[DSC] Rework handling of .symbols files to be compatible with iOS 15

In some iOS 15 caches, the .symbols file's mapping has an address of 0.
This would cause it to be returned by `SharedCache::GetEntryContaining`
and loaded into the view.

The .symbols file contains the local symbol tables for images in the
shared cache. It is not intended to be mapped into the same address
space as the rest of the shared cache.

`SharedCache` now tracks the symbols cache entry separately from other
entries. A dedicated `VirtualMemory` region is used when accessing the
data it contains. This could be a `FileAccessor`, but that would require
additional changes within `SharedCacheMachOHeader`.

`SharedCacheMachOProcessor` now directly accesses the local symbols
cache entry rather than needing to search for it.

1 files changed, 13 insertions, 4 deletions

diff --git a/view/sharedcache/core/SharedCache.cpp b/view/sharedcache/core/SharedCache.cpp
index 0a14cfaf..c084c692 100644
--- a/view/sharedcache/core/SharedCache.cpp
+++ b/view/sharedcache/core/SharedCache.cpp
@@ -91,10 +91,8 @@ CacheEntry CacheEntry::FromFile(const std::string& filePath, const std::string&
 	{
 		// We found a single symbols cache entry file. Mark it as such!
 		type = CacheEntryType::Symbols;
-		// Adjust the mapping for the symbol file, they seem to be only for the header.
-		// If we do not adjust the mapping than we will not be able to read the symbol table through the virtual memory.
-		mappings[0].fileOffset = 0;
-		mappings[0].size = file->Length();
+		// Symbol files are not mapped into the address space.
+		mappings.clear();
 	}
 	else if (mappings.size() == 1 && header.imagesCountOld == 0 && header.imagesCount == 0
 		&& header.imagesTextOffset == 0)
@@ -231,6 +229,17 @@ void SharedCache::AddEntry(CacheEntry entry)
 	// Get the file accessor to associate with the virtual memory region.
 	auto fileAccessor = FileAccessorCache::Global().Open(entry.GetFilePath());
 
+	if (entry.GetType() == CacheEntryType::Symbols)
+	{
+		m_localSymbolsEntry = std::move(entry);
+		// Map the entire file into its own virtual memory space.
+		// This is necessary due to code that processes symbols being written in terms of a `VirtualMemory`
+		// rather than something more generic.
+		m_localSymbolsVM = std::make_shared<VirtualMemory>(m_vm->GetAddressSize());
+		m_localSymbolsVM->MapRegion(fileAccessor, {0, fileAccessor.lock()->Length()}, 0);
+		return;
+	}
+
 	// Populate virtual memory using the entry mappings, by doing so we can now
 	// read the memory of the mapped regions of the cache entry file.
 	const auto& mappings = entry.GetMappings();