OS/2 Loader (with hardcoded physical memory limits)

os2ldrs with hardcoded physical memory limits Steven H. Levine 2022-12-12 If you are running ArcaOS, you should not be reading this. You should have already read https://www.arcanoae.com/wiki/how-to-get-a-trap-dump/ and you should have followed the direction in the wiki. These tools predate ArcaOS2 and are obsolete and unsupported by anyone if you are running ArcaOS. If you don't know why you are thinking about using one of these loaders, you probably should not even be thinking about using one of these loaders. These loaders exist to allow systems with more than 2GB of physical RAM to write a system dump file to 2GB FAT formatted partitions. These loaders are intended to be used when you are unable to capture a system dump to a 4GB DUMPFS partition. For not yet fully understood reasons, attempting to capture a system dump to a DUMPFS formatted volume on a system with 4GB of physical RAM often fails. If the DUMPFS method works for you, there is no really good reason to use one of these loaders. The downside of using one of these loaders is that eCS/OS2 will have less available physical memory. However, for a typical application mix, 2GB of physical RAM is more than will ever be needed. These loaders limit the detected physical memory to a hardcoded value. This limits the amount of physical memory that eCS will use and generally allows a usable system dump to be written to a 2GB FAT formatted volume. The distribution contains two patched loaders: 10-02-13 23:50 43,008 0 os2ldr_512MB 1-04-16 12:59 43,008 0 os2ldr_2GB os2ldr_2GB limits the detected physical memory to 2GB-1MB. os2ldr_512MB limits the detected memory to 512MB. The 512MB version has the benefit of producing a smaller system dump. However, if your application mix requires more than 512MB of physical RAM to perform well, use the 2GB version. == Known Limitations == The patched loaders only work with SMP kernels. The system must contain more physical memory than the patched loader will claim exists. For example, using the 2GB patched loader on a system with only 1GB of physical memory will produce undefined results. == Installation == The active os2ldr will be in the root of your boot volume. Decide which patched os2ldr best suits your needs. To install the patched os2ldr - If the installed os2ldr is hidden, make it visible. - Save a copy of the original, active os2ldr as os2ldr.saved. - Copy and rename the selected, patched os2ldr and overwrite the original active os2ldr. - Reboot. To uninstall the patched os2ldr - Replace the active os2ldr with os2ldr.saved. - Reboot. == Theory of Operation == The patched loaders are based on the SMP os2ldr distributed eCS 2.x. This os2ldr was originally the 14.106 SMP retail os2ldr distributed with FP6 GA. This eCS 2.x os2ldr has the standard patches installed and reports itself as 2-13-07 10:27 43,008 0 os2ldr with the md5 sum aba04bea4ac9e4d04910d7a82e6de333 *os2ldr Modern BIOS's support the Int 15 e820 BIOS function. This function returns entries from a table that describes the physical memory ranges known to the BIOS. The original os2ldr uses the list entry that corresponds to the physical memory starting at 1MB to set the physical memory size. The patched os2ldrs ignore the reported size of this memory block and uses the hardcoded size of 2GB or 512MB. The original code is cseg3:32D9 mov ebx, [di+8] ; get byte count from table entry cseg3:32DD shr ebx, 10 ; convert from bytes to KB The 2GB patch is cseg3:32D9 mov ebx, 1ff000h ; force to 2GB-1MB (in KB) cseg3:32DF nop cseg3:32E0 nop The 512MB patch is cseg3:32D9 mov ebx, 80000h ; force to 512MB (in KB) cseg3:32DF nop cseg3:32E0 nop == IBM patch files == ; Patch for 2GB-1MB ; 200000 - 1000 = 1FF000 FILE OS2LDR VER 32D9 66BB000020009090 CHA 32D9 66BB00001FF09090 ; Patch for 512KB FILE OS2LDR VER 32D9 668B5D0866C1EB0A CHA 32D9 66BB000008009090 == Changelog == - Limit memory detected by os2ldr_2GB from 2GB to 2GB-1MB. On some systems a 2GB dump file would not fit in the availabe file space on a 2GB FAT volume.