Bug 17375 – colliding modules detected with binutils 2.28 linker and shared libraries

Happens with shared libraries on Arch Linux w/ binutils 2.28. Apparently copy relocated moduleinfos now end up as data symbols instead of bss.

On Arch Linux, this is reproducible with binutils 2.28.0, but not reproducible with 2.27.

Bisecting binutils points to: 9acc85a62eb76c270724bba15c889d2d05567b6a is the first bad commit commit 9acc85a62eb76c270724bba15c889d2d05567b6a Author: Alan Modra <[email protected]> Date: Wed Dec 28 17:04:15 2016 +1030 Use dynrelro for symbols in relro sections too PR ld/20995 bfd/ * elflink.c (elf_link_add_object_symbols): Mark relro sections in dynamic objects SEC_READONLY. ld/ * testsuite/ld-elf/pr20995c.s: New test file. * testsuite/ld-elf/pr20995-2so.r: Likewise. * testsuite/ld-elf/elf.exp: Run it. :040000 040000 decd212336814caf0562835700a42a8f6d3e5e34 8f7d306bf5df00e27fa208f6dc66e345ca5064e8 M bfd :040000 040000 c101f8812c1c65893d81807818e3bfb8acd3ae1e decd54f18574d1b7d39c8888ff551cbde3d3cbe0 M ld

Also see https://sourceware.org/bugzilla/show_bug.cgi?id=20995 and http://sourceware-org.1504.n7.nabble.com/dynrelro-section-for-read-only-dynamic-symbols-copied-into-executable-td429858.html for more info on the binutils change. As a workaround, also compile the executable with -fPIC (PIE). This will avoid the necessity for copy relocation. We made PIE the default in a recent release.

Workaround for Arch Linux: Grab the 2.27 package from https://archive.archlinux.org/packages/b/binutils/binutils-2.27-1-x86_64.pkg.tar.xz, unpack it somewhere, then prefix $PATH with that package's "bin" directory and $LD_LIBRARY_PATH with that package's "lib" directory.

The PIE (-fPIC) workaround seems a lot simpler. It should be made default on Arch anyhow after we've switched with 2.072.2 http://forum.dlang.org/post/[email protected].

(In reply to Martin Nowak from comment #5) > The PIE (-fPIC) workaround seems a lot simpler. Sorry, yeah, I meant when modifying the build command is not feasible (e.g. when bisecting / doing regression testing). Do you think you could submit a PR to fix the Druntime and Phobos Makefiles? I'd also like to make Digger apply that patch automatically so it's possible to run tests of older versions of D with newer binutils.

Maybe you had a different git repo, my bisect ended at commit https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=9acc85a62eb76c270724bba15c889d2d05567b6a. We could solve this by emitting the ModuleInfos themselves (not only a pointer to them) to their own sections and using the old section bracket trick (__start_minfo and __stop_minfo see https://github.com/dlang/dmd/blob/eb3bc8d8902a0b0c3b3b02058265d811ec310eb9/src/ddmd/backend/elfobj.c#L3319). Would need 2 sections if some of them are readonly and some are relro though.

(In reply to Martin Nowak from comment #7) > Maybe you had a different git repo, my bisect ended at commit > https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git; > h=9acc85a62eb76c270724bba15c889d2d05567b6a. No idea what you mean; that's the same commit I mentioned in comment 2 above.

> It should be made default on Arch anyhow after we've switched with 2.072.2 Sadly it's not the default on Arch yet, see e.g. http://forum.dlang.org/post/[email protected] and my proposal to make it default for all Posix distros: https://github.com/dlang/phobos/pull/5586

Had the same problem with binutils 2.28 and dmd 2.075.0 on NixOS with druntime and phobos. Working around the problem as suggested with make -f posix.mak PIC=-fPIC INSTALL_DIR=$out DMD=$DMD works for phobos. But for druntime I needed to patch a Makefile, substituteInPlace druntime/test/common.mak \ --replace "DFLAGS:=" "DFLAGS:=-fPIC " otherwise the link test in the druntime unittests would fail when running with make -f posix.mak unittest PIC=-fPIC DMD=$DMD BUILD=release

Commits pushed to master at https://github.com/dlang/phobos https://github.com/dlang/phobos/commit/3d36e434b84cf6ebd7341aaffe2b3b0b588a0262 Issue 17375 - use -fPIC by default for Phobos on Posix This also fixes: Fix Issue 17107 - Running phobos unittests do not work with PIE https://github.com/dlang/phobos/commit/d400af081aad1dcb735170a99f9f8d1562788db9 Merge pull request #5586 from wilzbach/fpic-by-default Issue 17375 - use -fPIC by default for Phobos on Posix

Commits pushed to stable at https://github.com/dlang/phobos https://github.com/dlang/phobos/commit/3d36e434b84cf6ebd7341aaffe2b3b0b588a0262 Issue 17375 - use -fPIC by default for Phobos on Posix https://github.com/dlang/phobos/commit/d400af081aad1dcb735170a99f9f8d1562788db9 Merge pull request #5586 from wilzbach/fpic-by-default

The colliding module detection has been removed: https://github.com/dlang/druntime/pull/1921

If that detection has been removed, does this mean we can revert to compiling without -fPIC again? It's slows down code on x86. I put it in dmd.conf for Gentoo by default, because shared libraries would not load due to this bug. So can we revert to the pre binutils 2.28 procedures now for druntime, Phobos, dmd.conf?

-fPIC is only the default for x86_64 on Linux and required due to PIE hardening on many distributions.