#21 call asan on setjmp

[balupillai]

Note

Low Risk
Low risk: behavior changes only under __SANITIZE_ADDRESS__, but it touches the core longjmp-based error/exception path during ASAN-instrumented builds.

Overview
When compiling with AddressSanitizer (__SANITIZE_ADDRESS__), thrlua.h now maps lua_do_setjmp/lua_do_longjmp to the system setjmp/longjmp instead of the custom assembly implementations.

This lets ASAN intercept the jump functions and correctly unpoison skipped stack frames, reducing ASAN false positives during Lua error handling.

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[Copilot]

Pull request overview

This PR updates Lua’s longjmp-based error handling to better cooperate with AddressSanitizer by invoking an ASan “no return” hook before performing longjmp.

Changes:

• Adds a declaration for __asan_handle_no_return.
• Wraps LUAI_THROW (for _longjmp/_setjmp and longjmp/setjmp configurations) to call __asan_handle_no_return() before lua_do_longjmp.

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[balupillai]

DON'T DELETE

[cursor]

ASAN detection misses Clang before version 21

Low Severity

The ASAN check uses only __SANITIZE_ADDRESS__, which GCC has supported since 4.8 but Clang only added in version 21 (2026). Clang versions before 21 use __has_feature(address_sanitizer) instead. Builds with older Clang and -fsanitize=address will silently skip this block and continue using the custom asm setjmp/longjmp, defeating the purpose of the ASAN fix. The common portable pattern checks both: defined(__SANITIZE_ADDRESS__) || (defined(__has_feature) && __has_feature(address_sanitizer)).

 

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

There are 2 total unresolved issues (including 1 from previous review).

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[cursor]

ASAN path incorrectly triggers extern declarations for setjmp

Medium Severity

When __SANITIZE_ADDRESS__ is defined, lua_do_setjmp is #define'd to setjmp before the #ifdef lua_do_setjmp guard on line 239, causing the extern declaration block (designed for custom asm symbols) to be entered. The declarations expand through the platform's setjmp macro — on glibc this happens to produce a valid _setjmp re-declaration, but on platforms where setjmp(env) expands to e.g. sigsetjmp(env, 1), the result is invalid syntax. The ASAN path duplicates the intent of the #else fallback on lines 243–245 but inadvertently goes through the wrong code path.

Additional Locations (1)

• src/thrlua.h#L238-L242

 

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