Fix #635: Segfault in async result via dangling pointer from optimized for loop#671
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…m optimized for loop Two bugs combined to cause the crash: 1. The optimized for loop (chaiscript_optimizer.hpp) stored the loop counter as a stack-local `int` and exposed it to ChaiScript via `var(&i)`, creating a reference-type Boxed_Value pointing to the stack frame. 2. The `:=` operator's `Data::operator=` performed a shallow clone of the Any (copying the reference_wrapper, not the value), so `ret := i` made `ret` alias the stack-local `int`. When the optimized loop's frame unwound, `ret` held a dangling pointer. Fix 1: The optimizer now heap-allocates the loop counter via `Boxed_Value(start_int)` and obtains a reference to the heap-allocated int for the native C++ loop. The Boxed_Value's shared_ptr ensures the storage outlives any copies. Fix 2: The `:=` operator now deep-copies arithmetic values via `Boxed_Number::clone` instead of the shallow `assign()`, ensuring value semantics. This also fixes a pre-existing aliasing bug where `a := b; ++b` would incorrectly mutate `a`. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
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@leftibot this will always fail when compiled without thread support - make sure this file is excluded from testing in those cases.
… thread support Requested by @lefticus in PR ChaiScript#671 review. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
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Addressed review feedback from @lefticus. New commits: |
| // Verify that := performs a value copy, not an alias | ||
| var a = 10 | ||
| var b = 20 | ||
| a := b |
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@leftibot is it an accident / mistake that := works on already created objects at all? Is it intended only for variable declarations?
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Looking at the codebase, Evidence it's by design:
The semantic distinction appears to be:
This is actually what makes the prelude's range wrapper work — the That said, this raises a concern about this PR's change. The PR adds deep-copy for arithmetic types in Would you prefer to keep |
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@leftibot yeah, remove your change for |
…antics Reverts the arithmetic deep-copy added to := in chaiscript_eval.hpp, restoring its original reference-assign behavior as requested. The optimizer fix (heap-allocated loop counter) remains and is sufficient to prevent the ChaiScript#635 segfault. Updated tests to use correct expected values for reference-assign semantics and added more thorough coverage: nested loops, multiple async calls, and value-assign comparison. Requested by @lefticus in PR ChaiScript#671 review. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
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Addressed review feedback from @lefticus. New commits: |
Summary
intexposed viavar(&i). When:=copied this reference-typeBoxed_Value, the returned value held a dangling pointer after the loop frame unwound. Now heap-allocates the counter viaBoxed_Value(start_int).:=operator fix:Data::operator=performed a shallow clone (copying thereference_wrapperorshared_ptr, not the value), soret := ialiased the same storage. Now deep-copies arithmetic values viaBoxed_Number::clone, giving correct value semantics.assign_no_aliasing.chaiandasync_return_value.chaicovering both the aliasing fix and the async crash.Root cause
The
For_Loopoptimizer inchaiscript_optimizer.hppcreated a native C++int ion the stack and registered it as a ChaiScript variable withvar(&i)(a reference-typeBoxed_Value). When the loop body executedret := i,Boxed_Value::assign()→Data::operator=cloned theAny(copying thereference_wrapper<int>— still pointing to the stack local) and copied the rawm_data_ptr/m_const_data_ptrfrom the rhs. After the optimizer lambda returned, the stack-localintwas destroyed, leavingretwith a dangling pointer that crashed inBoxed_Number::get_as<int>().Test plan
49999 49999(was garbage/crash):=aliasing fix verified:a := b; ++b→a=20, b=21(wasa=21, b=21)🤖 Generated with Claude Code