Please Please put back Sys/io.h emulation for armhf and possibly aarch64

[Luís Palma Nunes Mendes]

Dear Florian Weimer, 

Thanks for the quick reply. I will have a look with the Linux kernel
maintainers to see what could be a possible alternate path to
re-introduce similar support. 

Cheers, 

Luís 

On 2021-06-16 12:34, Florian Weimer wrote:

> * Luís Palma Nunes Mendes via Libc-alpha:
> 
>> The commit that removed the support, according to Carlos O'Donell was
>> this one: The rationale is given in the commit:
>> 
>> commit 6b33f373c7b9199e00ba5fbafd94ac9bfb4337b1
>> Author: Florian Weimer
>> Date:   Wed May 29 16:53:09 2019 +0200
>> 
>> arm: Remove ioperm/iopl/inb/inw/inl/outb/outw/outl support
>> 
>> Linux only supports the required ISA sysctls on StrongARM devices,
>> which are armv4 and no longer tested during glibc development
>> and probably bit-rotted by this point.  (No reported test results,
>> and the last discussion of armv4 support was in the glibc 2.19
>> release notes.)
>> 
>> Except that I was using it with armv7 for PCIe, with the kernel
>> configuration:
>> 
>> -> General setup->Configure standard Kernel features (expert
>> users)->Sysctl syscall support->Enable
> 
> The string "Sysctl syscall support" was removed from the upstream kernel
> with this commit:
> 
> commit 61a47c1ad3a4dc6882f01ebdc88138ac62d0df03
> Author: Eric W. Biederman <ebiederm@xmission.com>
> Date:   Tue Oct 1 13:01:19 2019 -0500
> 
> sysctl: Remove the sysctl system call
> 
> This system call has been deprecated almost since it was introduced, and
> in a survey of the linux distributions I can no longer find any of them
> that enable CONFIG_SYSCTL_SYSCALL.  The only indication that I can find
> that anyone might care is that a few of the defconfigs in the kernel
> enable CONFIG_SYSCTL_SYSCALL.  However this appears in only 31 of 414
> defconfigs in the kernel, so I suspect this symbols presence is simply
> because it is harmless to include rather than because it is necessary.
> 
> As there appear to be no users of the sysctl system call, remove the
> code.  As this removes one of the few uses of the internal kernel mount
> of proc I hope this allows for even more simplifications of the proc
> filesystem.
> 
> Which I think went into Linux 5.5.
> 
> So we can't support it in glibc now even if we wanted to.
> 
> We are not going to bring back this emulation.  Of course, you can take
> the old implementation and copy it into your application if that's what
> you want.
> 
> Thanks,
> Florian