Re: [Xenomai] [Xenomai-git] Jan Kiszka : cobalt/kernel: Remove unused mode parameter from COBALT_SYSCALL

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On Thu, Jul 02, 2015 at 08:49:04PM +0200, Jan Kiszka wrote:
> On 2015-07-02 20:42, Gilles Chanteperdrix wrote:
> > On Thu, Jul 02, 2015 at 07:57:26PM +0200, Jan Kiszka wrote:
> >> On 2015-07-02 19:55, Gilles Chanteperdrix wrote:
> >>> On Thu, Jul 02, 2015 at 07:35:08PM +0200, Gilles Chanteperdrix wrote:
> >>>> On Thu, Jul 02, 2015 at 07:31:38PM +0200, Jan Kiszka wrote:
> >>>>> On 2015-07-02 18:56, Gilles Chanteperdrix wrote:
> >>>>>> On Thu, Jul 02, 2015 at 06:49:33PM +0200, Gilles Chanteperdrix wrote:
> >>>>>>> On Thu, Jul 02, 2015 at 06:44:06PM +0200, Jan Kiszka wrote:
> >>>>>>>> On 2015-07-02 18:30, Philippe Gerum wrote:
> >>>>>>>>> On 07/02/2015 05:39 PM, Jan Kiszka wrote:
> >>>>>>>>>> On 2015-07-02 17:24, Philippe Gerum wrote:
> >>>>>>>>>>> On 07/02/2015 05:20 PM, git repository hosting wrote:
> >>>>>>>>>>>> Module: xenomai-jki
> >>>>>>>>>>>> Branch: for-forge
> >>>>>>>>>>>> Commit: 99736c29a21a5e5536f8db9e580fd11cdb0eb0f2
> >>>>>>>>>>>> URL:    http://git.xenomai.org/?p=xenomai-jki.git;a=commit;h=99736c29a21a5e5536f8db9e580fd11cdb0eb0f2
> >>>>>>>>>>>>
> >>>>>>>>>>>> Author: Jan Kiszka <jan.kiszka@siemens.com>
> >>>>>>>>>>>> Date:   Thu Jul  2 17:12:39 2015 +0200
> >>>>>>>>>>>>
> >>>>>>>>>>>> cobalt/kernel: Remove unused mode parameter from COBALT_SYSCALL
> >>>>>>>>>>>
> >>>>>>>>>>> We want to keep this. At some point, maybe, we will be able to use this
> >>>>>>>>>>> information to instrument the code with calling context guards, or as
> >>>>>>>>>>> the source of the mode data in the syscall table. Today, it's at least
> >>>>>>>>>>> useful inline documentation, without having to browse the table.
> >>>>>>>>>>
> >>>>>>>>>> This only makes sense when cobalt_sysmodes can be generated from it.
> >>>>>>>>>> Currently it isn't, and I bet there are already plenty of
> >>>>>>>>>> inconsistencies, minimizing the value captured via COBALT_SYSCALL
> >>>>>>>>>> massively. So we should either get rid of cobalt_sysmodes or of that
> >>>>>>>>>> parameter.
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> "currently" is the point. If you feel implementing either aspects, i.e.
> >>>>>>>>> automatic tagging of the current context when traversing a cobalt call
> >>>>>>>>> based on the mode in the syscall macro, or generating the table data
> >>>>>>>>> based on the info, please do. If you feel fixing any consistency between
> >>>>>>>>> the two mode specs proving your bet right, please do as well. But for
> >>>>>>>>> now, I won't pick that commit.
> >>>>>>>>
> >>>>>>>> The approach of using COBALT_SYSCALL to define the mode only works if
> >>>>>>>> that is also the only place to define it. Let's see first if/how that
> >>>>>>>> can be achieved.
> >>>>>>>
> >>>>>>> That can be achieved by getting the macro to adding data in a
> >>>>>>> special section, then use that section as the syscall table with
> >>>>>>
> >>>>>> Use that section to build the syscall table. Or sort it. The section
> >>>>>> can not be used directoy, the syscalls are not in the right order.
> >>>>>
> >>>>> What would be the key for sorting? Semantically the syscall number, but
> >>>>> how to translate that into a key (i.e. a symbol name) that the linker
> >>>>> could sort properly?
> >>>>>
> >>>>> As far as I can see for x86, the kernel uses a host script to generate
> >>>>> the syscall table which is defined arch/x86/syscalls/syscall_*.tbl -
> >>>>> presorted. That step also generates the #defines for the syscall numbers.
> >>>>
> >>>> Yes, we probably need to add the syscall number to the
> >>>> COBALT_SYSCALL macro. Or build it from the function name. A second
> >>>> possibility is to keep the current table, but do not fill the flag
> >>>> field, and use the information in the section to find back each
> >>>> syscall and fill the blanks.
> >>>
> >>> Yet another possibility is to run a script on the sources, which
> >>> generates the table as .c code. The script would simply handle the
> >>> calls to the COBALT_SYSCALL macro. This can be done with sed or awk
> >>> even. And this does not require playing with the linker script.
> >>
> >> I more and more believe that is actually only feasible approach. The
> >> linker tricks seem to fail because we cannot prepare the required input
> >> as needed. If they worked, the kernel would surely use one of them.
> > 
> > Actually the awk script is astonishingly simple.
> > 
> > find kernel/cobalt -name '*.c' | xargs cat | awk -f foo.awk
> > 
> > With foo.awk
> > 
> > match($0, /COBALT_SYSCALL\([^,]*, [^,]*/)  {
> > 	str=substr($0, RSTART + 15, RLENGTH - 15)
> > 	match(str, /[^,]*/)
> > 	syscall=substr(str, RSTART, RLENGTH)
> > 	seen[syscall]=1;
> > 	print "__COBALT_MODE(" str "),"
> > }
> > 
> > match($0, /__COBALT_CALL_ENTRY\([^)]*/)  {
> > 	syscall=substr($0, RSTART + 20, RLENGTH - 20)
> > 	intable[syscall]=1
> > }
> > 
> > END {
> > 	for (s in intable)  {
> > 		if (s != "" && s != "__name" && !seen[s])
> > 			print "missed syscall \"" s "\" implementation!"
> > 	}
> > }
> 
> Ah, good that you have the right awk foo. I'll give this a try.

Ok, the script issues a list of __COBALT_MODE statements which
replaces the contents of the cobalt_sysmodes table. You probably want
to exit 1 when we missed a COBALT_SYSCALL declaration. We could just
as easily generate the contents of the cobalt_syscalls table, but in
that case, if the script misses a COBALT_SYSCALL declaration, we
have no way of knowing.

> 
> > 
> > The problem will be to re-run the script when a new syscall is added
> > or a file is modified.
> 
> That should be simple. Working on the Makefile bits...

Actually, the only way I see is to regenerate the table at every
compilation.

-- 
					    Gilles.
https://click-hack.org