Fix use-of-uninitialized-value in formatDateTime#96133
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alexey-milovidov merged 2 commits intomasterfrom Feb 6, 2026
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Fix use-of-uninitialized-value in formatDateTime#96133alexey-milovidov merged 2 commits intomasterfrom
formatDateTime#96133alexey-milovidov merged 2 commits intomasterfrom
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`mysqlFractionalSecondScaleNumDigits` and `mysqlFractionalSecondSingleZero` used `dest[i-1] += fractional_second % 10` which reads the destination byte before writing. When the output buffer is not pre-filled with the template (variable-width formatters path, e.g. format string contains `%M`), this reads uninitialized memory. Also fix `jodaFractionOfSecond` where `toString(fractional_second)` does not preserve leading zeros (e.g. fractional_second=5, scale=3 gives "5" instead of "005"), leaving the buffer partially uninitialized. Report: https://s3.amazonaws.com/clickhouse-test-reports/json.html?REF=master&sha=172a57f2ad219399818d551a89e2d32d62f88ccf&name_0=MasterCI&name_1=Stress%20test%20%28azure%2C%20amd_msan%29 Co-Authored-By: Claude Opus 4.6 <[email protected]>
Co-Authored-By: Claude Opus 4.6 <[email protected]>
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Backport #96133 to 26.1: Fix use-of-uninitialized-value in `formatDateTime`
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Backport #96133 to 25.11: Fix use-of-uninitialized-value in `formatDateTime`
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Backport #96133 to 25.12: Fix use-of-uninitialized-value in `formatDateTime`
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Backport #96133 to 25.8: Fix use-of-uninitialized-value in `formatDateTime`
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Backport #96133 to 25.3: Fix use-of-uninitialized-value in `formatDateTime`
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mysqlFractionalSecondScaleNumDigitsandmysqlFractionalSecondSingleZerouseddest[i-1] += fractional_second % 10which reads the destination byte before writing. When the output buffer is not pre-filled with the template (variable-width formatters path, e.g. format string contains%M), this reads uninitialized memory.Also fix
jodaFractionOfSecondwheretoString(fractional_second)does not preserve leading zeros (e.g. fractional_second=5, scale=3 gives "5" instead of "005"), leaving the buffer partially uninitialized.Report: https://s3.amazonaws.com/clickhouse-test-reports/json.html?REF=master&sha=172a57f2ad219399818d551a89e2d32d62f88ccf&name_0=MasterCI&name_1=Stress%20test%20%28azure%2C%20amd_msan%29
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Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):
Fix use-of-uninitialized-value in
formatDateTimewith non-fixed-width formatters, such as MySQL and JODA-style.