[PATCH/RFC] ARM: add a vma entry for the user accessible vector page

[Russell King - ARM Linux]

On Tue, Sep 14, 2010 at 01:24:04AM -0400, Nicolas Pitre wrote:
>     
> The kernel makes the high vector page visible to user space. This page
> contains (amongst others) small code segments that can be executed in
> user space.  Make this page visible through ptrace and /proc/<pid>/mem
> in order to let gdb perform code parsing needed for proper unwinding.
> 
> For example, the ERESTART_RESTARTBLOCK handler actually has a stack
> frame -- it returns to a PC value stored on the user's stack.   To
> unwind after a "sleep" system call was interrupted twice, GDB would
> have to recognize this situation and understand that stack frame
> layout -- which it currently cannot do.
> 
> We could fix this by hard-coding addresses in the vector page range into
> GDB, but that isn't really portable as not all of those addresses are
> guaranteed to remain stable across kernel releases.  And having the gdb
> process make an exception for this page and get  content from its own
> view of it looks strange, and it is not future proof either.

What if someone calls munmap() (or one of the other mmap calls) on
this vma?