Messages in this thread |  | | Date | Tue, 14 Apr 2015 15:56:44 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH v4 00/24] ILP32 for ARM64 |
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On Tue, Apr 14, 2015 at 11:51:54AM +0000, Pinski, Andrew wrote: > > On Apr 14, 2015, at 4:15 AM, Arnd Bergmann <arnd@arndb.de> wrote: > > On Tuesday 14 April 2015 10:45:43 Pinski, Andrew wrote: > >>> On Apr 14, 2015, at 3:08 AM, Arnd Bergmann <arnd@arndb.de> wrote: > >>> There are multiple ways of doing this: > >>> > >>> a) separate syscall table for arm64: as you say, this is the current approach, > >>> and I'd like to avoid that too > >>> b) add syscalls for ilp32 as additional numbers in the normal lp64 version of > >>> asm-generic/unistd.h, and share the binary tables between ilp32 and lp64 > >>> on aarch64 > >>> c) change asm-generic/unistd.h to generate three possible tables: instead of > >>> just native (lp64 or ilp32 depending on the arch), compat (support for > >>> existing ilp32 binaries on some architectures, there would also be a > >>> "modern" ilp32 variant that is a mix of the two, as your table today > >>> d) don't use the asm-generic/unistd.h table for aarch64-ilp32 at all, but instead > >>> reuse the table from arch/arm64/include/asm/unistd32.h > >>> > >>> I think you are referring to approach b) or c) above, but my preferred one > >>> would actually be d). > >> > >> D is the worst of all 4 options in my mind. The reason is when a new syscall is > >> added, then you have to update that file too. > > > > I don't know what the miscommunication is here, but the advantage of d is > > specifically that it is /less/ work to maintain: With the current approach, > > each new syscall that gets added needs to be checked to see if the normal > > aarch64 version works or if it needs another wrapper, while with d) we > > get the update for free, because we follow exactly what aarch32 is doing. > > More than that d won't work due to ucontext being different between > aarch32 and aarch64.
This too, I forgot to mention it (unless we restrict ILP32 to only 15 registers, reduced FP bank; in summary, it won't work).
> Also this abi is about to be used in a product so any changes need to > happen fast and need to thought out why making changes to it make > senses.
This is not our problem really. It's been pretty quiet on the ILP32 front for the past 6 months or more and just because a product is going to use it is not an argument to accept a long term ABI.
> Changing to use the aarch32 syscall #'s make less sense since this is > not a legacy syscalls.
That I agree. I'm fine with 32-bit only data structures but I really want to stick to the asm-generic/unistd.h syscalls for new ABIs.
-- Catalin
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