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They're surprisingly expensive to look up.
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The existing view-specific state was stored in several global unordered
maps. Many of these were accessed without locking, including
`viewSpecificMutexes`, which is racy in the face of multiple threads.
View-specific state is stored in a new heap-allocated
`ViewSpecificState` struct that is reference counted via
`std::shared_ptr`. A static map holds a `std::weak_ptr` to each
view-specific state, keyed by session id. `SharedCache` retrieves its
view-specific state during its constructor.
Since `ViewSpecificState` is reference counted it will naturally be
deallocated when the last `SharedCache` instance that references it goes
away. Its corresponding entry will remain in the static map, though
since it only holds a `std::weak_ptr` rather than any state it will not
use much memory. The next time view-specific state is retrieved any
expired entries will be removed from the map.
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`BNDSCViewGetAllImages`
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A problem with processing Objective-C sections at the time a library is loaded is that some of the references within those sections may refer to unload sections. This results in things like selectors not being correctly typed and named.
This commit provides a way for users to manually trigger Objective-C parsing against sections for a specific library or all libraries, via the API. Combined with the previous commit a user can use the API to batch load a number of libraries and skip Objective-C processing for each one and then run it across the entire of the DSC once they are all loaded.
Further improvement would be to provide a way to trigger Objective-C processing through the UI.
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library
This is useful when batch loading libraries to avoid extra processing (once the next commit has landed).
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Prior to this commit the function `DSCObjCProcessor::PostProcessObjCSections` never does anything because it doesn't use the correct names to get the Objective-C sections of the recently loaded library. In fact it never does anything because the DSC never has sections with the names its searching for.
This commit passes the `baseName` (the name of the library that was loaded), which is what other Objective-C section processing code does. Combining the base name with the section names it will now find them and process them as intended. This was resulting in alot of Objective-C related stuff being missed.
There is however still an issue of the fact that the way this DSC plugin works means it only analyzes Objective-C sections once. This catches alot of things but there are a number of cases where other libraries need to be loaded first due to information being referenced in another library. For instance errors like `Failed to determine base classname for category` can be caused by the class reference in the category being to a class outside of the loaded library. Once the library containing the class has been loaded, the section containing the category should be re-proccessed.
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From what I can tell the lock being taken in `SharedCache::~SharedCache` was purely for the decrement of `sharedCacheReferences`, however its an atomic so a lock isn't necessary. The lock being taken is extremely contentious and therefore often slow to be acquired. This resulted in a surprising amount of execution time spent in the `SharedCache` destructor. Nothing hugely significant but a quick and easy win to remove this single line of code.
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symbol list
We should think through a better way of handling upgrades, as v3 can load v2 dbs just fine, but there is no clean way to upgrade the info currently. We need SharedCache ser/des functions in DSCView.cpp
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`SharedCache::m_symbolInfos` isn't being serialized but there is an attempt to deserialize it. This commit adds in the code to serialize it.
I slightly modified the format because I didn't really understand how it was expected to be serialized based on the deserialization code. The deserialization code looked wrong to me but its likely a misunderstanding on my part. I kept it similar to how `m_exportInfos` is serialized.
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There seem to be a number of issues with slide info parsing. I decided the simplest fix was to largely mimick what `dyld` is doing.
Part of this process was to remove creating a vector of page starts and processing them in another loop below the one where they were read out. It wasn't clear to me the original design decision to separate it into 2 loops like that. I think this was part of the problem that was causing issues.
By adding rewrites in the same loop where page starts are being read out, it was much easier to mimick the code in `dyld` which I assume has to be correct. So as long as my copying was correct then I believe this should work as intended.
Not everything has been thoroughly tested but I'm pretty confident v3 and v5 are now working as intended. v2 should be but less testing of it has been done.
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The issue this commit fixes was causing `SharedCache::ParseAndApplySlideInfoForFile` to completely fail to work with v5 slide info, which had a lot of knock on effects, i.e. lots of Objective-C analysis was failing due to invalid pointers which hadn't been fixed up.
`dyld_cache_slide_info5` has 4 bytes of padding before `value_add`. Whilst `value_add` is not actually being read from, `SharedCache::ParseAndApplySlideInfoForFile` will read at a location in the file based on the size of the structure `dyld_cache_slide_info5`. This being off by 4 bytes basically broke v5 slide info fixups.
With this fix many more Objective-C functions have names and a lot more `msgSend` calls are fixed up.
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Copying the state from the cache into a new `SharedCache` object is done
with a global lock held and is so expensive that it results in much of
the shared cache analysis running on a single thread, with others
blocked waiting to acquire the lock.
The cache now holds a `std::shared_ptr` to the state. New `SharedCache`
objects take a reference to the cached state and only create their own
copy of it the first time they perform an operation that would mutate
it. The cached copy is never mutated, only replaced, so there is no
danger of modifying the state out from under a `SharedCache` object.
Since the copy happens at first mutation, it is performed without any
global locks held. This avoids blocking other threads.
This cuts the initial load time of a macOS shared cache from 3 minutes
to 70 seconds, and cuts the time taken to load and analyze AppKit from
multiple hours to around 14 minutes.
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The flags field was being left uninitialized which could result in the
region being mishandled during later analysis.
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There are typically only a few dozen mappings, while there can be
millions of pages. This reduces the amount of time spent populating the
mapping from region to file accessor along with the memory usage of the
same.
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api/MetadataSerializable.hpp is removed in favor of including
core/MetadataSerializable.hpp. Both headers defined types with the same
name leading to One Definition Rule violations and surprising behavior.
The serialization and deserialization context are now created on-demand
during serialization rather than being a member of
`MetadataSerializable`. This reduces the size of every serializable
object by ~220 bytes.
The context is passed explicitly as an argument to `Serialize` /
`Deserialize`. As a result, `Serialize` / `Deserialize` can now be free
functions rather than member functions.
Since `MetadataSerializable` is not used for dynamic dispatch,
the virtual methods are removed and the class is updated to be a class
template using CRTP. This allows delegating to the derived class's
`Load` and `Store` methods without the additional size overhead of the
vtable pointer in every serializable object.
These changes reduce the memory footprint of Binary Ninja after loading
the macOS shared cache and loading a single dylib from it from 8.3GB to
4.6GB.
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This is both a correctness fix and avoids leaking a massive amount of memory.
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`MMappedFileAccessor::ReadBuffer` was returning a heap-allocated
`DataBuffer`, but no callers were ever deleting it. There does not
appear to be any reason to heap allocate the `DataBuffer` as the type is
effectively a smart pointer wrapper around `BNDataBuffer`. Switch to
returning it by value instead.
Additionally, `MMappedFileAccessor::ReadBuffer` was allocating a buffer,
copying data into it, and then handing that allocation to the `DataBuffer`
constructor. The constructor copies data into a new allocation it
owns so this allocation is unnecessary and was being leaked.
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robust system for out-of-date databases
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This is an early release of our DSC processing plugin. We're still hard at work improving this feature. You should be able to just drop in a dyld_shared_cache and use the 'Shared Cache Triage' view to load and analyze images.
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