Linux-Modules Archive on lore.kernel.org
 help / color / Atom feed
From: Lucas De Marchi <lucas.demarchi@intel.com>
To: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: linux-modules@vger.kernel.org, Victor Stinner <victor.stinner@gmail.com>
Subject: Re: [PATCH kmod] Do not check for undefined symbols when building the Python modules
Date: Fri, 25 Oct 2019 15:07:22 -0700
Message-ID: <20191025220722.l7xe3lnrikcownvm@ldmartin-desk1.jf.intel.com> (raw)
In-Reply-To: <20191024174710.9441-1-thomas.petazzoni@bootlin.com>

On Thu, Oct 24, 2019 at 07:47:10PM +0200, Thomas Petazzoni wrote:
>kmod's configure.ac uses the -Wl,--no-undefined linker flag to verify
>at link time that all symbols of shared libraries are available, and
>that there are no undefined symbols.
>
>This make perfect sense for regular shared libraries. However, for
>Python extensions, which will be dlopen()ed inside the Python
>interpreter, it makes less sense.
>
>Since Python 3.8, there is a change in python-config script and
>Python's pkg-config file: it no longer links Python extensions with
>the libpython library. See
>https://docs.python.org/dev/whatsnew/3.8.html#debug-build-uses-the-same-abi-as-release-build
>which states:
>
>  On the other hand, pkg-config python3.8 --libs no longer contains
>  -lpython3.8. C extensions must not be linked to libpython (except on
>  Android and Cygwin, whose cases are handled by the script); this
>  change is backward incompatible on purpose. (Contributed by Victor
>  Stinner in bpo-36721.)
>
>So, when linking the kmod Python extensions, it currently fails with
>numerous unresolved symbols, that were previously provided by
>libpython:
>
>/home/test/autobuild/run/instance-3/output-1/host/opt/ext-toolchain/bin/../lib/gcc/powerpc64-buildroot-linux-gnu/7.4.0/../../../../powerpc64-buildroot-linux-gnu/bin/ld: libkmod/python/kmod/.libs/list_la-list.o: in function `__Pyx_PyObject_GetAttrStr':
>list.c:(.text.__Pyx_PyObject_GetAttrStr+0x48): undefined reference to `PyObject_GetAttr'
>/home/test/autobuild/run/instance-3/output-1/host/opt/ext-toolchain/bin/../lib/gcc/powerpc64-buildroot-linux-gnu/7.4.0/../../../../powerpc64-buildroot-linux-gnu/bin/ld: libkmod/python/kmod/.libs/list_la-list.o: in function `__pyx_tp_dealloc_4kmod_4list_ModListItem':
>list.c:(.text.__pyx_tp_dealloc_4kmod_4list_ModListItem+0x78): undefined reference to `PyObject_CallFinalizerFromDealloc'
>/home/test/autobuild/run/instance-3/output-1/host/opt/ext-toolchain/bin/../lib/gcc/powerpc64-buildroot-linux-gnu/7.4.0/../../../../powerpc64-buildroot-linux-gnu/bin/ld: libkmod/python/kmod/.libs/list_la-list.o: in function `__pyx_tp_dealloc_4kmod_4list_ModList':
>list.c:(.text.__pyx_tp_dealloc_4kmod_4list_ModList+0x30): undefined reference to `PyErr_Fetch'
>
>[Complete log at http://autobuild.buildroot.net/results/79a/79a5a0398723e8cfea0d0aa3dec5f7649aee4c63/build-end.log]
>
>Linking with libpython is no longer recommended: those symbols should
>remain unresolved in the Python extensions, as they wil be properly
>resolved when the Python extension gets loaded into the Python
>interpreter.
>
>Since we want to keep -Wl,--no-undefined globally in kmod, we leave
>the configure.ac file unchanged, and instead, specifically in the
>LDFLAGS used to build the Python extensions, we override
>-Wl,--no-undefined with -Wl,-z,undefs. Ideally, -Wl,--no-undefined is
>the same as -Wl,-z,defs, and the effect of these options can be
>canceled on the linker command line by a following -Wl,-z,undefs (see
>the ld man page for details).
>
>Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
>Cc: Victor Stinner <victor.stinner@gmail.com>

applied, thanks

Lucas De Marchi

>---
> Makefile.am | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/Makefile.am b/Makefile.am
>index c5c2f06..8e9c90d 100644
>--- a/Makefile.am
>+++ b/Makefile.am
>@@ -173,7 +173,7 @@ CPYTHON_MODULE_CFLAGS = \
> 	$(AM_CFLAGS) -DCPYTHON_COMPILING_IN_PYPY=0 \
> 	$(PYTHON_NOWARN) $(PYTHON_CFLAGS) \
> 	-fvisibility=default
>-CPYTHON_MODULE_LDFLAGS = $(AM_LDFLAGS) -module -avoid-version -shared
>+CPYTHON_MODULE_LDFLAGS = $(AM_LDFLAGS) -module -avoid-version -shared -Wl,-z,undefs
>
> if BUILD_PYTHON
> pkgpyexec_LTLIBRARIES = \
>-- 
>2.21.0
>

      reply index

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-24 17:47 Thomas Petazzoni
2019-10-25 22:07 ` Lucas De Marchi [this message]

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191025220722.l7xe3lnrikcownvm@ldmartin-desk1.jf.intel.com \
    --to=lucas.demarchi@intel.com \
    --cc=linux-modules@vger.kernel.org \
    --cc=thomas.petazzoni@bootlin.com \
    --cc=victor.stinner@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Modules Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-modules/0 linux-modules/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-modules linux-modules/ https://lore.kernel.org/linux-modules \
		linux-modules@vger.kernel.org
	public-inbox-index linux-modules

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-modules


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git