With glibc and optimization, <stdio.h> turns getc_unlocked into an extern
inline function that reads the stdio buffer (fp->_IO_read_ptr) directly.
glibc, which is not instrumented, fills that buffer, so MemorySanitizer
treats the bytes as uninitialized and reports a false positive when the
parsers read from a FILE* (e.g., the fuzz harness FILE* leg, OSS-Fuzz
575915982). std::fgetc is an opaque call whose result MemorySanitizer treats
as initialized.
Select JSON_UNLOCKED_FILE_IO 0 when compiled with MemorySanitizer. This is a
regression from #5828 and not part of any release.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann
08d7fbb0a1