Mathieu Benoit
a42e43bcf1
Built at stage 1, failed at stage 2, in gold:
<artificial>:(.text+0xc44e): undefined reference to
`void gold::gold_error_at_location<32, true>(...)'
`<artificial>` and the .ltrans object names are LTO's, and it does not come from
makepkg -- the chroot carries !lto with an empty LTOFLAGS. It comes from the
PKGBUILD: --enable-pgo-build=lto. gold's explicitly-instantiated templates do
not survive it here. Stage 1 got away with it because the host's GCC did the
work; stage 2 uses ours, at -O2 -march=z13 where stage 1 passed no flags.
PGO and LTO are build-time optimisations: what changes is how long binutils
takes to compile and how fast the linker runs, not what it can do. The
alternatives were removing gold, a linker Arch ships, or debugging LTO template
instantiation in a linker upstream has deprecated.
The first attempt at this hook looked for --with-build-config=bootstrap-lto,
which is in gcc's PKGBUILD, not binutils'. Its own assertion caught it.
--- FR ---
Bâti à l'étage 1, échoué à l'étage 2, dans gold :
<artificial>:(.text+0xc44e): undefined reference to
`void gold::gold_error_at_location<32, true>(...)'
`<artificial>` et les noms d'objets .ltrans sont ceux du LTO, et il ne vient pas
de makepkg — le chroot porte !lto avec un LTOFLAGS vide. Il vient du PKGBUILD :
--enable-pgo-build=lto. Les gabarits explicitement instanciés de gold n'y
survivent pas. L'étage 1 s'en tirait car le GCC de l'hôte faisait le travail ;
l'étage 2 utilise le nôtre, à -O2 -march=z13 là où l'étage 1 ne passait rien.
PGO et LTO sont des optimisations de construction : ce qui change, c'est la durée
de compilation et la vitesse du lieur, pas ce qu'il sait faire. Les options
étaient de retirer gold, un lieur qu'Arch livre, ou de déboguer une instanciation
de gabarit sous LTO dans un lieur abandonné en amont.
La première version de ce hook cherchait --with-build-config=bootstrap-lto, qui
est dans le PKGBUILD de gcc, pas de binutils. Sa propre assertion l'a arrêtée.
Assisted-by: Claude Opus 5
88 lines
4.6 KiB
Bash
Executable file
88 lines
4.6 KiB
Bash
Executable file
#!/usr/bin/env bash
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# binutils: install into /usr/lib, not /usr/lib64.
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#
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# THIS IS THE ROOT OF A CHAIN, and the chain is worth writing down because
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# nothing in it looks related to anything else in it:
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#
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# 1. On s390x, GCC's and binutils' default MULTILIB_OSDIRNAME is lib64, so
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# binutils installs libiberty.a into /usr/lib64 -- creating that directory
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# as a REAL directory. On Arch, /usr/lib64 is a SYMLINK to lib.
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# 2. meson chooses its default libdir by looking at the system: 64-bit plus a
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# real /usr/lib64 means "lib64". A symlink does not count, which is why
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# Arch never sees this and arch-meson passes no --libdir at all.
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# 3. pkgconf is a meson package, so it installed into /usr/lib64 -- and
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# COMPILED IN its search path as /usr/lib64/pkgconfig.
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# 4. Every .pc file in the distribution is in /usr/lib/pkgconfig. So every
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# pkg-config lookup inside the chroot failed. libxslt reported it as
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#
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# configure: error: Package requirements (python-3.14) were not met:
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# Package 'python-3.14' not found
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#
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# with python 3.14.7 installed and /usr/lib/pkgconfig/python-3.14.pc
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# sitting right there.
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#
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# Step 4 reads as a missing dependency. Step 1 is a linker library nobody
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# thinks about. Fixing only the visible end -- pkgconf's search path -- would
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# leave the real /usr/lib64 there, and the next meson package would land in it.
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#
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# --libdir is set explicitly rather than left to the target default, which is
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# what Arch's layout means: one library directory, /usr/lib, with lib64 as a
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# compatibility symlink.
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set -euo pipefail
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python3 - <<'ZZPY'
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import io, re
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lines = io.open("PKGBUILD", encoding="utf-8").read().split("\n")
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hit = [i for i, l in enumerate(lines) if re.search(r"/configure\b", l) and "#" not in l.split("/configure")[0]]
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assert len(hit) == 1, "binutils: expected one configure call, got %d" % len(hit)
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i = hit[0]
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indent = re.match(r"^[ \t]*", lines[i]).group(0)
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assert lines[i].rstrip().endswith("\\"), "binutils: configure does not continue"
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lines.insert(i + 1, indent + " --libdir=/usr/lib \\")
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io.open("PKGBUILD", "w", encoding="utf-8").write("\n".join(lines))
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ZZPY
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grep -A1 -E "/configure( |\\\\)" PKGBUILD | grep -q -- '--libdir=/usr/lib' || {
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echo "binutils: --libdir is not on the configure line" >&2; exit 1; }
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echo "binutils: libdir pinned to /usr/lib (keeps /usr/lib64 a symlink)"
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# --- no PGO+LTO build ---------------------------------------------------------
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#
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# binutils built at stage 1 and failed at stage 2, in gold:
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#
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# <artificial>:(.text+0xc44e): undefined reference to
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# `void gold::gold_error_at_location<32, true>(...)'
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# collect2: error: ld returned 1 exit status
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#
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# `<artificial>` and the .ltrans object names are LTO's. It does not come from
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# makepkg -- the chroot's OPTIONS carry !lto and LTOFLAGS is empty. It comes
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# from the PKGBUILD itself: --enable-pgo-build=lto, a profile-guided build with
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# link-time optimisation, which passes -flto=jobserver. gold's
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# explicitly-instantiated templates do not survive it here.
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#
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# Stage 1 got away with it because the host's GCC did the work. Stage 2 uses
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# ours, on s390x, at -O2 -march=z13 where stage 1 passed no flags at all.
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#
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# PGO and LTO are BUILD-TIME optimisations: dropping them changes how long
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# binutils takes to compile and how fast the resulting linker runs, not what it
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# can do. The alternatives were disabling gold -- removing a linker Arch ships
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# -- or debugging an LTO template instantiation bug in a linker upstream has
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# deprecated. For a bootstrap, a binutils that works beats a binutils that is
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# five percent faster; PGO also roughly triples the build, which this port pays
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# for on every stage.
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python3 - <<'ZZPY'
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import io, re
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lines = io.open("PKGBUILD", encoding="utf-8").read().split("\n")
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hit = [i for i, l in enumerate(lines) if "--enable-pgo-build" in l]
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assert len(hit) == 1, "binutils: expected one --enable-pgo-build line, got %d" % len(hit)
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i = hit[0]
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assert lines[i].strip().startswith("--enable-pgo-build"), \
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"binutils: --enable-pgo-build shares its line: %r" % lines[i]
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ind = re.match(r"^[ \t]*", lines[i]).group(0)
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lines[i] = ind + "# --enable-pgo-build=lto removed: gold's templates do not survive"
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lines.insert(i + 1, ind + "# LTO here, and PGO is build-time only -- no feature is lost.")
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io.open("PKGBUILD", "w", encoding="utf-8").write("\n".join(lines))
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ZZPY
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grep -q "enable-pgo-build=lto removed" PKGBUILD || {
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echo "binutils: the PGO line was not commented" >&2; exit 1; }
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grep -qE "^[[:space:]]*--enable-pgo-build" PKGBUILD && {
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echo "binutils: an active --enable-pgo-build line survived" >&2; exit 1; }
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echo "binutils: PGO+LTO build dropped"
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