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Re: Distributions still suffering from s390 ABI change problems.
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: David Miller <davem at davemloft dot net>, "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: krebbel at linux dot vnet dot ibm dot com, roland at hack dot frob dot com, aurelien at aurel32 dot net, siddhesh at redhat dot com, allan at archlinux dot org, libc-alpha at sourceware dot org
- Date: Tue, 15 Jul 2014 02:12:15 -0400
- Subject: Re: Distributions still suffering from s390 ABI change problems.
- Authentication-results: sourceware.org; auth=none
- References: <53C43A5E dot 9020304 at redhat dot com> <20140714 dot 132444 dot 140785163900092398 dot davem at davemloft dot net> <53C440FF dot 3010308 at redhat dot com> <20140714 dot 140948 dot 808129071568411651 dot davem at davemloft dot net>
On 07/14/2014 05:09 PM, David Miller wrote:
> Therefore, on the negative side, we might be stuck with this. But, on
> the positive side, we can refer to this incident next time a similar
> incident arises. We now know exactly what the ramifications are for
> not handling this properly.
OK, so I just tried a SO name bump on x86-64 and all hell breaks loose.
It's unsupportable as a solution for glibc.
The SO name bump in a mixed-ABI environment like debian results in two
libc's being loaded and competing for effectively the same namespace
of symbols with resolution (and therefore selection of the ABI) being
determined by ELF interposition and scope rules. It's a nightmare.
It's possible a worse solution than just telling everyone to rebuild
and get on with their lives.
Should we have done something like this instead:
* Add an s390 .gnu.attributes tag for the jmp_buf ABI change.
* Enforce the ABI at the linker level so you can't link old and
new objects, like is done by ARM with hard vs. soft fp.
* Make .gnu.attributes loadable (SEC_ALLOC) like proposed once
by H.J. and put it somewhere with other loaded read-only
data (minimize mmap calls).
* Have the dynamic loader do a check as it loads objects to
ensure their ABI matches via an s390 specific function that
knows which .gnu.attributes are ABI special and compares them
to the presently assembled ABI (a little extra execute code
per DSO load).
Thoughts?
Several people have been considering extended .gnu.attributes
to the dynamic loader, but there wasn't any real impetus,
perhaps until now.
Cheers,
Carlos.