Inside Macintosh: Mac OS Runtime Architectures /

Chapter 8 - PEF Structure

The Container Header

The container header contains information about the specific PEF container. The container header data structure is of fixed size (40 bytes) and has the form shown in Listing 8-1.

Listing 8-1 PEF container header data structure

struct PEFContainerHeader {
   OSTypetag1;           
   OSTypetag2;           
   OSTypearchitecture;   
   UInt32formatVersion;  
   UInt32dateTimeStamp;  
   UInt32oldDefVersion;  
   UInt32oldImpVersion;  
   UInt32currentVersion; 
   UInt16sectionCount;   
   UInt16instSectionCount; 
   UInt32reservedA;   
};

The fields in the container header are as follows:

• The tag1 field (4 bytes) designates that the container uses an Apple-defined format. This field must be set to Joy! in ASCII.
• The tag2 field (4 bytes) identifies the type of container (currently set to peff in ASCII).
• The architecture field (4 bytes) indicates the architecture type that the container was generated for. This field holds the ASCII value pwpc for the PowerPC CFM implementation or m68k for CFM-68K.
• The formatVersion field (4 bytes) indicates the version of PEF used in the container. The current version is 1.
• The dateTimeStamp field (4 bytes) indicates when the PEF container was created. The stamp follows the Macintosh time-measurement scheme (that is, the number of seconds measured from January 1, 1904).
• The next three fields, oldDefVersion, oldImpVersion, and currentVersion (4 bytes each), contain version information that the Code Fragment Manager uses to check shared library compatibility. For more information about version checking, see "Checking for Compatible Import Libraries" (page 1-15).
• The sectionCount field (2 bytes) indicates the total number of sections contained in the container.
• The instSectionCount field (2 bytes) indicates the number of instantiated sections. Instantiated sections contain code or data that are required for execution.
• The reservedA field (4 bytes) is currently reserved and must be set to 0.

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© Apple Computer, Inc.
11 MARCH 1997