The benefit to learning s390x assembler over others is that there are actually still experts around that program entirely in the macro assembler, and environments that still expect or require it (technically, its a solved problem to link against the assembler code from Metal C, but all the docs and APIs are specified entirely in assembler for much of the low level OS internals, and you really do need to know it to work with it in any significant professional capacity).
Its tough to learn on x86 or ARM, because there has been a lot of standardization towards C, and that is sorta the expected low level API/ABI even at the kernel level in 2024. Calling conventions have been standardized, and really very little actual programming is done manually in assembly these days. So its sort of artificial trying to learn assembly on those ISAs these days. Certainly there are not many APIs specified in assembly. Perhaps one exception would be compiler/linker backends, but that is a whole other can of worms you've gotta learn if you go that route.
IBM Z is different in that respect. It makes it probably a more difficult and unwieldy platform overall if you just wanna make a quick app and ship (why I'm not advocating you all go out and buy mainframes lol), but for learning how to program assembler "in the real world", its the last bastion of a much older school of programming and a great learning environment that will challenge some of the assumptions you maybe have picked up that actually come from Unix or C and not the ISAs themselves.
Its also, in my humble opinion, a pretty nice macro assembler to actually work with. Its had a lot of development over the years (perhaps as a result of it remaining a significant force in the systems programming world for mainframes long after similar programming interfaces were quietly retired on newer platforms), and so I quite like the actual assembler itself, now known as IBM HLASM.
I tend to recommend newcomers pick up a free pdf book from here by the esteemed John Ehrman (RIP)
> Perhaps one exception would be compiler/linker backends
I think for compiler+linker backends it's really important to have a decent reading level of assembly. In llvm, most of the work will be in instruction selection and you'll then read the results. With lld you write a very stylized handler with some switch statements and very stylized macro incantations. And read the results with dis and elfdump.
Its tough to learn on x86 or ARM, because there has been a lot of standardization towards C, and that is sorta the expected low level API/ABI even at the kernel level in 2024. Calling conventions have been standardized, and really very little actual programming is done manually in assembly these days. So its sort of artificial trying to learn assembly on those ISAs these days. Certainly there are not many APIs specified in assembly. Perhaps one exception would be compiler/linker backends, but that is a whole other can of worms you've gotta learn if you go that route.
IBM Z is different in that respect. It makes it probably a more difficult and unwieldy platform overall if you just wanna make a quick app and ship (why I'm not advocating you all go out and buy mainframes lol), but for learning how to program assembler "in the real world", its the last bastion of a much older school of programming and a great learning environment that will challenge some of the assumptions you maybe have picked up that actually come from Unix or C and not the ISAs themselves.
Its also, in my humble opinion, a pretty nice macro assembler to actually work with. Its had a lot of development over the years (perhaps as a result of it remaining a significant force in the systems programming world for mainframes long after similar programming interfaces were quietly retired on newer platforms), and so I quite like the actual assembler itself, now known as IBM HLASM.
I tend to recommend newcomers pick up a free pdf book from here by the esteemed John Ehrman (RIP)
https://idcp.marist.edu/assembler-resources
along with the POPs specified above. And make an account on zXplore or similar and play around after doing the (very short) introductory portion.