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Re: glibc 2.21 - Machine maintainers, please test your machines.
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>, Chris Metcalf <cmetcalf at ezchip dot com>
- Cc: Torvald Riegel <triegel at redhat dot com>, GNU C Library <libc-alpha at sourceware dot org>, David Miller <davem at davemloft dot net>, Richard Henderson <rth at redhat dot com>, Mike Frysinger <vapier at gentoo dot org>, Andreas Schwab <schwab at suse dot de>, "Joseph S. Myers" <joseph at codesourcery dot com>, Kaz Kojima <kkojima at rr dot iij4u dot or dot jp>, Thomas Schwinge <thomas at codesourcery dot com>, Marcus Shawcroft <marcus dot shawcroft at linaro dot org>, Chung-Lin Tang <chunglin_tang at mentor dot com>, Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>, Andreas Krebbel <krebbel at linux dot vnet dot ibm dot com>
- Date: Mon, 26 Jan 2015 23:17:22 -0500
- Subject: Re: glibc 2.21 - Machine maintainers, please test your machines.
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On 01/25/2015 06:05 PM, H.J. Lu wrote:
> On Sun, Jan 25, 2015 at 2:10 PM, Chris Metcalf <cmetcalf@ezchip.com> wrote:
>> On 1/25/2015 4:51 PM, H.J. Lu wrote:
>>
>>> This is for x86. Each target can do something like it if needed.
>>
>>
>> This does change the ABI for existing code, however, which may legitimately
>> have sem_t objects that are only aligned to 4-byte boundaries. Your change
>> is a good idea for new platforms. I suppose we could also do something
>> with symbol versioning to use it for existing 32-bit platforms with
>> 64-bit atomics, too. So there seem to be multiple fixes we can consider.
>>
>
> It doesn't change the size, only increases alignment from 4 bytes to 8 bytes.
> It may not work on all targets. It works for x32.
How can you change the alignment?
That will break applications that embedded a sem_t in other structures by
changing the size of those structures as they expand to account for the
changed object alignment?
Cheers,
Carlos.