[Bug 258463] x11/libwacom: Fix build with clang/lld 13

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=258463

--- Comment #6 from [email protected] ---
A commit in branch main references this bug:

URL:
https://cgit.FreeBSD.org/ports/commit/?id=a1edd535d35d03e2d54a49bffac39035b990a716

commit a1edd535d35d03e2d54a49bffac39035b990a716
Author:     Dimitry Andric <[email protected]>
AuthorDate: 2021-09-12 19:44:36 +0000
Commit:     Dimitry Andric <[email protected]>
CommitDate: 2021-10-02 10:58:25 +0000

    x11/libwacom: work around lld 13 no longer supporting symver tricks

    Though x11/libwacom was not yet built during the exp-run for clang/llvm
    13 (see bug 258209), due to some other dependencies not being available
    yet, I noticed that it failed to build with clang 13, or more
    specifically this is due to a behavior change in lld 13:

      ...
      [ 33% 10/30] cc  -o generate-hwdb generate-hwdb.p/tools_generate-hwdb.c.o
-Wl,--as-needed -Wl,--no-undefined -fstack-protector-strong -O2 -pipe -g
-fstack-protector-strong -fno-strict-aliasing '-Wl,-rpath,$ORIGIN/'
-Wl,-rpath-link,/wrkdirs/share/dim/ports/x11/libwacom/work/libwacom-1.5/_build/
-Wl,--start-group libwacom.so.2.6.1 /usr/local/lib/libglib-2.0.so
/usr/local/lib/libintl.so -Wl,--end-group
      [ 36% 11/30] /usr/local/bin/meson --internal exe --capture
65-libwacom.hwdb --
/wrkdirs/share/dim/ports/x11/libwacom/work/libwacom-1.5/_build/generate-hwdb
      FAILED: 65-libwacom.hwdb
      /usr/local/bin/meson --internal exe --capture 65-libwacom.hwdb --
/wrkdirs/share/dim/ports/x11/libwacom/work/libwacom-1.5/_build/generate-hwdb
      --- stderr ---

    Unfortunately the meson build process doesn't really show you why it
    failed, but it turns out that running the 'generate-hwdb' command
    segfaults:

      Starting program:
/wrkdirs/share/dim/ports/x11/libwacom/work/libwacom-1.5/_build/generate-hwdb

      Program received signal SIGSEGV, Segmentation fault.
      libwacom_add_match (device=device@entry=0x801031320, newmatch=0x0) at
../libwacom/libwacom.c:943
      943           device->matches[device->nmatches - 1] =
libwacom_match_ref(newmatch);
      (gdb) bt
      #0  libwacom_add_match (device=device@entry=0x801031320, newmatch=0x0) at
../libwacom/libwacom.c:943
      #1  0x000000080024fc7d in libwacom_matchstr_to_match
(device=device@entry=0x801031320, matchstr=<optimized out>) at
../libwacom/libwacom-database.c:207
      #2  0x000000080024e313 in libwacom_parse_tablet_keyfile (db=0x8010365a0,
datadir=0x200b70
"/wrkdirs/share/dim/ports/x11/libwacom/work/libwacom-1.5/data",
filename=<optimized out>) at ../libwacom/libwacom-database.c:652
      #3  load_tablet_files (db=0x8010365a0, datadir=0x200b70
"/wrkdirs/share/dim/ports/x11/libwacom/work/libwacom-1.5/data") at
../libwacom/libwacom-database.c:865
      #4  libwacom_database_new_for_path (datadir=0x200b70
"/wrkdirs/share/dim/ports/x11/libwacom/work/libwacom-1.5/data") at
../libwacom/libwacom-database.c:959
      #5  0x00000000002021b6 in main (argc=<optimized out>, argv=0x801036630)
at ../tools/generate-hwdb.c:131

    What happens is that an internal function 'libwacom_match_new' is
    supposed to be called, which returns a new 'WacomMatch' object. But
    instead, it calls a empty stub which returns NULL, resulting in this
    segfault. The empty stub was added as a rather nasty upstream hack to
    "Alias the accidentally exposed ABI into different functions", in
   
https://github.com/linuxwacom/libwacom/commit/b9961dbe912fa096230460b194eebdc8a590d256:

    > A special "trick" is used here to hide the ABI from new versions:
    > Usually when defining multiple versioned symbols, one would define one as
the
    > default one with @@
    >     .symver _foo1,foo@VERSION1
    >     .symver _foo2,foo@@version2 <-- default one

    > By leaving out the default one, ld doesn't know which one to link to and
    > fails with an unresolved symbol. rtld however can still figure it out, so
    > anything compiled will continue to work. This way we can make a symbol
    > disappear from the library for new builds but have old builds continue to
    > work with the new version.

    Unfortunately this trick/hack does not work anymore with lld 13, since
    https://github.com/llvm/llvm-project/commit/66d44304921, ("[ELF] Combine
    foo@v1 and foo with the same versionId if both are defined "). The idea
    behind the hack is to have the linker call the 'real' libwacom_match_new
    function whenever it is called from inside the library itself, but any
    external callers get the stubbed version which doesn't really do
    anything.

    I think libwacom should have used a different approach here, but just
    renaming those accidentally exposed internal functions to something
    different. Then the tricks with .symver are completely unnecessary. Here
    I added a patch that is as simple as possible, which adds #defines for
    two affected functions in libwacomint.h, renaming then from
    'libwacom_xxx' to 'libwacom_internal_xxx'. This does not affect the
    corresponding exposed functions in the libwacom.so, and makes the
    'generate-hwdb' command work OK again. I also ran the complete libwacom
    test suite, including the deprecated functions test, and it works fine.

    PR:             258463
    Approved by:    zeising (maintainer)
    MFH:            2021Q4

 x11/libwacom/files/patch-libwacom_libwacomint.h (new) | 12 ++++++++++++
 1 file changed, 12 insertions(+)

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