Need help on l4_msgtag_has_error

Adam Lackorzynski adam at
Fri Dec 9 00:14:48 CET 2011

On Wed Dec 07, 2011 at 15:56:59 -0800, Chen Tian wrote:
> 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?

Which error code does l4_error() return?

Adam                 adam at

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