fix: add get_pgcstack_fallback to non-allocating allowlist (aarch64 false positive)#105
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topolarity merged 1 commit intoJun 22, 2026
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`fn_may_allocate` already whitelists `get_pgcstack` and `get_pgcstack_static`
as never-allocating, but omits the `get_pgcstack_fallback` variant that
aarch64 (Apple Silicon) codegen emits to fetch the per-task GC stack pointer.
As a result `classify_runtime_fn("jl_get_pgcstack_fallback")` returns
`(:runtime, true)` and `check_allocs` reports a spurious
`AllocatingRuntimeCall` for allocation-free functions on aarch64.
This mirrors the earlier fix for the `_static` variant (e44be86).
Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
topolarity
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This seems to suggest TLS is not getting setup correctly somehow @ChrisRackauckas-Claude which is probably worthy of further investigation, but this is a good fix regardless
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Summary
fn_may_allocate(src/classify.jl) whitelistsget_pgcstackandget_pgcstack_staticas never-allocating, but omitsget_pgcstack_fallback— the variant aarch64 (Apple Silicon) codegen emits to fetch the per-task GC stack pointer.As a result,
classify_runtime_fn("jl_get_pgcstack_fallback")returns(:runtime, true), andcheck_allocsreports a spuriousAllocatingRuntimeCallfor allocation-free functions on aarch64.This one-liner adds
"get_pgcstack_fallback"to the never-allocates allowlist, right next to"get_pgcstack_static". It mirrors the earlier_staticfix in e44be86.Fixes #104.
Verification
Pkg.test()passes on Julia 1.10 with the patch applied.Context
_staticvariant for exactly the same reason;get_pgcstack_fallbackis a third pgcstack-fetch variant the whitelist missed.