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C++: Fix BMN issue with cpp/integer-multiplication-cast-to-long. #21457

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Merged
geoffw0 merged 6 commits into from
Mar 16, 2026
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C++: Fix BMN issue with cpp/integer-multiplication-cast-to-long. #21457

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da7da80
C++: Add pseudo-buildless test cases (some missing declarations).
geoffw0 Mar 10, 2026
00d8a10
C++: Add Function.hasAmbiguousReturnType.
geoffw0 Mar 11, 2026
6552c84
C++: Fix BMN issue in cpp/integer-multiplication-cast-to-long.
geoffw0 Mar 11, 2026
4a39055
C++: Change note.
geoffw0 Mar 11, 2026
2f7526d
C++: Clarify doc comment and make build-mode: nonereferences more con…
geoffw0 Mar 16, 2026
8df4dfb
C++: Autoformat.
geoffw0 Mar 16, 2026
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8 changes: 8 additions & 0 deletions cpp/ql/lib/semmle/code/cpp/Function.qll
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Expand Up @@ -524,6 +524,14 @@ class Function extends Declaration, ControlFlowNode, AccessHolder, @function {
not exists(NewOrNewArrayExpr new | e = new.getAllocatorCall().getArgument(0))
)
}

/**
* Holds if this function has ambiguous return type (this occurs sometimes in
* Build Mode None).
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Copilot AI Mar 11, 2026

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The doc comment is a bit unclear/grammatically off: consider “has an ambiguous return type” and clarify what “ambiguous” means here (for example, whether it includes functions with zero extracted return types as well as multiple). Also consider aligning capitalization/wording with existing comments that refer to “build mode none”.

Suggested change
* Holds if this function has ambiguous return type (this occurs sometimes in
* Build Mode None).
* Holds if this function has an ambiguous return type, meaning that zero or
* multiple return types were extracted (this can occur in build mode none).

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@jketema jketema Mar 12, 2026

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We might want to standardize this. In Compilation we use phrasing like "using the "none" build mode", and in the change notes we use build-mode: none.

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@geoffw0 geoffw0 Mar 16, 2026

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Yes. I don't feel qualified to pick something as standard, but I dislike the clunky phrasing "using the "none" build mode", so I'm going with build-mode: none. Updated.

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@jketema jketema Mar 16, 2026

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For the record: I think you're perfectly qualified.

*/
predicate hasAmbiguousReturnType() {
count(this.getType()) != 1
}
}

pragma[noinline]
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4 changes: 3 additions & 1 deletion cpp/ql/src/Likely Bugs/Arithmetic/IntMultToLong.ql
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Expand Up @@ -218,7 +218,9 @@ where
// only report if we cannot prove that the result of the
// multiplication will be less (resp. greater) than the
// maximum (resp. minimum) number we can compute.
overflows(me, t1)
overflows(me, t1) and
// exclude cases where the expression type may not have been extracted accurately
not me.getParent().(Call).getTarget().hasAmbiguousReturnType()
select me,
"Multiplication result may overflow '" + me.getType().toString() + "' before it is converted to '"
+ me.getFullyConverted().getType().toString() + "'."
4 changes: 4 additions & 0 deletions cpp/ql/src/change-notes/2026-03-11-integer-multiplication-cast-to-long.md
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@@ -0,0 +1,4 @@
---
category: minorAnalysis
---
* Fixed an issue with the "Multiplication result converted to larger type" (`cpp/integer-multiplication-cast-to-long`) query causing false positive results in Build Mode Node databases.
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28 changes: 28 additions & 0 deletions cpp/ql/test/query-tests/Likely Bugs/Arithmetic/IntMultToLong/Buildless.c
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@@ -0,0 +1,28 @@
// semmle-extractor-options: --expect_errors

void test_float_double1(float f, double d) {
float r1 = f * f; // GOOD
float r2 = f * d; // GOOD
double r3 = f * f; // BAD
double r4 = f * d; // GOOD

float f1 = fabsf(f * f); // GOOD
float f2 = fabsf(f * d); // GOOD
double f3 = fabs(f * f); // BAD [NOT DETECTED]
double f4 = fabs(f * d); // GOOD
}

double fabs(double f);
float fabsf(float f);

void test_float_double2(float f, double d) {
float r1 = f * f; // GOOD
float r2 = f * d; // GOOD
double r3 = f * f; // BAD
double r4 = f * d; // GOOD

float f1 = fabsf(f * f); // GOOD
float f2 = fabsf(f * d); // GOOD
double f3 = fabs(f * f); // BAD [NOT DETECTED]
double f4 = fabs(f * d); // GOOD
}
2 changes: 2 additions & 0 deletions cpp/ql/test/query-tests/Likely Bugs/Arithmetic/IntMultToLong/IntMultToLong.expected
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@@ -1,3 +1,5 @@
| Buildless.c:6:17:6:21 | ... * ... | Multiplication result may overflow 'float' before it is converted to 'double'. |
| Buildless.c:21:17:21:21 | ... * ... | Multiplication result may overflow 'float' before it is converted to 'double'. |
| IntMultToLong.c:4:10:4:14 | ... * ... | Multiplication result may overflow 'int' before it is converted to 'long long'. |
| IntMultToLong.c:7:16:7:20 | ... * ... | Multiplication result may overflow 'int' before it is converted to 'long long'. |
| IntMultToLong.c:18:19:18:23 | ... * ... | Multiplication result may overflow 'float' before it is converted to 'double'. |
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