[flang] fix spurious runtime crash on TRIM('')
The standard interoperability routine CFI_establish() does not
accept a zero-length CHARACTER type. Since these can be valid
results of intrinsic function references, work around the design
of CFI_establish() in the wrapper routine that calls it.
Differential Revision: https://reviews.llvm.org/D99296
GitOrigin-RevId: d811c829af616fd0bec08c7bebbe946e9bc96eea
diff --git a/runtime/descriptor.cpp b/runtime/descriptor.cpp
index efcd61b..b66874b 100644
--- a/runtime/descriptor.cpp
+++ b/runtime/descriptor.cpp
@@ -31,9 +31,23 @@
int rank, const SubscriptValue *extent, ISO::CFI_attribute_t attribute,
bool addendum) {
Terminator terminator{__FILE__, __LINE__};
+ // Subtle: the standard CFI_establish() function doesn't allow a zero
+ // elem_len argument in cases where elem_len is not ignored; and when it
+ // returns an error code (CFI_INVALID_ELEM_LEN in this case), it must not
+ // modify the descriptor. That design makes sense, maybe, for actual
+ // C interoperability, but we need to work around it here. A zero
+ // incoming element length is replaced by 4 so that it will be valid
+ // for all CHARACTER kinds.
+ std::size_t workaroundElemLen{elementBytes ? elementBytes : 4};
RUNTIME_CHECK(terminator,
- ISO::CFI_establish(&raw_, p, attribute, t.raw(), elementBytes, rank,
+ ISO::CFI_establish(&raw_, p, attribute, t.raw(), workaroundElemLen, rank,
extent) == CFI_SUCCESS);
+ if (elementBytes == 0) {
+ raw_.elem_len = 0;
+ for (int j{0}; j < rank; ++j) {
+ GetDimension(j).SetByteStride(0);
+ }
+ }
raw_.f18Addendum = addendum;
DescriptorAddendum *a{Addendum()};
RUNTIME_CHECK(terminator, addendum == (a != nullptr));
