fix(compat.glx-runtime): ln -sf was last-wins, and nothing checked the ABI (mcpp#352) - #177
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…the ABI (mcpp#352)
On Fedora 44 this package produced
libGLX.so.0 -> /usr/lib/libGLX.so.0 # 32-bit
libOpenGL.so.0 -> /usr/lib64/libOpenGL.so.0
and the application died with `libGLX.so.0: wrong ELF class: ELFCLASS32`,
surfacing as a silent exit code 255 with no output at all.
THE OBVIOUS DIAGNOSIS IS NOT THE BUG. The issue reads this as "generated
assuming the Debian layout", but `/usr/lib64` is already ahead of `/usr/lib` in
`candidate_dirs()`. Two other things were wrong:
1. **`ln -sf` overwrites.** The loop reached /usr/lib64 first and linked the
correct file, then reached /usr/lib and replaced it. Last-wins, not
first-wins. `libOpenGL.so.0` survived as 64-bit only because that host's
32-bit glvnd does not ship it -- which is why exactly one link in the bug
report was right, and that is evidence rather than coincidence.
2. **No ABI check anywhere**, including in `required`, which asserted that
libGLX.so.0 and libGL.so.1 EXIST. Both existed. Both were 32-bit. So the
package reported success.
There is no layout to assume, which is why a better ordering is not the fix: the
FHS biarch clause makes /usr/lib 32-bit (Fedora/RHEL/SUSE), Debian explicitly
declined that clause and uses /usr/lib/<triplet> so its /usr/lib is 64-bit, and
Arch is a third answer again. An ABI check makes the order stop mattering.
So: enumerate and decide per file (first-wins, keyed by soname), read
e_ident[EI_CLASS] out of the file itself -- five bytes, no external tool, because
`file`/`readelf` may not be installed when a hook runs -- and make `required`
assert 64-bit rather than merely present. Both failure paths now name the cause
and what to install.
Verified against a forged biarch host (32-bit libGLX.so.0 in /usr/lib, the real
one in /usr/lib64): both required links resolve to /usr/lib64 and both are
ELF64. The same fixture under the old loop lands on /usr/lib.
The same three rules -- ask the loader, check the ABI, first hit wins -- are now
one shared module in the xlings index (libs/hostlib.lua), where four call sites
had four answers and three were wrong.
Refs: mcpp-community/mcpp#352
Design: openxlings/xlings .agents/docs/2026-08-07-graphics-experience-industry-survey-and-plan.md §8.1, §9.2
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deploy-site and refresh-site-cache both checked out at the default depth of 1.
xpkgindex detects a shallow clone and skips the growth curve, the history line
and the contributor list rather than replaying a truncated log — so the
deployed site has quietly been missing all three. fetch-depth: 0 restores them.
Both now also pass GITHUB_TOKEN, which raises the API rate limit and enables
the author -> login mapping that merges one person's several git identities.
deploy-site's path filter gained .xpkgindex/** and docs/**: the plugin decides
how every package reads, the docs are rendered as site pages, and the cache is
what an offline build renders from. A change to any of them changes the site as
much as a descriptor does, and none of them triggered a deploy.
site-check is new. validate.yml proves the packages compile; this proves they
still render — offline, so a pull request spends no rate limit and the result
depends only on what is in the repository, and --strict, so a replayed history
that disagrees with the tree fails rather than warns. It also fails on any
warning at all, because a warning nobody reads becomes permanent, and asserts
that the pages a reader actually lands on exist in all three locales.