alpha-crtl: 3 rungs so REAL zlib 1.3.1 links zero-deferred out-of-box

[baron-3dl]

The 3 CRTL rungs

A prior probe measured that all 15 zlib 1.3.1 TUs already compile clean on the alpha-dec-vms port (0 EVAX cc1 defect at harness flags). These three fixes close the remaining LINK / header-surface residuals so REAL zlib compiles and links zero-deferred out-of-box — no labelled probes, no manual symbol adds.

#	Rung	Fix (file:line)
1	zconf.h fires #ifdef VMS #include <unixio.h> (port predefines VMS — correct, it IS a VMS toolchain) but the musl-alpha CRTL header surface had no <unixio.h>	NEW tools/cross-alpha-vms/musl-arch/arch/alpha-dec-vms/unixio.h — faithful DECLARE-ONLY DEC C UNIX-I/O header (open/close/read/write/lseek/dup/dup2/isatty/unlink/access/ftruncate/fsync/chdir/getcwd), every entry already implemented by the port musl; VMS-target-scoped in the arch overlay
2	errno accessor UNDEF at LINK — musl's errno = (*__errno_location()), an undecorated musl-internal name the alpha cc1 does not map to decc$*, so the linker-view decc$ enumeration misses it	src/vmslink/mk_decc_shr.sh — add ___errno_location=PROCEDURE to the alpha-branch symbol vector (LINK.EXE's EVAX reader represents the external C symbol __errno_location with one leading underscore prepended, uniformly for def + ref → ___errno_location, three underscores, the exact name gzread.obj deferred). Brings alpha to parity with the generic branch, which already exports the errno accessor
3	OTS$DIV_UL/OTS$REM_UI UNDEF — the port lowers integer divide/rem to OTS$ calls; those live in the SEPARATE LIBOTS$ shareable, which DECC$SHR imports but does not re-export	tools/cross-alpha-vms/joint-e2e/build-joint-image.sh — add --use LIBOTS$SHR.EXE alongside --use DECC$SHR.EXE in the canonical consumer link recipe. LINK binds only referenced imports → inert for OTS-free programs

errno-mechanism note

The C symbol is __errno_location (two underscores; how GNU nm reports it in libc.a). LINK.EXE's EVAX symbol reader prepends one leading underscore to external C symbols — uniformly for the musl definition and every consumer reference — so at the link/vector level the name is ___errno_location (three underscores). This is why the two-underscore C-form export did NOT resolve gzread.obj's reference (%LINK-F-UNDEF, EVAX: undefined symbol '___errno_location' referenced by gzread.obj); exporting the three-underscore name closes it. The DEC-C-decorated decc$get_errno_addr is a different (DEC C) errno ABI and is unrelated to what musl-compiled consumer code references.

Zlib zero-deferred out-of-box — proof

Containerized (ovmx-cross-alpha-vms), build-to-/tmp, Rule-9-clean. Not run under qemu-user (BOOT-A/B is the runtime test).

• REAL zlib 1.3.1, pinned sha256 9a93b2b7dfdac77ceba5a558a580e74667dd6fede4585b91eefb60f03b72df23.
• All 15 TUs + a compress/uncompress round-trip main cross-compiled at harness flags (-mpointer-size=64 -g0) + -DZ_HAVE_UNISTD_H → compile clean.
• Linked against the FIXED DECC$SHR + LIBOTS$ via the FIXED recipe (--transfer __main --use DECC$SHR.EXE --use LIBOTS_SHR.EXE):
  • zlib link rc=0 ; LINK-F-UNDEF count=0 → ZERO-DEFERRED OUT-OF-BOX (no manual adds)
  • image is Machine: Alpha, Type: DYN
• Rung 1 proven live: unixio.h present at .../arch/alpha-dec-vms/unixio.h; all 15 TUs (incl. gzread, which pulls <unixio.h> via zconf.h) compile.

No regression

• joint_e2e default (crt0 + joint_main, --use DECC$SHR.EXE only) rebuilt live → links clean (rung-3's LIBOTS is inert for OTS-free programs).
• crtl_rms (aarch64 run_vmsrms_native.sh, which already exports __errno_location): depends solely on the generic branch of mk_decc_shr.sh; the errno edit is inside the alpha branch (if [ "$OVMX_DECC_ARCH" = alpha ]), so that branch is byte-unchanged → structurally cannot regress. unixio.h is alpha-arch-scoped; the LIBOTS edit is joint-only.

zlib build recipe (for the PR record)

# harness flags == build-joint-image.sh cc1 flags; -DZ_HAVE_UNISTD_H is what
# zlib's own ./configure sets (makes zconf.h include <unistd.h> then, under the
# port-predefined VMS, <unixio.h>). Include path = the alpha musl surface.
ALPHA_MUSL_INC="-I$MUSL_SRC/arch/alpha-dec-vms -I$MUSL_SRC/arch/generic \
  -I$MUSL_SRC/obj/src/internal -I$MUSL_SRC/src/include -I$MUSL_SRC/src/internal \
  -I$MUSL_SRC/obj/include -I$MUSL_SRC/include"
ZCF="-mpointer-size=64 -g0 -DZ_HAVE_UNISTD_H $ALPHA_MUSL_INC -I<zlib-src>"
for c in adler32 compress crc32 deflate gzclose gzlib gzread gzwrite \
         infback inffast inflate inftrees trees uncompr zutil; do
    alpha-dec-vms-gcc $ZCF -c $c.c -o $c.obj
done
LINK.EXE --transfer __main --use DECC\$SHR.EXE --use LIBOTS_SHR.EXE -o zlib_e2e.exe *.obj

Out-of-scope observation (separate, not a CRTL rung)

Compiling zlib at -O2 (not harness flags) surfaces an EVAX cc1/as codegen defect: deflate.c at -O2 produces .s the alpha-dec-vms as rejects (Error: syntax error). Independent of these three rungs (they are all LINK / header-surface); tracked separately.

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