feat(libc): implement the remaining Dinkumware _Atomic helpers

[hypermoist]

What

Implements the 48 Dinkumware _Atomic_* helpers of the system libc.prx that AnyPS5 did not have (it already had _Atomic_fetch_add_4, _Atomic_fetch_sub_4, _Atomic_compare_exchange_weak_4 and _Atomic_load_4), in a new src/DinkumwareAtomics.cpp:

• typed 1/2/4/8-byte _Atomic_store_N, _Atomic_load_N, _Atomic_exchange_N, _Atomic_compare_exchange_{strong,weak}_N, _Atomic_fetch_{add,sub,and,or,xor}_N (the sizes missing upstream)
• _Atomic_is_lock_free_{1,2,4,8}, _Atomic_flag_test_and_set, _Atomic_flag_clear, _Atomic_thread_fence, _Atomic_signal_fence
• the generic _Atomic_copy, _Atomic_exchange, _Atomic_compare_exchange_strong and _Atomic_compare_exchange_weak, which take a byte spinlock flag and a size, lock the flag, memcmp/copy the bytes and unlock, as on the console

Every operation is sequentially consistent whatever memory order it is given, never weaker than the console. The libc.prx bundled with PPSA08427 has observable quirks for unusual orders, which are reproduced: _Atomic_load_8 returns 0 for release, acq_rel or an invalid order, and the 8-byte exchange and fetch operations return 0 without touching memory for an order above memory_order_seq_cst. Recorded in docs/dev/debt/libc.md.

Tested

Linux (CachyOS, GCC Release build, plus a clang -Wall -Wextra syntax check): new guest_dinkumware_atomics test (each family, the order quirks, the flag, the generic functions, and two threads updating a 24-byte object through the locked compare-exchange) passes, as does guest_libc_threads. tools/check_conventions.py passes; tools/pr_overlap.py --branch reports no line overlap.

Differential test against the console: the PPSA08427 libc.prx was mapped into a Linux process and every function here was run side by side with this implementation on random values with every memory order from 0 to 7 (stores only with valid orders, since the console's store falls off its jump table otherwise), and the generic functions on sizes 1 to 40 with equal and unequal expected values; return values, targets, expected buffers and lock flags agree everywhere.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed under Silent stubs in their library's technical debt file
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none
• Unblocks: none
• GPUs tested: n/a
• AI-assisted: yes

🤖 Generated with Claude Code

https://claude.ai/code/session_01Q8tinbP1MUpUaDsbNWnGnu

[github-actions]

Progress report (34454bd → c0cf6e5)

📈 System libraries: 88.86% (+0.15%, +48 implemented functions)

