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Message-ID: <20150528114437.GK20259@port70.net>
Date: Thu, 28 May 2015 13:45:15 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: Progress since 1.1.9
* Rich Felker <dalias@...c.org> [2015-05-27 19:13:08 -0400]:
> The one roadmap item I don't have any progress on is what to do with
> the libgcc_s symbol version mess, and I think we should probably just
> hold off until the next release cycle for that now.
in case anyone wonders about the issue:
libgcc_s has a symbolic reference to an internal deprecated
symbol with no default version on x86 (in gcc trunk).
(so no @version only @@version which makes it invisible to
musl and ld).
the deprecated function is a constructor in libgcc_s that
initializes an unused struct in libgcc_s.
the only reason the symbol got versioned this way is because
they want old binaries to work and remove the symbol from
libgcc_s for new binaries, while still using the same symbol
name in new binaries but with different abi behaviour: now
it's only available in libgcc.a to fix their ifunc hack for
multi-versioning.
since it's a symbol internal to libgcc and the semantics
of the symbol changed they could have just used a new name
and left the old one alone (so old stuff is guaranteed to not
break including musl and new binaries use the new symbol with
new semantics).
so i still think my proposed libgcc patch makes more sense
than versioning:
https://gcc.gnu.org/ml/gcc-patches/2015-05/msg00899.html
gcc is unlikely to fix this, but this is a nonsense usecase
(and there is no other known use of versioning that is broken
with musl.. in theory other libs may deprecate symbols in a
similar way while still keeping symbolic references to them,
but such use was not yet observed).
in musl-gcc it can be worked around by preloading a noop
__cpu_indicator_init and in a musl based gcc it can be
patched out.
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