Michael Felt added the comment:
In https://bugs.python.org/issue26439 I have been working on this for AIX - as
the default behavior was to depend on two things:
a) ldconfig -p (which generally does not exist on AIX, and I doubt it will know
about the non-gnu libraries
b) that the objects are files rather than members of an archive
For python cdll() to work (as find_library generally did not) - the work-around
was to extract archive members into standard directories and/or hard-code
unique AIX names. But again, always as files, as CDLL did not modify the
dlopen() mode to permit loading a shared library from an archive.
re: this issue and behavioral differences between find_library and cdll()
(rather dlopen()) searches - a linker is different from a dlopen. When
compiling an argument such as -lc -- on AIX -- tells the linker to look in
libc.a for any member (of the right size) that satisfies an unknown symbol.
That archive (base) and member (member) name is remembered in the "loader
section" during linking. Note that static members have no loader section of
their own, nor do they add one to the object (program or shared library) being
linked.
As a compatibility feature - when a member is not found in an archive the AIX
rtl (run-time-linker) also looks for a file named libFOO.so (e.g., libc.so) -
this grace behavior is why CDLL() has worked somewhat using default behavior in
Lib/ctypes.
As to LD_LIBRARY_PATH and LIBPATH. In AIX terms, these are environment
variables to supplement the library search path - only when no PATH information
is provided (i.e., cdll("./libc.so") will only look in the current directory of
the process, and only for the file libc.so)
The default search path is a list of the directories used to link the
executable (e.g., python). For me that list is:
***Import File Strings***
INDEX PATH BASE MEMBER
0 /usr/vac/lib:/usr/lib:/lib
In other words, python, by default, is only going to look in very standard
locations - even though it knows it's prefix is not /usr.
There are two solutions - and I will make changes as appropriate.
a) automate setting an environment variable if it is not already set to
something like
_os.environ['LIBPATH'] = "%s/lib" % _sys.prefix
and not something "arbitrary" such as /usr/local/lib
b) modify the LDFLAGS when packaging to include
-L${prefix}/lib which will have the effect of changing the default search path
via -W,-blibpath=/usr/vac/lib:/usr/lib:/lib:${prefix}/lib
In any case, in my patch for AIX in ctypes the two will work identical (cdll()
even calls aix.find_library() to simplify portability between GNU/posix
environments that expect or support only filenames to work with AIX archive
packaging.
My apologies for the wall of text. This is not a simple subject.
----------
nosy: +Michael.Felt
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<http://bugs.python.org/issue9998>
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