sys/newlib: Bugfix, add missing syscalls (only stubs)

[jcarrano]

Add small stubs for _times and _link_r so that code using times() or link()/rename() can still compile. The functions are marked as not implemented and return invalid codes.

Issues/PRs references

Fixes #9051 .

[kaspar030]

does errno have to be cleared? Spec says, errno indicates error on error...

[jcarrano]

@kaspar030 You are right, this is an example from libgloss (part of newlib):

/* _times -- no clock, so return an error.  */
clock_t _times (struct tms *buf)
{
  errno = EINVAL;
  return (-1);
}

I'm fixing it.

[kaspar030]

please squash

[basilfx]

@jcarrano The build failed, because of unused parameters.

syscalls.c: In function '_times':
syscalls.c:546:28: error: unused parameter 'ptms' [-Werror=unused-parameter]
 clock_t _times(struct tms *ptms)

You can mark them as unused by adding (void) ptms; to _times.

[kaspar030]

Shouldn't this also use the errno variable from struct reent?

[jcarrano]

I copied it from libgloss, which is part of newlib.

[jcarrano]

@kaspar030 I changed over to _times_r(). What's curious is that in the newlib source, _times_r() is implemented in terms of times() and all the platform-specific syscall implementations in libgloss implement times(). However, after reading https://www.embecosm.com/appnotes/ean9/html/ch05s04.html I learned that the two options are possible depending on how the library is configured.

[jia200x]

@jcarrano any news on this?

[jcarrano]

@jia200x I addressed @kaspar030 review and squashed. Btw, I'm also working intermittently on what I think is a better fix (#9258 ), but this one should work for now.

[tcschmidt]

@kaspar030 do changes satisfy your concerns?

Already addressed

[danpetry]

OK I'm satisfied with the approach here, on the basis that it replicates the approach elsewhere and that that approach is being addressed more comprehensively in #9258. Implementation is also consistent with other functions in the module. Also, the added functions aren't actually used elsewhere meaning, for example, they won't have a memory impact anywhere except in the Lua interpreter. Would be good to address the above PR ASAP to avoid errors if other people try to use the related newlib functions.