCovLowestStackName, IntptrTy);
SanCovLowestStack = cast<GlobalVariable>(SanCovLowestStackConstant);
```

This variable is a SanitizerCoverage implementation detail and the user
should generally never have a need to access it, so we emit an error
now.

rdar://problem/44143130

Reviewers: morehouse

Differential Revision: https://reviews.llvm.org/D57633

llvm-svn: 353100
---
 .../Transforms/Instrumentation/SanitizerCoverage.cpp |  7 ++++++-
 .../stack-depth-variable-declared-by-user.ll         | 12 ++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/Instrumentation/SanitizerCoverage/stack-depth-variable-declared-by-user.ll

diff --git a/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp b/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
index 18c6ceb3331f..21ad41c47f63 100644
--- a/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
+++ b/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
@@ -377,7 +377,12 @@ bool SanitizerCoverageModule::runOnModule(Module &M) {
 
   Constant *SanCovLowestStackConstant =
       M.getOrInsertGlobal(SanCovLowestStackName, IntptrTy);
-  SanCovLowestStack = cast<GlobalVariable>(SanCovLowestStackConstant);
+  SanCovLowestStack = dyn_cast<GlobalVariable>(SanCovLowestStackConstant);
+  if (!SanCovLowestStack) {
+    C->emitError(StringRef("'") + SanCovLowestStackName +
+                 "' should not be declared by the user");
+    return true;
+  }
   SanCovLowestStack->setThreadLocalMode(
       GlobalValue::ThreadLocalMode::InitialExecTLSModel);
   if (Options.StackDepth && !SanCovLowestStack->isDeclaration())
diff --git a/llvm/test/Instrumentation/SanitizerCoverage/stack-depth-variable-declared-by-user.ll b/llvm/test/Instrumentation/SanitizerCoverage/stack-depth-variable-declared-by-user.ll
new file mode 100644
index 000000000000..1ad96f82a694
--- /dev/null
+++ b/llvm/test/Instrumentation/SanitizerCoverage/stack-depth-variable-declared-by-user.ll
@@ -0,0 +1,12 @@
+; Ensure that we terminate with a useful error message (instead of crash) if the
+; user declares `__sancov_lowest_stack` with an unexpected type.
+; RUN: not opt < %s -sancov -sanitizer-coverage-level=1 \
+; RUN:         -sanitizer-coverage-stack-depth -S 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Wrong type: i32 instead of expected i64
+@__sancov_lowest_stack = thread_local global i32 0
+
+; CHECK: error: '__sancov_lowest_stack' should not be declared by the user
-- 
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