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Date: Tue, 10 Mar 2015 09:30:44 +0100
From: Jens Gustedt <jens.gustedt@...ia.fr>
To: musl@...ts.openwall.com
Subject: Re: pthread object sizes for new archs
Hello,
Am Montag, den 09.03.2015, 21:07 -0400 schrieb Rich Felker:
> How does this affect "glibc ABI compatibility"? Very little. As long
> as the sizes of the musl types are no larger than the sizes of the
> glibc types on the same arch, compatibility with glibc binary code
> (apps or libs) is not affected. All that is affected if the ABI of
> third-party libraries that use pthread types as members of public
> structs, and it only matters if you're calling such libraries using
> the glibc-derived ABI from code compiled against musl and using the
> affected structures. This is a very unusual usage case, not something
> we've ever prioritized supporting (it's broken in several other ways
> anyway, or at least it was historically), and IMO it's not worth
> severely bloating new archs that people actually want to use.
So to rephrase your arguments for that
- For the case I compile my code with the glibc ABI and link it with
musl: any struct that has pthread (or C11 thread) components in it
will potentially only use a smaller part of that pthread (C11)
component. In particular in that case when compiling with the glibc
ABI the compiler always generates a consistent offset for the
pthread components. Sounds ok.
But this only works because the glibc ABI doesn't export any
interface that has a visible combination of different pthread
components. Are we sure about that?
- For the case that I compile code with the musl ABI and link it with
glibc, this may (and probably will) cause out-of-bounds errors on
execution. I would very much prefer that big warnings are already
issued when doing such a link, or even better if such a link would
fail systematically.
I hope that there is nobody out there, who would be currently using
this model, perhaps unknowingly.
Jens
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