llvm_jit: DLLExport storage on jit_table_at globals (#2802 cache-hit fix)

[borisbat]

Fixes the Windows JIT DLL cache crash documented at #2802. Follow-up to #2808 (now merged) — that added the -jit-no-cache opt-out flag, this is the actual cache-side fix so the flag stays a "skip the cache entirely" convenience rather than a workaround for broken behavior.

What was broken

The cached .jitted_scripts/<ns>/<hash>.dll bakes runtime function-pointer addresses into a few global initializers at codegen, then ResolveExternVisitor walks the AST after every DLL load and overwrites each slot via set_glob_address with the current-session address — that handoff is what keeps cache-hit reloads safe across ASLR shifts.

add_table_linkage on the jit_table_at/find/erase globals only set LLVMExternalLinkage, no DLLExport storage class. On Windows that leaves the symbol out of the DLL export table, so set_glob_address (GetProcAddress + write-through-pointer) finds nothing and silently returns false. The codegen-time address — valid in the session that wrote the DLL — survives unchanged into every subsequent session, where ASLR has placed the runtime DLL somewhere else. The JIT'd code loads the stale pointer and crashes inside the first table operation.

dumpbin /exports on a pre-fix cached DLL confirms `jit`table_at`tString` glob is missing while save_address_global's builtin function-pointer globals (which use set_public_linkage → DLLExport) are present.

Fix

• add_table_linkage mirrors set_public_linkage's DLLExport linkage + DLLExportStorageClass combo. Post-fix dumpbin /exports shows jit_table_at_* in the exports table.
• LLVM_JIT_CODEGEN_VERSION bumped 0x09 → 0x0a so previously-written cached DLLs miss on first run after this lands and get GC'd.

Test

tests/jit_tests/dll_cache.das probe now exercises table[k] (was x + 1) so jit_table_at_tString lands in the emitted globals, exercising the codegen + fixup path the fix targets. The cache-behavior assertions are unchanged.

Verification on Windows

• Two sessions of daslang -jit dasProfile/tests/dict.das -- --nomain (the original Windows JIT DLL cache: stale absolute-address bake survives across runs → AV on cache hit #2802 crash repro), cache cleared before session 1, both exit 0 with "dictionary", 0.013941000, 10.
• Full jit_tests/ suite under -jit: 229 passed, 8 pre-existing missing prerequisite 'UnitTest' failures (build infra, unrelated).
• Lint: 0 issues on the 4 changed files.
• Format: all 4 files already formatted.

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com

[Copilot]

Pull request overview

This PR fixes a Windows-specific crash on JIT DLL cache hits by ensuring JIT-emitted table helper globals are exported from cached DLLs (so their baked addresses can be patched on reload), and by making missing exports fail loudly instead of silently producing stale pointers.

Changes:

• Export jit_table_at/find/erase globals from JIT DLLs on Windows by applying DLLExport linkage + storage class.
• Make DLLHandle.set_glob_address panic with a precise diagnostic when a required exported global symbol is missing.
• Bump LLVM_JIT_CODEGEN_VERSION to invalidate previously cached DLLs, and update the DLL cache test probe to exercise table[k] so the relevant globals are emitted.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/jit_tests/dll_cache.das	Updates the probe program to use table["a"] so jit_table_at_* globals are emitted and the regression is caught by the new panic.
modules/dasLLVM/daslib/llvm_macro.das	Bumps the JIT codegen version to force cache miss/GC of old cached DLLs.
modules/dasLLVM/daslib/llvm_jit_common.das	Ensures JIT table helper globals are marked for DLL export (linkage + storage class).
modules/dasLLVM/daslib/llvm_dll_utils.das	Converts silent “missing export” behavior into a hard failure with a targeted panic message.

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