vms-83e8: classic GD/LD TLS relaxation — drop dead __tls_get_addr GOT slot + standing guard

[baron-3dl]

What / why

Investigating the reported residual __tls_get_addr SIGSEGV in C++ OVMX images (vms-83e8, epic vms-da0 F2b).

Ground-truth finding: at base work/vms-ad70-decc-delta @ 39dadb0, the classic GD/LD → Local-Exec relaxation (vms-76a: 16cf1f5 + 1f733a7) is complete. Linking the real cpptest.o against the whole upstream libstdc++/libsupc++/libgcc archives (525 objects) yields 1772 mov %fs:0 LE landings and ZERO surviving classic TLS sequences — no data16 GD lea/call, no direct GD call, no symbolic/deferred __tls_get_addr. The un-relaxed-lea-crashes-in-__tls_get_addr bug does not reproduce here; it was fixed by the two vms-76a commits already in the base. Both hypothesized residual forms (GD data16-indirect from libgcc bid*.o, LD-indirect from libsupc++ eh_globals.o) are handled.

The one real gap found + fixed

The classic GD/LD __tls_get_addr call, under -fno-plt (how Alpine's libstdc++/libgcc are built), reaches its target via an R_X86_64_GOTPCRELX cell. patch_tls_le relaxes the call away, so that cell is dead — but the GOT-collection pass still collected a slot for it, and GOT-fill then died GOT symbol undefined (__tls_get_addr is defined nowhere in a static image). So a clean classic-GD/LD link needed --allow-undefined purely to defer one dead slot. The import loop (vms-e65) and datum loop (vms-76a) already guard __tls_get_addr; the GOT-collection pass was the one place missing it. Added the matching guard (one continue).

Effect on the real cpptest link: GOT 2047→2046, deferred externals 184→183, otherwise byte-identical.

New standing guard

src/vmslink/test/run_test_x86_64_classic_tls.sh — the classic-dialect sibling of run_test_x86_64_tls.sh (which only covers gnu2 TLSDESC and never emits a TLSGD/TLSLD/__tls_get_addr, so the classic path had no end-to-end coverage). Compiles a freestanding program with a cross-TU __thread (GD, data16 lea + -fno-plt indirect call) and a function-local static _Thread_local pair (LD, TLSLD + DTPOFF32) — the exact shapes of bid*.o / eh_globals.o — links with no --allow-undefined, asserts at byte level that no classic GD/LD sequence survives, then activates through the real x86_64 IMGACT.EXE and proves both variables read/write correctly (exit 110). Wired into the vmslink-x86_64 CI job.

Verified

• New classic-TLS test: PASS (host x86_64, real activation).
• gnu2 TLSDESC test (run_test_x86_64_tls.sh): PASS (no regression).
• Base x86_64 additive-gate test (run_test_x86_64.sh): PASS.
• AS.EXE no-regression (run_as_native.sh): running.

x86_64-only instruction rewriting; offset math unchanged (Alpha/VAX untouched, per the conductor's gate).

Routes to the conductor's batched post-0.5 gate.

🤖 Generated with Claude Code