https://github.com/balazs-benics-sonarsource created
https://github.com/llvm/llvm-project/pull/156668
When calculating the offset of a FieldRegion, we need to find out which field
index the given field refers to.
Previously, if for some reason the field was not found, then the `Idx` passed
to `Layout.getFieldOffset` was out of bounds and caused undefined behavior when
dereferenced an out of bounds element in `ASTVector::FieldOffsets::operator[]`,
which asserts this in debug builds, but exposes the undefined behavior in
release builds.
In this patch, I refactored how we enumerate the fields, and gracefully handle
the scenario where the field is not found.
That case is still bad, but at least it should not expose the undefined
behavior in release builds, and should assert earlier in debug builds than
before.
The motivational case was transformed into a regression test, that would fail
if no canonicalization would happen when creating a FieldRegion. This was
reduced from a production crash.
In the test case, due to how modules work, there would be multiple copies of
the same template specialization in the AST. This could lead into inconsistent
state when the FieldRegion's Decl was different to the RecordDecl's field -
because one referred to the first and the other to the second. This made
`calculateOffset` fail to compute the field index, triggering the undefined
behavior in production.
While this inconsistency gets fixed now, I think the assertion is still
warranted to avoid potential undefined behavior in release builds.
CPP-6691,CPP-6849
Co-authored-by: Marco Borgeaud <marco.borge...@sonarsource.com>
From 5d776f7eec057c51e8d9346492b1d4f4128bd1be Mon Sep 17 00:00:00 2001
From: Balazs Benics <balazs.ben...@sonarsource.com>
Date: Wed, 3 Sep 2025 15:18:41 +0200
Subject: [PATCH] [analyzer] Canonicalize the Decls of FieldRegions
When calculating the offset of a FieldRegion, we need to find out which
field index the given field refers to.
Previously, if for some reason the field was not found, then the `Idx`
passed to `Layout.getFieldOffset` was out of bounds and caused undefined
behavior when dereferenced an out of bounds element in
`ASTVector::FieldOffsets::operator[]`, which asserts this in debug
builds, but exposes the undefined behavior in release builds.
In this patch, I refactored how we enumerate the fields, and gracefully
handle the scenario where the field is not found.
That case is still bad, but at least it should not expose the undefined
behavior in release builds, and should assert earlier in debug builds
than before.
The motivational case was transformed into a regression test, that would
fail if no canonicalization would happen when creating a FieldRegion.
This was reduced from a production crash.
In the test case, due to how modules work, there would be multiple
copies of the same template specialization in the AST.
This could lead into inconsistent state when the FieldRegion's Decl was
different to the RecordDecl's field - because one referred to the first
and the other to the second. This made `calculateOffset` fail to compute
the field index, triggering the undefined behavior in production.
While this inconsistency gets fixed now, I think the assertion is still
warranted to avoid potential undefined behavior in release builds.
CPP-6691,CPP-6849
Co-authored-by: Marco Borgeaud <marco.borge...@sonarsource.com>
---
clang/lib/StaticAnalyzer/Core/MemRegion.cpp | 23 +++++++-----
.../explicit-templ-inst-crash-in-modules.cppm | 35 +++++++++++++++++++
2 files changed, 50 insertions(+), 8 deletions(-)
create mode 100644
clang/test/Analysis/modules/explicit-templ-inst-crash-in-modules.cppm
diff --git a/clang/lib/StaticAnalyzer/Core/MemRegion.cpp
b/clang/lib/StaticAnalyzer/Core/MemRegion.cpp
index 5f271963e3d09..f68fb1e6df759 100644
--- a/clang/lib/StaticAnalyzer/Core/MemRegion.cpp
+++ b/clang/lib/StaticAnalyzer/Core/MemRegion.cpp
@@ -1271,7 +1271,7 @@ const SymbolicRegion
*MemRegionManager::getSymbolicHeapRegion(SymbolRef Sym) {
const FieldRegion*
MemRegionManager::getFieldRegion(const FieldDecl *d,
const SubRegion* superRegion){
- return getSubRegion<FieldRegion>(d, superRegion);
+ return getSubRegion<FieldRegion>(d->getCanonicalDecl(), superRegion);
}
const ObjCIvarRegion*
@@ -1704,16 +1704,23 @@ static RegionOffset calculateOffset(const MemRegion *R)
{
if (SymbolicOffsetBase)
continue;
- // Get the field number.
- unsigned idx = 0;
- for (RecordDecl::field_iterator FI = RD->field_begin(),
- FE = RD->field_end(); FI != FE; ++FI, ++idx) {
- if (FR->getDecl() == *FI)
- break;
+ auto MaybeFieldIdx = [FR, RD]() -> std::optional<unsigned> {
+ assert(FR->getDecl()->getCanonicalDecl() == FR->getDecl());
+ for (auto [Idx, Field] : llvm::enumerate(RD->fields())) {
+ if (FR->getDecl() == Field->getCanonicalDecl())
+ return Idx;
+ }
+ return std::nullopt;
+ }();
+
+ if (!MaybeFieldIdx.has_value()) {
+ assert(false && "Field not found");
+ goto Finish; // Invalid offset.
}
+
const ASTRecordLayout &Layout = R->getContext().getASTRecordLayout(RD);
// This is offset in bits.
- Offset += Layout.getFieldOffset(idx);
+ Offset += Layout.getFieldOffset(MaybeFieldIdx.value());
break;
}
}
diff --git
a/clang/test/Analysis/modules/explicit-templ-inst-crash-in-modules.cppm
b/clang/test/Analysis/modules/explicit-templ-inst-crash-in-modules.cppm
new file mode 100644
index 0000000000000..6eec29c7187ba
--- /dev/null
+++ b/clang/test/Analysis/modules/explicit-templ-inst-crash-in-modules.cppm
@@ -0,0 +1,35 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// DEFINE: %{common-flags}= -std=c++20 -I %t -fprebuilt-module-path=%t
+//
+// RUN: %clang_cc1 %{common-flags} %t/other.cppm -emit-module-interface -o
%t/other.pcm
+// RUN: %clang_analyze_cc1 -analyzer-checker=core %{common-flags}
%t/entry.cppm -verify
+
+
+//--- MyStruct.h
+template <typename T> struct MyStruct {
+ T data = 0;
+};
+template struct MyStruct<int>; // Explicit template instantiation.
+
+//--- other.cppm
+module;
+#include "MyStruct.h"
+export module other;
+static void implicit_instantiate_MyStruct() {
+ MyStruct<int> var;
+ (void)var;
+}
+
+//--- entry.cppm
+// expected-no-diagnostics
+module;
+#include "MyStruct.h"
+module other;
+
+void entry_point() {
+ MyStruct<int> var; // no-crash
+ (void)var;
+}
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