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[flang][runtime] Detect byte order reversal problems #129093

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Merged
merged 1 commit into from
Feb 28, 2025
Merged

[flang][runtime] Detect byte order reversal problems #129093

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48 changes: 36 additions & 12 deletions flang-rt/lib/runtime/unit.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -511,7 +511,7 @@ void ExternalFileUnit::EndIoStatement() {
void ExternalFileUnit::BeginSequentialVariableUnformattedInputRecord(
IoErrorHandler &handler) {
RUNTIME_CHECK(handler, access == Access::Sequential);
std::int32_t header{0}, footer{0};
std::uint32_t header{0}, footer{0};
std::size_t need{recordOffsetInFrame_ + sizeof header};
std::size_t got{ReadFrame(frameOffsetInFile_, need, handler)};
// Try to emit informative errors to help debug corrupted files.
Expand All @@ -528,17 +528,41 @@ void ExternalFileUnit::BeginSequentialVariableUnformattedInputRecord(
recordLength = sizeof header + header; // does not include footer
need = recordOffsetInFrame_ + *recordLength + sizeof footer;
got = ReadFrame(frameOffsetInFile_, need, handler);
if (got < need) {
if (got >= need) {
footer = ReadHeaderOrFooter(recordOffsetInFrame_ + *recordLength);
}
if (frameOffsetInFile_ == 0 && recordOffsetInFrame_ == 0 &&
(got < need || footer != header)) {
// Maybe an omitted or incorrect byte swap flag setting?
// Try it the other way, since this is the first record.
// (N.B. Won't work on files starting with empty records, but there's
// no good way to know later if all preceding records were empty.)
swapEndianness_ = !swapEndianness_;
std::uint32_t header2{ReadHeaderOrFooter(0)};
std::size_t recordLength2{sizeof header2 + header2};
std::size_t need2{recordLength2 + sizeof footer};
std::size_t got2{ReadFrame(0, need2, handler)};
if (got2 >= need2) {
std::uint32_t footer2{ReadHeaderOrFooter(recordLength2)};
if (footer2 == header2) {
error = "Unformatted variable-length sequential file input "
"failed on the first record, probably due to a need "
"for byte order data conversion; consider adding "
"CONVERT='SWAP' to the OPEN statement or adding "
"FORT_CONVERT=SWAP to the execution environment";
}
}
swapEndianness_ = !swapEndianness_;
}
if (error) {
} else if (got < need) {
error = "Unformatted variable-length sequential file input failed at "
"record #%jd (file offset %jd): hit EOF reading record with "
"length %jd bytes";
} else {
footer = ReadHeaderOrFooter(recordOffsetInFrame_ + *recordLength);
if (footer != header) {
error = "Unformatted variable-length sequential file input failed at "
"record #%jd (file offset %jd): record header has length %jd "
"that does not match record footer (%jd)";
}
} else if (footer != header) {
error = "Unformatted variable-length sequential file input failed at "
"record #%jd (file offset %jd): record header has length %jd "
"that does not match record footer (%jd)";
}
}
if (error) {
Expand Down Expand Up @@ -590,7 +614,7 @@ void ExternalFileUnit::BackspaceFixedRecord(IoErrorHandler &handler) {

void ExternalFileUnit::BackspaceVariableUnformattedRecord(
IoErrorHandler &handler) {
std::int32_t header{0};
std::uint32_t header{0};
auto headerBytes{static_cast<std::int64_t>(sizeof header)};
frameOffsetInFile_ += recordOffsetInFrame_;
recordOffsetInFrame_ = 0;
Expand Down Expand Up @@ -775,8 +799,8 @@ void ExternalFileUnit::PopChildIo(ChildIo &child) {
child_.reset(child.AcquirePrevious().release()); // deletes top child
}

std::int32_t ExternalFileUnit::ReadHeaderOrFooter(std::int64_t frameOffset) {
std::int32_t word;
std::uint32_t ExternalFileUnit::ReadHeaderOrFooter(std::int64_t frameOffset) {
std::uint32_t word;
char *wordPtr{reinterpret_cast<char *>(&word)};
std::memcpy(wordPtr, Frame() + frameOffset, sizeof word);
if (swapEndianness_) {
Expand Down
2 changes: 1 addition & 1 deletion flang-rt/lib/runtime/unit.h
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Original file line number Diff line number Diff line change
Expand Up @@ -210,7 +210,7 @@ class ExternalFileUnit : public ConnectionState,
RT_API_ATTRS void CommitWrites();
RT_API_ATTRS bool CheckDirectAccess(IoErrorHandler &);
RT_API_ATTRS void HitEndOnRead(IoErrorHandler &);
RT_API_ATTRS std::int32_t ReadHeaderOrFooter(std::int64_t frameOffset);
RT_API_ATTRS std::uint32_t ReadHeaderOrFooter(std::int64_t frameOffset);

Lock lock_;

Expand Down