How to get stack bounds of current process?
lev at FreeBSD.org
Mon May 10 17:45:31 UTC 2010
You wrote 10 мая 2010 г., 18:58:17:
>> I'm proting some application from Linux, which discover its stack
>> bounds by reading and pasing "/proc/self/maps". FreeBSD have
>> "/prov/curproc/map", but I can not find how to determine which record
>> is for stack (I've looked into implementation of proc_fs, but it
>> doesn't contain any specail processing for process stack).
>> How could I determine stack bounds of current process on FreeBSD
> I think the right question is why the program needs the information at all.
> Really, the system has no data to answer your question. Which stack are
> you asking for ? The stack of main thread, set up by kernel, is very
> different from the stack established by the threading library for
> newly created thread. What should happen for signal altstacks ?
> Also, the threading library clips the main thread stack to match its
> size with default stack size (I do think this is unsafe and wrong).
It is port of new openjdk7 build. It adds function with
this comment in Linux-specific code (BSD port is based on Linux one):
// Linux uses a growable mapping for the stack, and if the mapping for
// the stack guard pages is not removed when we detach a thread the
// stack cannot grow beyond the pages where the stack guard was
// mapped. If at some point later in the process the stack expands to
// that point, the Bsd kernel cannot expand the stack any further
// because the guard pages are in the way, and a segfault occurs.
// However, it's essential not to split the stack region by unmapping
// a region (leaving a hole) that's already part of the stack mapping,
// so if the stack mapping has already grown beyond the guard pages at
// the time we create them, we have to truncate the stack mapping.
// So, we need to know the extent of the stack mapping when
// create_stack_guard_pages() is called.
// Find the bounds of the stack mapping. Return true for success.
// We only need this for stacks that are growable: at the time of
// writing thread stacks don't use growable mappings (i.e. those
// creeated with MAP_GROWSDOWN), and aren't marked "[stack]", so this
// only applies to the main thread.
// If the (growable) stack mapping already extends beyond the point
// where we're going to put our guard pages, truncate the mapping at
// that point by munmap()ping it. This ensures that when we later
// munmap() the guard pages we don't leave a hole in the stack
Solaris code simple map/unmap needed pages, and Linux port
checks stack region and applies special processing for growable stack
I'm not sure, should BSD port behaves as Linux or as Solaris one.
// Black Lion AKA Lev Serebryakov <lev at FreeBSD.org>
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