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Chapter 8 - PEF Structure / The Loader Section

The Loader Header

The loader header data structure is of fixed size (56 bytes) and has the form shown in Listing 8-3.

Listing 8-3 Loader header data structure

struct PEFLoaderInfoHeader {
   SInt32mainSection;          
   UInt32mainOffset;           
   SInt32initSection;          
   UInt32initOffset;           
   SInt32termSection;          
   UInt32termOffset;           
   UInt32importedLibraryCount; 
   UInt32totalImportedSymbolCount; 
   UInt32relocSectionCount;    
   UInt32relocInstrOffset;     
   UInt32loaderStringsOffset;  
   UInt32exportHashOffset;     
   UInt32exportHashTablePower; 
   UInt32exportedSymbolCount;  
};

The fields in the loader header are as follows:

• The mainSection field (4 bytes) specifies the number of the section in this container that contains the main symbol. If the fragment does not have a main symbol, this field is set to -1.
• The mainOffset field (4 bytes) indicates the offset (in bytes) from the beginning of the section to the main symbol.
• The initSection field (4 bytes) contains the number of the section containing the initialization function's transition vector. If no initialization function exists, this field is set to -1.
• The initOffset field (4 bytes) indicates the offset (in bytes) from the beginning of the section to the initialization function's transition vector.
• The termSection field (4 bytes) contains the number of the section containing the termination routine's transition vector. If no termination routine exists, this field is set to -1.
• The termOffset field (4 bytes) indicates the offset (in bytes) from the beginning of the section to the termination routine's transition vector.
• The importedLibraryCount field (4 bytes) indicates the number of imported libraries.
• The totalImportedSymbolCount field (4 bytes) indicates the total number of imported symbols.
• The relocSectionCount field (4 bytes) indicates the number of sections containing load-time relocations.
• The relocInstrOffset field (4 bytes) indicates the offset (in bytes) from the beginning of the loader section to the start of the relocations area.
• The loaderStringsOffset field (4 bytes) indicates the offset (in bytes) from the beginning of the loader section to the start of the loader string table.
• The exportHashOffset field (4 bytes) indicates the offset (in bytes) from the beginning of the loader section to the start of the export hash table. The hash table should be 4-byte aligned with padding added if necessary.
• The exportHashTablePower field (4 bytes) indicates the number of hash index values (that is, the number of entries in the hash table). The number of entries is specified as a power of two. For example, a value of 0 indicates one entry, while a value of 2 indicates four entries.

  If no exports exist, the hash table still contains one entry, and the value of this field is 0.

• The exportedSymbolCount field (4 bytes) indicates the number of symbols exported from this container.