The motivating issue was the following:
```
$ cat main.cpp
enum class EnumVals : uint16_t {
VAL1 = 0
};
struct Foo {
EnumVals b1 : 4;
};
int main() {
// Assign value out-of-range if
// bit-field were signed
Foo f{.b1 = (EnumVals)8};
return 0; // Break here
}
(lldb) script
>>> lldb.frame.FindVariable("f").GetChildMemberWithName("b1").GetValueAsUnsigned()
4294967288
```
In the above example we observe a unsigned integer wrap-around
because we sign-extended the bit-fields underlying Scalar value
before casting it to an unsigned. The sign extension occurs because
we don't mark APSInt::IsUnsigned == true correctly when extracting
the value from memory (in Value::ResolveValue). The reason why sign
extension causes the wraparound is that the value we're assigning
to the bit-field is out-of-range (if it were a signed bit-field),
which causes `Scalar::sext` to left-fill the Scalar with 1s.
This patch corrects GetEncoding to account for unsigned enum types.
With this change the Scalar would be zero-extended instead.
This is mainly a convenience fix which well-formed code wouldn't
encounter.
rdar://
99785324
Differential Revision: https://reviews.llvm.org/D134493
case clang::Type::Record:
break;
case clang::Type::Enum:
- return lldb::eEncodingSint;
+ return qual_type->isUnsignedIntegerOrEnumerationType()
+ ? lldb::eEncodingUint
+ : lldb::eEncodingSint;
case clang::Type::DependentSizedArray:
case clang::Type::DependentSizedExtVector:
case clang::Type::UnresolvedUsing:
--- /dev/null
+"""
+Test that SBValue doesn't incorrectly sign-extend
+the Scalar value of a bitfield that has an unsigned
+enum type.
+
+We test this by assigning to a bit-field a value
+that is out-of-range of it's signed counterpart.
+I.e., with a bit-field of width 4, assigning
+8 to it would be out-of-range if we treated it
+as a signed. If LLDB were to sign-extend the Scalar
+(which shouldn't happen for unsigned bit-fields)
+it would left-fill the result with 1s; we test
+for this not to happen.
+"""
+
+import lldbsuite.test.lldbinline as lldbinline
+
+lldbinline.MakeInlineTest(__file__, globals())
--- /dev/null
+#include <stdint.h>
+
+enum class EnumVals : uint16_t { VAL0 = 0 };
+
+struct Foo {
+ EnumVals b : 4;
+};
+
+int main(int argc, char const *argv[], char const *envp[]) {
+ Foo f{.b = static_cast<EnumVals>(8)};
+ return 0; //% b = self.frame().FindVariable("f").GetChildMemberWithName("b")
+ //% val = b.GetValueAsUnsigned()
+ //% self.assertEqual(val, 8, "Bit-field not correctly extracted")
+}