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MACH_RCV_INVALID_TRAILER
The requested receive trailer is not a supported combination
MACH_RCV_INVALID_TRAILER is a receive-option error. XNU defines trailer type and element selection through the MACH_RCV_TRAILER_TYPE and MACH_RCV_TRAILER_ELEMENTS masks. The status means the requested trailer type or number of elements is not supported; it does not mean that an arbitrary sender appended corrupt bytes to the message.
Trailers can carry metadata such as a sequence number, sender security information, audit data, context, or access-vector information. Requesting more metadata changes the storage requirement and the compatibility assumptions of the receiver. Code that hard-codes a numeric option mask can silently ask for an unsupported combination after an SDK or binding change.
What to inspect
- Build trailer options with the named macros and retain the decoded mask in diagnostics.
- Verify that the receive buffer accounts for the trailer size selected by the option mask.
- Request only the trailer elements that the receiver actually consumes, then validate their documented structure before use.
- Do not confuse this receive request error with
MACH_SEND_INVALID_TRAILER, which concerns a sender-provided trailer.
References
- Apple XNU source: mach/message.h
- Mach Kernel Interface Reference: mach_msg
- GNU Mach Reference Manual: interprocess communication
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