Some SWIs use some bits 31-27 for flags. With the introduction of dynamic areas into the memory map on RISC OS 3.50, and the OS ROM itself moving up high in RISC OS 5.00, it is now possible for memory to be located at addresses with these bits set. Thus some SWIs are limited in the range of memory to which pointers can be passed, and will fail mysteriously (possibly overwriting other areas of memory) if a pointer to memory with these bits sets is unwittingly passed.
This list may be incomplete:
SWI Register Flag bits
FileCore_DiscOp R1 0-7 (word aligned address is encoded in 26 bits)
and similarly for ADFS_DiscOp, RAMFS_DiscOp etc... Use FileCore_DiscOp64 instead.
FileCore_SectorDiscOp R1 0-7 (word aligned address is encoded in 26 bits)
and similarly for ADFS_SectorDiscOp, SCSI_SectorDiscOp etc... Use FileCore_DiscOp64 instead.
OS_HeapSort R1 29,30,31. Use OS_HeapSort32 instead.
OS_ReadLine R0 30,31. Use OS_ReadLine32 instead.
OS_SubstituteArgs R0 31. Use OS_SubstituteArgs32 instead.
Wimp_SendMessage R1 see SWI documentation.
Draw_ProcessPath R7 31 - use Draw v1.17 and R1 bit 26 instead.
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