Thanks for the review. You were right that the bug is in wchar_iterator; the backtrace confirms it. On 64-bit AIX, wchar_t is 4 bytes wide, so the iterator is constructed with m_width = 4. When the target-wide charset is UTF-16, set_be_le_names resolves it to UTF-16BE, which uses 2-byte code units. In this case, iconv returns EILSEQ after consuming only 2 bytes, but the existing code still does:

m_input += m_width;   /* advances by 4 */

m_bytes -= m_width;   /* m_bytes was 4, wraps to a huge size_t */

The subsequent while (m_bytes > 0) loop then continues past the end of the buffer, eventually corrupting the stack and crashing inside libiconv's qsort. I will send a v3 that addresses this issue directly.