[Windows] Search for closest free page in x64 JIT memory allocation#124
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mazong1123 merged 1 commit intomainfrom Mar 25, 2026
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The old x86_64 Windows implementation of allocate_jit_memory scanned linearly from func_addr - 2GB upward, which often allocated memory ~2GB away from the function. This could land in/near the stack region, disrupting the stack guard page and causing STATUS_STACK_OVERFLOW (0xc00000fd) during parallel test execution. This change replaces the linear scan with a bidirectional closest-first search (matching the existing aarch64 Windows and Unix implementations). The allocator now searches outward from the function address at +offset and -offset, finding the closest available page first. This is an improved version of PR #122 that fixes two additional issues: - Searches both directions (not just downward) for robustness - Avoids an infinite loop when checked_sub fails by keeping offset increment outside the inner direction loop Also adds tests: - Unit test verifying JIT allocation is close to source (<128MB, not ~2GB) - Unit test verifying JIT allocation is not near the stack region - Integration test for stack growth after patching - Integration test for concurrent patching with deep stack usage (8 threads) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Problem
The x86_64 Windows implementation of
allocate_jit_memory_windowsscanned linearly fromfunc_addr - 2GBupward, which often allocated memory ~2GB away from the function. This could land in/near the stack region, disrupting the stack guard page and causingSTATUS_STACK_OVERFLOW(0xc00000fd) during parallel test execution.Observed: Function at
0x7ff65ad71670, JIT at0x7ff5dad80000, distance: 2047 MBFix
Replace the linear scan with a bidirectional closest-first search, matching the existing aarch64 Windows and Unix implementations. The allocator now searches outward from the function address at
+offsetand-offset, finding the closest available page first.This is an improved version of #122 that additionally:
checked_subfails by keepingoffset += page_sizeoutside the inner direction loopTests Added
Unit tests (
src/injector_core/common.rs):test_jit_allocation_is_close_to_source— verifies JIT allocation is within 128MB of the function (fails with old code at 2047MB distance)test_jit_allocation_not_in_stack_region— verifies JIT allocation is >16MB from the stackIntegration tests (
tests/stack_safety.rs):test_stack_growth_works_after_patching— patches a function then does deep recursion (2000 frames)test_concurrent_patching_with_deep_stack_usage— 8 threads concurrently patch + exercise deep recursion (replicates the original crash scenario)