Need help on l4_msgtag_has_error

Chen Tian chen.tian at
Thu Dec 8 00:56:59 CET 2011


Can some one tell me when a msg tag is set to the error code i.e., tag
= 0x8000 ?

I have a parent thread A, which creates a child thread B, and thread C
is assigned as B's pager and exception handler.

When thread A destroys B via l4_task_unmap, thread C is invoked and
the tag returned from ipc_reply_and_wait cannot pass
l4_msgtag_has_error check. This is very weird. When B dies, will it
generate some sort of exceptions which will cause C to be invoked?

If I ask thread C to ignore this IPC message, it seems fine because
thread B is anyway destroyed. But I am still wondering if I did
something logically wrong or the tag error can be safely ignored,
especially in the situation I described above?



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