Re: [PATCH v2] newlib: libm: workaround ar duplicate member behavior

[Corinna Vinschen <vinschen@redhat.com>]

On Feb 22 12:17, Mike Frysinger wrote:
> On 22 Feb 2022 12:34, Jon Turney wrote:
> > On 22/02/2022 11:31, Corinna Vinschen wrote:
> > > On Feb 21 19:21, Mike Frysinger wrote:
> > >> GNU ar has undocumented behavior where it doesn't dedupe its inputs if
> > >> they're all on the same command line, so we have to dedupe ourselves.
> > >> ---
> > >> v2
> > >> - use awk to dedupe the object list
> > 
> > I think this could still at least use a comment about how the ordering 
> > of the inputs relates to which duplicate object are dropped and which 
> > are kept.
> 
> i had updated the comment locally already and just hadn't posted it:
> ## GNU ar has undocumented behavior when specifying the same name multiple times
> ## in a single invocation, so we have to dedupe ourselves.  The algorithm here:
> ## - Generates the set of unique objects based on the basename.
> ## - Favors objects later in the list (since machine objects come last).
> ## - Outputs object list in same order as input for reproducibility.
> 
> > (I'm assuming cpu-specific ones are meant to be kept in preference to 
> > generic routines, but how does this achieve that?)
> > 
> > > This seems to work.
> > > 
> > > However, what do we have to do in future to make sure the order is
> > > always correct?
> 
> i've documented this in 3 places, so think it's fine.
> 
> (1) libc/Makefile.inc & (2) libm/Makefile.inc both have:
> ## The order of includes is important for two reasons:
> ## * The integrated documentation (chapter ordering).
> ## * Object overridding -- machine dir must come last.
> ## Do not change the order without considering the doc impact.
> 
> (3) in the heavily rewritten build documentation i sent out [1].
> it's pending review from folks, so hasn't been merged yet.
> 
> > > And the heritic question: Wouldn't it be safer to keep the old
> > > per-subdir lib.a logic?
> 
> i think this is a false dichotomy.  the lib.a logic has the same problem,
> albeit it was never documented: if the order of SUBDIRS isn't maintained,
> then the machine overrides do not work correctly.  if the order of the
> lib.a unpacking was not done correctly, then the machine overrides do not
> work correctly.  the fact that it's been "stable for so long" isn't due
> to the code being written well (no offense), it's because it's been so
> dense & undocumented that no one has wanted to touch it with a 3m pole :P.
> 
> > Considering the problem in the next larger context: why are we doing 
> > this at all?
> > 
> > Is this just so the generic fenv routines are chewed on as they contain 
> > the doc markup?  In which case it would be simpler to do that explicitly.
> > 
> > If it's so that a cpu- specific fenv doesn't need to provide all the 
> > objects, well, that could be done explicitly as well, I think?
> 
> assuming you're asking about the machine-override logic specifically and
> not "why am i changing the build system at all", then the current newlib
> design supports more than fenv.  fortunately, i believe i already wrote
> up all the docs you want :).  please give it a look and see if i missed
> anything.
> [1] https://sourceware.org/pipermail/newlib/2022/019275.html
> -mike

Ok, thanks, please push.


Corinna