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Pedro Alves a4a1c15754 Fix PR gdb/16818, workaround Python's forcing of -export-dynamic
GDB's use of --dynamic-list to only export the proc-service symbols is
broken due to Python's "python-config --ldflags" saying we should link
with -export-dynamic, causing us to export _all_ extern symbols
anyway.  On Fedora 23:

 $ python-config --ldflags
 -lpython2.7 -lpthread -ldl -lutil -lm -Xlinker -export-dynamic
 $ python3.4-config --ldflags
  -L/usr/lib64 -lpython3.4m -lpthread -ldl  -lutil -lm  -Xlinker -export-dynamic

Having GDB export all its symbols leads to issues such as PR gdb/16818
(GDB crashes when using name for target remote hostname:port), where a
GDB symbol unintentionally preempts a symbol in one of the NSS modules
glibc loads into the process.  NSS modules should not define symbols
outside the implementation namespace or the relevant standards, but,
alas, that's a longstanding and hard to fix issue.  See libc-alpha
discussion at:

  [symbol name space issues with NSS modules]
  https://sourceware.org/ml/libc-alpha/2016-04/msg00130.html

Python should instead be either using GCC's symbol visibility feature
or -Wl,--dynamic-list as well, to only export Python API symbols, but,
it doesn't.  There are bugs open upstream for that:

  [Use -Wl,--dynamic-list=x.list, not -Xlinker -export-dynamic]
  http://bugs.python.org/issue10112

  [Use GCC visibility attrs in PyAPI_*]
  http://bugs.python.org/issue11410

But that's taking a long while to resolve.

I thought of working around this Python issue by making GDB build with
-fvisibility=hidden, as Jan suggests in Python issue 10112, as then
Python's "-Xlinker -export-dynamic" has no effect.  However, that
would need to be done in the whole source tree (bfd, libiberty, etc.),
and I think that would break GCC plugins, as I believe those have
access to all of GCCs symbols, by "design".  So we'd need a new
configure switch, or have the libraries in the tree detect which of
GCC or GDB is being built, but that doesn't work, because the answer
can be "both" with combined builds...

So this patch instead works around Python's bug, by simply sed'ing
away "-Xlinker -export-dynamic" from the result of python-config.py
--ldflags, making -Wl,--dynamic-list work again as it used to.  It's
ugly, but so is the bug...

Note that if -Wl,--dynamic-list doesn't work, we always link with
-rdynamic, so static Python should still work.

Tested on F23 with --python=python (Python 2.7) and
--python=python3.4.

gdb/ChangeLog:y
2016-05-03  Pedro Alves  <palves@redhat.com>

	* configure.ac (PYTHON_LIBS): Sed away "-Xlinker -export-dynamic".
	* configure: Regenerate.
2016-05-03 10:31:22 +01:00
bfd Automatic date update in version.in 2016-05-03 00:00:09 +00:00
binutils Enhance readelf's recognition of AVR relocation types. 2016-04-29 14:05:12 +01:00
config
cpu
elfcpp
etc
gas Provide xmemdup0 2016-04-27 17:07:17 +09:30
gdb Fix PR gdb/16818, workaround Python's forcing of -export-dynamic 2016-05-03 10:31:22 +01:00
gold Updated Chinese (simplified) translations for bfd, binutils and gold. 2016-04-28 14:09:49 +01:00
gprof update many old style function definitions 2016-04-20 07:04:49 -04:00
include Add support to AArch64 disassembler for verifying instructions. Add verifier for LDPSW. 2016-04-28 09:11:03 +01:00
intl
ld Download source only on remote host 2016-04-29 06:52:55 -07:00
libdecnumber
libiberty
opcodes Add support to AArch64 disassembler for verifying instructions. Add verifier for LDPSW. 2016-04-28 09:11:03 +01:00
readline
sim Fix a typo in the check for SNANs in the RX simulator. 2016-04-27 12:37:11 +01:00
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		   README for GNU development tools

This directory contains various GNU compilers, assemblers, linkers, 
debuggers, etc., plus their support routines, definitions, and documentation.

If you are receiving this as part of a GDB release, see the file gdb/README.
If with a binutils release, see binutils/README;  if with a libg++ release,
see libg++/README, etc.  That'll give you info about this
package -- supported targets, how to use it, how to report bugs, etc.

It is now possible to automatically configure and build a variety of
tools with one command.  To build all of the tools contained herein,
run the ``configure'' script here, e.g.:

	./configure 
	make

To install them (by default in /usr/local/bin, /usr/local/lib, etc),
then do:
	make install

(If the configure script can't determine your type of computer, give it
the name as an argument, for instance ``./configure sun4''.  You can
use the script ``config.sub'' to test whether a name is recognized; if
it is, config.sub translates it to a triplet specifying CPU, vendor,
and OS.)

If you have more than one compiler on your system, it is often best to
explicitly set CC in the environment before running configure, and to
also set CC when running make.  For example (assuming sh/bash/ksh):

	CC=gcc ./configure
	make

A similar example using csh:

	setenv CC gcc
	./configure
	make

Much of the code and documentation enclosed is copyright by
the Free Software Foundation, Inc.  See the file COPYING or
COPYING.LIB in the various directories, for a description of the
GNU General Public License terms under which you can copy the files.

REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info
on where and how to report problems.