Re: microblaze syscall list

[Michal Simek <monstr@seznam.cz>]

Hi Arnd,

>> I would like to fix syscalls in Microblaze repo. Can you give me a hint how to
>> do it?
> 
> I think we need to do it on a case-by-case basis, best here on the
> linux-arch mailing list. I'm sure there are some controversial ones,
> but most should be pretty clear.
>  
>> I look at Blackfin arch and I compared files with microblaze. There are some
>> differences but not so much.
>> Can you tell me how to test it which syscall is necessary for platform.
>> I have never found any documentation about.
> 
> Hopefully we can get to this kind of documentation by the end of this
> discussion. scripts/checksyscalls.sh is some part of the documentation,
> and we can refine that.
:-)

> Maybe we can even have an asm-generic/unistd.h that defines all the
> still relevant syscalls, plus a per-architecture range that you can
> use for microblaze-specific calls in your own unistd.h.

That will be really useful. Good idea.

>> In my syscall_table.S (on some arch in entry.S) is one big jump table with
>> reference to syscalls. In unistd.h is definition.
>>
>> Is there any convention which syscalls are use for all archs and which are
>> architecture specific?
> 
> Not really. There are very few syscalls that are needed only on certain
> architectures. The more common case is that a syscall has been replaced
> by a more complex interface, and a new architecture only needs one of the
> two, while older architectures still need both.
> 
> Let me just comment on your syscall table as it is today:
> 
>> ENTRY(sys_call_table)
>> 	.long sys_restart_syscall	/* 0 - old "setup()" system call,
>> 					 * used for restarting */
> 
> The comment is irrelevant and misleading -- microblaze never had sys_setup.

I removed this comment.

>> 	.long sys_exit
>> 	.long sys_ni_syscall		/* was fork */
> 
> it might be useful to renumber your calls once all the irrelevant ones
> have been removed, so you can get rid of all the sys_ni_syscalls here.

I'll delete all sys_ni_syscall from syscall_table.S and I'll remove it from
unistd.h too. I hope I'll keep the same call numbers.

>> 	.long sys_read
>> 	.long sys_write
>> 	.long sys_open			/* 5 */
> 
> Since we have all the new sys_*at calls like openat, we don't really
> need the old versions any more. The kernel implementation of sys_open
> basically calls openat. You could do the same in libc instead.
> Don't know if that's worth it though, opinions?

I looked at it and there are the different arguments for open and openat
syscalls. Implementation is almost the same. I keep it now.

>> 	.long sys_close
>> 	.long sys_waitpid
> 
> waitpid and wait4 can be replaced with waitid

Can I keep number of syscall(unistd.h) and only add reference to waitid in
syscall_table? or just remove?

>> 	.long sys_creat
>> 	.long sys_link
>> 	.long sys_unlink		/* 10 */
>> 	.long sys_execve_wrapper
> 
> having an execve_wrapper instead of execve looks like a strange convention,
> though I guess you had a good reason for it, could you explain?
>
> This one looks architecture specific, so you may want to rename it
> microblaze_execve_wrapper instead of sys_execve_wrapper.

I looked at it and the same of style is used in arm
(arch/arm/kernel/entry-common.S) and some others arch. This wrapper only set one
parameter to correct pointer to stack.

I'll comment the rest later. I need time to look at it.

Thanks for your big help. I really appreciate this.

Michal