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Fix GH-22158: JIT observer dispatch through wrong run_time_cache slot#22258

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Fix GH-22158: JIT observer dispatch through wrong run_time_cache slot#22258
iliaal wants to merge 1 commit into
php:PHP-8.4from
iliaal:fix/gh-22158-jit-observer-phi

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@iliaal iliaal commented Jun 8, 2026

Megamorphic observer dispatch in the tracing JIT read the wrong run_time_cache slot: the ir_PHI_2 operands were reversed against the ir_MERGE_WITH predecessor order, so a user function picked up the internal_function_extension slot. With op_array_extension != internal_function_extension (some extension reserves an op_array handle before the observer registers, e.g. an APM extension) that slot holds 0 and the JIT calls a NULL begin handler. The regression test adds a default-off zend_test.observer.reserve_op_array_handle to force the mismatch in-tree.

Fixes #22158

For a megamorphic call the tracing JIT built the observer handler pointer
with the ir_PHI_2 operands reversed relative to the ir_MERGE_WITH
predecessor order, so a user function read the internal_function_extension
slot instead of op_array_extension. When an extension reserves an op_array
handle before the observer registers the two indices differ, that slot
holds 0, and the JIT calls a NULL begin handler.

The default-off zend_test.observer.reserve_op_array_handle INI forces that
index mismatch so the regression test can reproduce the crash.

Fixes phpGH-22158
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Tracing JIT can dispatch the observer "begin" handler through the wrong run_time_cache slot (NULL deref) on megamorphic calls

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