[GitHub] [incubator-nuttx] patacongo removed a comment on issue #1263: pthread cleanup callbacks execute in user mode.

[GitBox <gi...@apache.org>]

patacongo removed a comment on issue #1263:
URL: https://github.com/apache/incubator-nuttx/issues/1263#issuecomment-645453760


   Other, related issues noted in the TODO list:
   
       Title:       ISSUES WITH atexit(), on_exit(), AND pthread_cleanup_pop()
       Description: These functions execute with the following bad properties:
   
                    1. They run with interrupts disabled,
                    2. They run in supervisor mode (if applicable), and
                    3. They do not obey any setup of PIC or address
                       environments. Do they need to?
                    4. In the case of task_delete() and pthread_cancel() without
                       deferred cancellation, these callbacks will run on the
                       thread of execution and address context of the caller of
                       task_delete() or pthread_cancel().  That is very bad!
   
                    The fix for all of these issues it to have the callbacks
                    run on the caller's thread as is currently done with
                    signal handlers.  Signals are delivered differently in
                    PROTECTED and KERNEL modes:  The delivery involves a
                    signal handling trampoline function in the user address
                    space and two signal handlers:  One to call the signal
                    handler trampoline in user mode (SYS_signal_handler) and
                    on in with the signal handler trampoline to return to
                    supervisor mode (SYS_signal_handler_return)
   
                    The primary difference is in the location of the signal
                    handling trampoline:
   
                    - In PROTECTED mode, there is on a single user space blob
                      with a header at the beginning of the block (at a well-
                      known location.  There is a pointer to the signal handler
                      trampoline function in that header.
                    - In the KERNEL mode, a special process signal handler
                      trampoline is used at a well-known location in every
                      process address space (ARCH_DATA_RESERVE->ar_sigtramp).
       Status:      Open
       Priority:    Medium Low.  This is an important change to some less
                    important interfaces.  For the average user, these
                    functions are just fine the way they are.
   


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