[Xcb] [PATCH pthread-stubs 0/4] Rework pthread-stubs design/implementation

Emil Velikov emil.l.velikov at gmail.com
Thu Nov 3 20:24:55 UTC 2016

Hi all,

A recent change (commit fa6db2f9c01 - list.m4: Add some new pthread symbols)
lead to an interesting bugreport [1] which makes me think that the current
pthread-stubs design isn't as robust (broken?) as one would expect.

In brief: if there is a pthread-stubs library, one can end up using a
mismatched API - if one uses dlopen with a binary which pulls a full pthreads
implementation. That is because the weak symbols, as provided by the
pthread-stubs DSO, get overridden.

This has gone unnoticed because a) on most platforms pthread-stubs never
creates a DSO and in the rare case where it does b) it's very uncommon to
dlopen a binary which pulls a non-lightweight pthreads symbols, from a
pthreads-stubs (linked) one.

The only solutions that I can think of are:
 1) make pthread-stubs "meta package" who's Cflags/Libs expand to the platform
specific PTHREAD_{CFLAGS,LIBS} if the runtime does not provide lightweight
pthread symbols, or
 2) "kill off" pthread-stubs and let everyone
 - handle the "do I need to link against pthreads or not" in their configure.ac
 - link against the complete/full pthread API

Imho 2) is rather selfish/overzealous so I've went ahead and tackled 1).

Note: 1/4 a standalone fix which can be applied independently of how the
direction/discussions reached.

The remaining patches can be squashed or kept separate, based on how things go.


Cc: Rob Clark <robclark at freedesktop.org>
Cc: Ben Widawsky <ben at bwidawsk.net>
Cc: Uli Schlachter <psychon at znc.in>
Cc: Josh Triplett <josh at freedesktop.org>
Cc: Jamey Sharp <jamey at minilop.net>

[1] https://bugs.freedesktop.org/show_bug.cgi?id=98048

Emil Velikov (4):
  autogen.sh: quote path variables
  Revert "list.m4: Add some new pthread symbols"
  Rework the pthread-stub design
  configure: drop various AC_macros

 Makefile.am         |  10 --
 README              |  33 +++-
 autogen.sh          |   6 +-
 configure.ac        |  69 ++++----
 list.m4             |   3 -
 m4/ax_pthread.m4    | 485 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 pthread-stubs.pc.in |   3 +-
 stubs.c.m4          |  91 ----------
 8 files changed, 548 insertions(+), 152 deletions(-)
 create mode 100644 m4/ax_pthread.m4
 delete mode 100644 stubs.c.m4


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