21.2. Mainframe registers
If you develop your own applications, it may be of use to know something about the mainframe register sets. A full description is in S/390 ELF Application Binary Interface Supplement and zSeries ELF Application Binary Interface Supplement, both available at http://www.linuxbase.org/spec/ELF/zSeries/.
21.2.1. zSeries registers
S/390 has 16 general-purpose registers of 32-bit width; with zSeries, the registers are 64-bit wide. The number of floating-point registers depends on the model. Older systems have only four floating-point registers; recent systems come with 16. The 16 registers were introduced together with the IEEE floating-point implementation. All Linux programs are able to use 16 floating-point registers. The ...
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