HLASM: V1R6 Language Ref

Beginning of a source moduleAt linking timeAs specified by linker or binder control statements, the linker or bindercombines the object code of one or more sections into one load module orprogram object. It also calculates the addresses needed to accommodatecommon sections and external dummy sections from different objectmodules. In addition, it calculates the space needed to accommodateexternal dummy sections.You can specify the relocatable address of the starting point for programexecution in a linker control statement or request a starting address in theoperand field of an assembler END instruction.At program fetch timeThe control program loads the load module or program object into virtualstorage. All the relocatable addresses are converted to fixed locations instorage.At execution timeThe control program passes control to the loaded program now in virtualstorage, and your program is run.SectionsIn the load module model, control sections may generate machine language textcontaining instructions and data, or define mappings of storage areas to bereferenced at execution time. Control sections that generate machine language textare called executable control sections, even though they may contain only data.Control sections that create only mappings are called reference control sections.z/VM and z/OSIn the program object model, sections may define classes containing elements.(Classes are described in “Classes (z/OS and CMS)” on page 57.) Elements maycontain machine language text or define mappings, or both. Elements may in turncontain one or more parts, which are described at “Parts (z/OS and CMS)” on page59.Elements containing machine language text are usually linked in a classcomprising other elements containing machine language text, and elementsdefining mappings are usually linked in a class with other elements definingmappings.The section name is used in binder operations to refer to its entire collection ofelements and parts, but a program object section is not the same as a load modulecontrol section. A section name may be referenced as an external name only ifdefined as an entry point in an element belonging to that section. (By default, theassembler will generate an entry point in class B_TEXT with the section’s name. See“Classes (z/OS and CMS)” on page 57 for more information.)End of z/VM and z/OSThe term “executable” is used to describe both executable control sections in theload module model, or sections in the program object model.You initiate a section by using the START, CSECT, or RSECT instruction, asdescribed below:52 HLASM: V1R6 Language Ref