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path: root/src/mman/mmap.c
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2015-04-10redesign and simplify vmlock systemRich Felker-6/+3
this global lock allows certain unlock-type primitives to exclude mmap/munmap operations which could change the identity of virtual addresses while references to them still exist. the original design mistakenly assumed mmap/munmap would conversely need to exclude the same operations which exclude mmap/munmap, so the vmlock was implemented as a sort of 'symmetric recursive rwlock'. this turned out to be unnecessary. commit 25d12fc0fc51f1fae0f85b4649a6463eb805aa8f already shortened the interval during which mmap/munmap held their side of the lock, but left the inappropriate lock design and some inefficiency. the new design uses a separate function, __vm_wait, which does not hold any lock itself and only waits for lock users which were already present when it was called to release the lock. this is sufficient because of the way operations that need to be excluded are sequenced: the "unlock-type" operations using the vmlock need only block mmap/munmap operations that are precipitated by (and thus sequenced after) the atomic-unlock they perform while holding the vmlock. this allows for a spectacular lack of synchronization in the __vm_wait function itself.
2014-08-16optimize locking against vm changes for mmap/munmapRich Felker-7/+6
the whole point of this locking is to prevent munmap, or mmap with MAP_FIXED, from deallocating virtual addresses, or changing the backing a given virtual address refers to, during certain race windows involving self-synchronized unmapping or destruction of pthread synchronization objects. there is no need for exclusion in the other direction, so it suffices to take the lock momentarily and release it before making the syscall, rather than holding it across the syscall.
2014-07-30add framework for mmap2 syscall unit to vary by archRich Felker-2/+3
2013-06-27disallow creation of objects larger than PTRDIFF_MAX via mmapRich Felker-0/+5
internally, other parts of the library assume sizes don't overflow ssize_t and/or ptrdiff_t, and the way this assumption is made valid is by preventing creating of such large objects. malloc already does so, but the check was missing from mmap. this is also a quality of implementation issue: even if the implementation internally could handle such objects, applications could inadvertently invoke undefined behavior by subtracting pointers within an object. it is very difficult to guard against this in applications, so a good implementation should simply ensure that it does not happen.
2012-12-20clean up and fix logic for making mmap fail on invalid/unsupported offsetsRich Felker-3/+7
the previous logic was assuming the kernel would give EINVAL when passed an invalid address, but instead with MAP_FIXED it was giving EPERM, as it considered this an attempt to map over kernel memory. instead of trying to get the kernel to do the rigth thing, the new code just handles the error in userspace. I have also cleaned up the code to use a single mask to check for invalid low bits and unsupported high bits, so it's simpler and more clearly correct. the old code was actually wrong for sizeof(long) smaller than sizeof(off_t) but not equal to 4; now it should be correct for all possibilities. for 64-bit systems, the low-bits test is new and extraneous (the kernel should catch the error anyway when the mmap2 syscall is not used), but it's cheap anyway. if this is an issue, the OFF_MASK definition could be tweaked to omit the low bits when SYS_mmap2 is not defined.
2011-09-27process-shared barrier support, based on discussion with bdonlanRich Felker-2/+11
this implementation is rather heavy-weight, but it's the first solution i've found that's actually correct. all waiters actually wait twice at the barrier so that they can synchronize exit, and they hold a "vm lock" that prevents changes to virtual memory mappings (and blocks pthread_barrier_destroy) until all waiters are finished inspecting the barrier. thus, it is safe for any thread to destroy and/or unmap the barrier's memory as soon as pthread_barrier_wait returns, without further synchronization.
2011-04-06consistency: change all remaining syscalls to use SYS_ rather than __NR_ prefixRich Felker-1/+1
2011-03-20global cleanup to use the new syscall interfaceRich Felker-2/+2
2011-02-13cleaning up syscalls in preparation for x86_64 portRich Felker-0/+4
- hide all the legacy xxxxxx32 name cruft in syscall.h so the actual source files can be clean and uniform across all archs. - cleanup llseek/lseek and mmap2/mmap handling for 32/64 bit systems - alternate implementation for nice if the target lacks nice syscall
2011-02-12initial check-in, version 0.5.0v0.5.0Rich Felker-0/+18