Bug 7224 - glibc in build system is older than our requirement
: glibc in build system is older than our requirement
: ThinLinc
Build system
: trunk
: PC Unknown
: P2 Normal
: 4.10.0
Assigned To:
: 5241
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Reported: 2018-08-15 12:45 by
Modified: 2018-09-13 16:02 (History)
Acceptance Criteria:
* glibc version for all archs should be the same as our documented requirements * Jenkins rebuild of cenbuild should work * workarounds for old glibc versions should be removed



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Description From cendio 2018-08-15 12:45:14
On bug 5754, we raised the glibc requirement to 2.12. However, we didn't
actually change anything in our build system, which uses several old versions:


Motivation for upgrade:

1) To avoid that we are using different glibc versions on different platforms.
We could use 2.12 on all.

2) As mentioned on bug 5754, "It will probably also solve various minor
annoyances", which might mean getting rid of workarounds we have today.

3) Reduce the risk of subtle bugs and reduced functionality - we are using a
glibc version which is no longer common.

4) Performance. If we just consider x86_64, these performance related
enhancements are listed between 2.5 and 2.12:

* New optimized string functions for x86-64: strstr, strcasestr, memcmp,
  strcspn, strpbrk, strspn, strcpy, stpcpy, strncpy, strcmp (SSE2, SSE4.2),
  strncmp (SSE2, SSE4.2), strchr (SSE4.2), strrchr (SSE4.2).
  Contributed by H.J. Lu.

  strlen, rawmemchr, strcmp (SSSE3), strncmp (SSSE3).
  Implemented by Ulrich Drepper.

* Faster strlen, strchr, strchrnul, strrchr, memchr, and rawmemchr for x86-64.
  Implemented by Ulrich Drepper.

* New implementation of memmem, strstr, and strcasestr which is O(n).
  Implemented by Eric Blake.

* Faster memset for x86-64.

On one hand, for functions which does not change ABI (does not use symbol
versioning) and are not inlined, one "should" get the performance improvement
just by using a modern glibc at runtime. It does not matter that old headers
are used. However, apparently inlined functions are sometimes used. From

glibc has special string functions that are faster than the normal library
functions. Some of the functions are additionally implemented as inline
functions and others as macros. This might lead to problems with existing codes
but it is explicitly allowed by ISO C.

The optimized string functions are only used when compiling with optimizations
(-O1 or higher).
------- Comment #12 From cendio 2018-09-10 09:38:28 -------
Jenkins builds are passing again.
------- Comment #13 From cendio 2018-09-10 09:40:04 -------
r33650 fixed the cdrtools build, which falled apart with a high number of make
------- Comment #14 From cendio 2018-09-13 16:02:27 -------
> * glibc version for all archs should be the same as our documented requirements

We do indeed run glibc 2.12.2 everywhere.

(The requirement is for 2.12.0, but 2.12.2 is the same ABI, but with some
internal bug fixes.)

> * Jenkins rebuild of cenbuild should work


> * workarounds for old glibc versions should be removed

I can not find any references to workarounds for glibc.