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Re: Ping Re: Fix IBM long double spurious overflows
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: David Edelsohn <dje dot gcc at gmail dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>
- Date: Wed, 29 Jan 2014 03:59:36 +0000
- Subject: Re: Ping Re: Fix IBM long double spurious overflows
- Authentication-results: sourceware.org; auth=none
- References: <Pine dot LNX dot 4 dot 64 dot 1401041314430 dot 23651 at digraph dot polyomino dot org dot uk> <CAGWvnykMLF=xsWKpw+rv3HyRCSH0ZDCPmin8J+RWE9x5d-HA6A at mail dot gmail dot com> <Pine dot LNX dot 4 dot 64 dot 1401281749340 dot 30131 at digraph dot polyomino dot org dot uk> <CAGWvnynQAsdBtK8ewqowY4F=Dq1FhNWj2WKj9p42khsE2cKmwA at mail dot gmail dot com> <Pine dot LNX dot 4 dot 64 dot 1401282108420 dot 2449 at digraph dot polyomino dot org dot uk> <CAGWvnym6pU_0U03zcPRubzr0u3gADtrdHC4Cj54wf_J=Y-5o3g at mail dot gmail dot com> <Pine dot LNX dot 4 dot 64 dot 1401290308361 dot 2449 at digraph dot polyomino dot org dot uk>
On Wed, 29 Jan 2014, Joseph S. Myers wrote:
> It is appropriate for glibc maintainers to seek consensus in the glibc
> community on minimum requirements for glibc ports, just as on any other
> question about what is or is not supported in glibc. For example, it is
> presently expected that a port uses ELF and supports TLS and PIC. What
> floating-point formats are supported is part of that.
>
> I'll seek consensus in the glibc community on minimum standards for the
> underlying floating-point arithmetic.
I have now made my proposal at
<https://sourceware.org/ml/libc-alpha/2014-01/msg00582.html>. This is
similar to plenty of other proposals in glibc (such as those I made
recently regarding principles for moving architectures from ports to libc,
or regarding increasing the minimum Linux kernel version).
As the de facto maintainer for the soft-float powerpc support in glibc, I
get to deal with these test failures when reviewing test results each
release cycle, and they take a disproportionate amount of time, and my
view is that fixing these issues in the __gcc_* functions, in copies local
to glibc if necessary, is the best way to keep the ldbl-128ibm support in
glibc maintainable. (Although I'd certainly prefer to have suitable
versions of the functions in libgcc, under different names and only
enabled with options such as -frounding-math if necessary - although
enabling correctness for exceptions with -frounding-math would seem rather
odd.)
glibc used not to require TLS or atomic operations beyond test-and-set;
the non-TLS support became unmaintainable, and now it does require TLS
(which required kernel heleprs to be implemented on various architectures,
and did make things slower for some architectures on some workloads). It
used not to require a 2.6 kernel when used with the Linux kernel; now it
requires 2.6.16 and we're considering requiring 2.6.32. I think of
requirements on the floating point used by glibc functions in much the
same way: evaluating a new requirement that would help in maintaining and
developing glibc.
--
Joseph S. Myers
joseph@codesourcery.com