Re: [VERY RFC PATCH 2/2] hurd: Make it possible to call memcpy very early

[Sergey Bugaev]

On Fri, Apr 21, 2023 at 3:58 PM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
> > Yes, sure, I wasn't really suggesting we do that change. My point is,
> > I would like to make the same memcpy callsites both work during early
> > startup and start calling the more efficient implementation once early
> > startup is done -- if that's possible.
>
> That's the whole idea of dl-symbol-redir-ifunc.h, since it is explicit
> enable by TU.

Then I must be misunderstanding how dl-symbol-redir-ifunc.h works
(please explain!),

because I don't see how it would achieve that. Doesn't it change all
memcpy calls in the current translation unit (.c file) to always call
the baseline memcpy -- not only during startup, but even after the
startup has been completed?

To be clear, this is about memcpy calls made *during* very early
startup, yes, but not *in* some special startup-only code (like
init-first.c and hurdstartup.c for instance): that startup-specific
code calls into the fairly generic code (mig_memcpy.c and the various
MIG-generated RPC routines) that is used both during this very early
startup and then much later during the normal runtime, and *that's*
what calls memcpy. I'd like for memcpy calls in that generic code to
both work during early startup and use the efficient memcpy
implementation later. If dl-symbol-redir-ifunc.h can achieve that,
please help me understand how.

Sergey