#Purebasic image memory allocation code
#Purebasic image memory allocation free

Accessing the heap is as simple as storing values in a specified address. Anything besides the zero page is platform-specific. The 'heap' can be considered the zero page, or any other section of RAM that the hardware allows for general access. It's all there for the programmer to use. Since this is assembly, there is no structured system for allocating/deallocating memory. The next 256 bytes are reserved for the stack. The first 256 bytes in the 6502's address space are collectively referred to as the 'zero page' and can be used for any purpose. WALEN EQU *-DYNAREA length of obtained areaĮND STOREXNO end of module 6502 Assembly LTORG, have assembler build literal pool STORAGE RELEASE,ADDR=(10),LENGTH=(9),EXECUTABLE=NOĬONSTANTS DS 0D constant section, aligned for LARL * in obtained storage location, and branch to it * copy instruction sequence SR Reg15,Reg15 Branch Reg14 to DATA1 USING DYNAREA,10 using for dynamic memory area STORAGE OBTAIN,LENGTH=(9),EXECUTABLE=NO,LOC=ANY LA 9,WALEN load memory length in Register 9 LARL 12,CONSTANTS load address relative long IEABRCX DEFINE convert based to relative branchesīAKR 14,0 callers registers to linkage stack

#Purebasic image memory allocation code

SYSSTATE AMODE64=NO,ARCHLVL=3 gen z9+, z/OS 2.1+ bin code Though not a requirement for this type of sample code it is a best practice in assembler coding.

Finally, the code is REENTRANT, meaning it could be loaded in a system module directory (LINKLIST, LPA), and executed simultaneously by multiple callers.

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.

The code copies two instructions to the obtained storage and branches to it. If on a z14 or newer machine and EXECUTABLE=NO then the module will ABEND S0C4-4. The code below will execute successfully if EXECUTABLE=YES (or defaulted to), or if running on a pre z14 machine.

One of the many functions of STORAGE over GETMAIN/FREEMAIN is illustrated: EXECUTABLE=NO.

The STORAGE macro is used (PC call to the storage routine) instead of GETMAIN/FREEMAIN (SVC based.

The IEABRCX system macro will conveniently convert all based branch instructions to their relative equivalents. All modern day z/OS compilers generate baseless code, and so should the 'raw assembler programmer'.

This is referred to as Relative addressing.

The code is 'baseless', meaning no base register has been established for the entry point of the module.

PLIST EQU * 10-Byte GETMAIN/FREEMAIN Parameter ListĭC A(256) Number of Bytes Max=16777208 ((2**24)-8)ĭC X'0000' (Unconditional Request Subpool 0)Įxample below shows de facto modern day use of HLASM techniques: * DS A Address of Stg Area (Aquired or to be Freed)

#Purebasic image memory allocation free

* Request to Free Storage Managed by 'FREEMAIN' Supervisor Call (SVC 5) GOTSTG L Load Reg (any Reg) with Addr of Aquired Stg LA 1,PLIST Point Reg 1 to GETMAIN/FREEMAIN Parm List * Request to Get Storage Managed by 'GETMAIN' Supervisor Call (SVC 4)