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[CHERI CSA] When inferring the alignment of the first field in a struct, use the alignment of the struct itself to help infer higher alignment. #203

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Merged
merged 1 commit into from
Jul 28, 2025
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[CHERI CSA] When inferring the alignment of the first field in a struct, use the alignment of the struct itself to help infer higher alignment. #203

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14 changes: 14 additions & 0 deletions clang/lib/StaticAnalyzer/Checkers/PointerAlignmentChecker.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -190,6 +190,20 @@ int getTrailingZerosCount(const MemRegion *R, ProgramStateRef State,
return -1;
unsigned NaturalAlign = ASTCtx.getTypeAlignInChars(PT).getQuantity();

if (const FieldRegion *FR = R->getAs<FieldRegion>()) {
// If this is the first field of a larger struct, we can use the alignment
// of the containing struct try to increase the assumed alignment.
const RegionOffset &Offset = FR->getAsOffset();
if (!Offset.hasSymbolicOffset() && Offset.getOffset() == 0) {
if (const auto *Base =
FR->getSuperRegion()->getAs<TypedValueRegion>()) {
auto BaseTy = Base->getValueType();
unsigned BaseAlign = ASTCtx.getTypeAlignInChars(BaseTy).getQuantity();
NaturalAlign = std::max(NaturalAlign, BaseAlign);
}
}
}

if (const ElementRegion *ER = R->getAs<ElementRegion>()) {
int ElTyTZ = APSInt::getUnsigned(NaturalAlign).countTrailingZeros();

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12 changes: 12 additions & 0 deletions clang/test/Analysis/pointer-alignment.c
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Expand Up @@ -202,3 +202,15 @@ void cast_and_assign(void) {
// no duplicate assign warn
*i = 42;
}

// ----
struct __attribute__((aligned(8))) AlignedParentStruct {
int a;
int b;
};

void write_to_first_member(struct AlignedParentStruct *chunk) {
// No warning because alignment of is inferred from the parent struct.
*(long long*)(&chunk->a) = 0;
}