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Additional comment in ObjectFileMachO::ParseSymtab to explain 

the layout of the dyld shared cache file and how we're stepping
through it; also use offsetof to find offsets of struct elements.

llvm-svn: 158962
This commit is contained in:
Jason Molenda 2012-06-22 03:28:35 +00:00
parent 321d41a871
commit f813086c85
1 changed files with 14 additions and 6 deletions
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20
lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
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@ -1494,7 +1494,6 @@ struct lldb_copy_dyld_cache_header
uint64_t localSymbolsOffset;
uint64_t localSymbolsSize;
};
struct lldb_copy_dyld_cache_local_symbols_info
{
uint32_t nlistOffset;
@ -1504,7 +1503,6 @@ struct lldb_copy_dyld_cache_local_symbols_info
uint32_t entriesOffset;
uint32_t entriesCount;
};
struct lldb_copy_dyld_cache_local_symbols_entry
{
uint32_t dylibOffset;
@ -1512,6 +1510,18 @@ struct lldb_copy_dyld_cache_local_symbols_entry
uint32_t nlistCount;
};
/* The dyld_cache_header has a pointer to the dyld_cache_local_symbols_info structure (localSymbolsOffset).
The dyld_cache_local_symbols_info structure gives us three things:
1. The start and count of the nlist records in the dyld_shared_cache file
2. The start and size of the strings for these nlist records
3. The start and count of dyld_cache_local_symbols_entry entries
There is one dyld_cache_local_symbols_entry per dylib/framework in the dyld shared cache.
The "dylibOffset" field is the Mach-O header of this dylib/framework in the dyld shared cache.
The dyld_cache_local_symbols_entry also lists the start of this dylib/framework's nlist records
and the count of how many nlist records there are for this dylib/framework.
*/
// Process the dsc header to find the unmapped symbols
//
// Save some VM space, do not map the entire cache in one shot.
@ -1520,9 +1530,7 @@ struct lldb_copy_dyld_cache_local_symbols_entry
{
DataExtractor dsc_header_data(dsc_data_sp, m_data.GetByteOrder(), m_data.GetAddressByteSize());
struct lldb_copy_dyld_cache_header* dsc_header_dummy = NULL;
uint32_t offset = sizeof(dsc_header_dummy->magic);
uint32_t offset = offsetof (struct lldb_copy_dyld_cache_header, mappingOffset);
uint32_t mappingOffset = dsc_header_data.GetU32(&offset);
// If the mappingOffset points to a location inside the header, we've
@ -1530,7 +1538,7 @@ struct lldb_copy_dyld_cache_local_symbols_entry
if (mappingOffset >= sizeof(struct lldb_copy_dyld_cache_header))
{
offset = (uint32_t)(uintptr_t)&dsc_header_dummy->localSymbolsOffset;
offset = offsetof (struct lldb_copy_dyld_cache_header, localSymbolsOffset);
uint64_t localSymbolsOffset = dsc_header_data.GetU64(&offset);
uint64_t localSymbolsSize = dsc_header_data.GetU64(&offset);