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The Assembler language on z/OS Application programming on z/OS |
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Assembler language is a symbolic programming language that can be used to code instructions instead of coding in machine language. The Assembler language is the symbolic programming language that is closest
to the machine language in form and content, and therefore is an excellent
candidate for writing programs in which:
Assembler language is made up of statements that represent either instructions or comments. The instruction statements are the working part of the language, and they are divided into the following three groups:
The assembler produces a program listing containing information that was generated during the various phases of the assembly process.2 It is really a compiler for Assembler language programs. The assembler also produces information for other processors, such as a binder (or linker, for earlier releases of the operating system). Before the computer can execute your program, the object code (called an object deck or simply OBJ) has to be run through another process to resolve the addresses where instructions and data will be located. This process is called linkage-editing (or link-editing, for short) and is performed by the binder. The binder or linkage editor uses information in the object decks to combine them into load modules. At program fetch time, the load module produced by the binder is loaded into virtual storage. After the program is loaded, it can be run. Figure 1 shows these steps. Related reading: You can find more information about using Assembler language on z/OS in the IBM publications, HLASM General Information, GC26-4943, and HLASM Language Reference, SC26-4940. 1 Subroutines are programs that are invoked
frequently by other programs and by definition should be written with performance
in mind. Assembler language is a good choice for a subroutine. 2 A program
listing does not contain all of the information that is generated during the
assembly process. To capture all of the information that could possibly be
in the listing (and more), the z/OS® programmer can specify an assembler
option called ADATA to have the assembler produce a SYSADATA file as output.
The SYSADATA file is not human-readable—its contents are in a form that is
designed for a tool to process. The use of a SYSADATA file is simpler for
tools to process than the older custom of extracting similar data through "listing
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Copyright IBM Corporation 1990, 2010
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