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Memory allocation: Difference between revisions
→{{header|360 Assembly}}
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* The code is "baseless", meaning no base register has been established for the entry point of the module. This is referred to as Relative addressing. All modern day z/OS compilers generate baseless code, and so should the "raw assembler programmer". The IEABRCX system macro will conveniently convert all based branch instructions to their relative equivalents.
* The STORAGE macro is used (PC call to the storage routine) instead of GETMAIN/FREEMAIN (SVC based. Stabilised (no new functions).
* One of the many functions of STORAGE over GETMAIN/FREEMAIN is illustrated: EXECUTABLE=NO. The code below will execute successfully if EXECUTABLE=YES (or defaulted to), or if running on a pre z14 machine. If on a z14 or newer machine and EXECUTABLE=NO then the module will ABEND S0C4-4. The code copies two instructions to the obtained storage and branches to it.
* The code shows the use of the system supplied linkage stack to save caller's registers (BAKR) and restore them on return (PR), as opposed to STM/LM of the caller's register contents.
* Finally, the code is REENTRANT, meaning it could be loaded in a system module directory (LINKLIST, LPA), and executed simultaneously by multiple callers. Though not a requirement for this type of sample code it is a best practice in assembler coding.
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