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

From: Sergey Bugaev
Subject: Re: [VERY RFC PATCH 2/2] hurd: Make it possible to call memcpy very early
Date: Fri, 21 Apr 2023 12:27:24 +0300


On Thu, Apr 20, 2023 at 11:38 PM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
> Can't you use a similar strategy done by 
> 5355f9ca7b10183ce06e8a18003ba30f43774858 ?

Do I understand it right that that is the moral equivalent of

#define memcpy __memcpy_sse2_unaligned

except that it works aat assembly level and so will catch implicit
calls to memcpy that the compiler may insert?

Assuming for a second that we don't care about implicit memcpys (but
we should) and only about the explicit one made by the MIG runtime, we
could maybe even just do

 void *
 __mig_memcpy (void *dst, const void *src, vm_size_t len)
-  return memcpy (dst, src, len);
+  return __memcpy_sse2_unaligned (dst, src, len);

but that (as well as your proposal) would make *all* calls to memcpy
in this place go through the baseline version, even after the early
startup is done. Whereas my proposal attempted to avoid that -- unless
of course H.J. is right and this prevents the indirect relocation from
replacing the function pointer later, in which case it's even worse
because it would sabotage memcpy for the whole program and not just a
couple of files.


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