Fixing the glibc adobe flash incompatibility

[Hans de Goede]

Hi all,

For those who do not know it yet, recent Fedora glibc updates include
an optimized memcpy (which gets used on some processors) which breaks the
64 bit adobe flash plugin.

The problem has been analyzed and is known, as well as a fix for it, see:
https://bugzilla.redhat.com/show_bug.cgi?id=638477

The problem still exists however. The glibc developers say that this is
not a glibc bug, but a flash plugin bug. And technically they are 100%
correct, and the adobe flash plugin is a buggy .... (no surprise there).
To be specific the flash plugin is doing overlapping memcpy-s which is
clearly not how memcpy is supposed to be used. But the way the flash
plugin does overlapping memcpy's happens to work fine as long as one as
the c library does the memcpy-s in forward direction. And the new memcpy
implementation does the memcpy in backward direction.

The glibc developers being technically 100% correct is not helping our
end users in this case though. So we (The Fedora project) need to come up
with a solution to help our end users, many of whom want to use the adobe
flash plugin.

This solution could be reverting the problem causing glibc change, or
maybe changing it to do forward memcpy's while still using the new SSE
instructions, or something more specific to the flash plugin, as long
as it will automatically fix things with a yum upgrade without requiring
any further user intervention.

I would also like to point out that if this were to happen in Ubuntu
which we sometimes look at jealously for getting more attention / users
then us, the glibc change would likely be reverted immediately, as that
is the right thing to do from an end user pov.

I've filed a ticket for FESCo to look into this, as I believe this
makes us look really bad, and the glibc maintainers do not seem to be
willing to fix it without some sort of intervention:
https://fedorahosted.org/fesco/ticket/501

Regards,

Hans