✅ 48 implemented

Library	Name
libc	_Atomic_compare_exchange_strong_1_nid_postfix
libc	_Atomic_compare_exchange_strong_2_nid_postfix
libc	_Atomic_compare_exchange_strong_4_nid_postfix
libc	_Atomic_compare_exchange_strong_8_nid_postfix
libc	_Atomic_compare_exchange_strong_nid_postfix
libc	_Atomic_compare_exchange_weak_1_nid_postfix
libc	_Atomic_compare_exchange_weak_2_nid_postfix
libc	_Atomic_compare_exchange_weak_8_nid_postfix
libc	_Atomic_compare_exchange_weak_nid_postfix
libc	_Atomic_copy_nid_postfix
libc	_Atomic_exchange_1_nid_postfix
libc	_Atomic_exchange_2_nid_postfix
libc	_Atomic_exchange_4_nid_postfix
libc	_Atomic_exchange_8_nid_postfix
libc	_Atomic_exchange_nid_postfix
libc	_Atomic_fetch_add_1_nid_postfix
libc	_Atomic_fetch_add_2_nid_postfix
libc	_Atomic_fetch_add_8_nid_postfix
libc	_Atomic_fetch_and_1_nid_postfix
libc	_Atomic_fetch_and_2_nid_postfix
libc	_Atomic_fetch_and_4_nid_postfix
libc	_Atomic_fetch_and_8_nid_postfix
libc	_Atomic_fetch_or_1_nid_postfix
libc	_Atomic_fetch_or_2_nid_postfix
libc	_Atomic_fetch_or_4_nid_postfix
libc	_Atomic_fetch_or_8_nid_postfix
libc	_Atomic_fetch_sub_1_nid_postfix
libc	_Atomic_fetch_sub_2_nid_postfix
libc	_Atomic_fetch_sub_8_nid_postfix
libc	_Atomic_fetch_xor_1_nid_postfix
libc	_Atomic_fetch_xor_2_nid_postfix
libc	_Atomic_fetch_xor_4_nid_postfix
libc	_Atomic_fetch_xor_8_nid_postfix
libc	_Atomic_flag_clear_nid_postfix
libc	_Atomic_flag_test_and_set_nid_postfix
libc	_Atomic_is_lock_free_1_nid_postfix
libc	_Atomic_is_lock_free_2_nid_postfix
libc	_Atomic_is_lock_free_4_nid_postfix
libc	_Atomic_is_lock_free_8_nid_postfix
libc	_Atomic_load_1_nid_postfix
libc	_Atomic_load_2_nid_postfix
libc	_Atomic_load_8_nid_postfix
libc	_Atomic_signal_fence_nid_postfix
libc	_Atomic_store_1_nid_postfix
libc	_Atomic_store_2_nid_postfix
libc	_Atomic_store_4_nid_postfix
libc	_Atomic_store_8_nid_postfix
libc	_Atomic_thread_fence_nid_postfix

⚪ 5 behaviourally empty (constant return or throw)

Library	Name
libc	_Atomic_is_lock_free_1_nid_postfix
libc	_Atomic_is_lock_free_2_nid_postfix
libc	_Atomic_is_lock_free_4_nid_postfix
libc	_Atomic_is_lock_free_8_nid_postfix
libc	_Atomic_signal_fence_nid_postfix

[github-actions]

Some comparisons could not be completed because a pull request conflicts with the base branch. Review these shared files manually before concluding that there is no overlap.

Pull request	Shared files not compared
PR 3965	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 3987	docs/dev/debt/libc.md
PR 4627	core/libs/prx/libc/CMakeLists.txt
PR 5021	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 5303	docs/dev/debt/libc.md
PR 6044	core/libs/prx/libc/CMakeLists.txt
PR 6079	core/libs/prx/libc/CMakeLists.txt
PR 6084	core/libs/prx/libc/CMakeLists.txt
PR 6085	core/libs/prx/libc/CMakeLists.txt
PR 6086	core/libs/prx/libc/CMakeLists.txt
PR 6144	docs/dev/debt/libc.md
PR 6226	docs/dev/debt/libc.md
PR 6469	docs/dev/debt/libc.md
PR 6541	docs/dev/debt/libc.md
PR 6565	docs/dev/debt/libc.md
PR 6610	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 6686	docs/dev/debt/libc.md
PR 6707	docs/dev/debt/libc.md
PR 6713	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 6819	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 6842	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 6851	core/libs/prx/libc/CMakeLists.txt
PR 6916	docs/dev/debt/libc.md
PR 6975	docs/dev/debt/libc.md
PR 6985	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 7039	docs/dev/debt/libc.md
PR 7081	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 7084	core/libs/prx/libc/CMakeLists.txt
PR 7201	core/libs/prx/libc/CMakeLists.txt
PR 7332	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 7386	docs/dev/debt/libc.md
PR 7411	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 7417	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 7447	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 7470	core/libs/prx/libc/CMakeLists.txt
PR 7473	docs/dev/debt/libc.md
PR 7506	docs/dev/debt/libc.md
PR 7525	core/libs/prx/libc/CMakeLists.txt docs/dev/debt/libc.md
PR 7529	docs/dev/debt/libc.md
PR 7544	docs/dev/debt/libc.md
PR 7545	docs/dev/debt/libc.md
PR 7546	docs/dev/debt/libc.md
PR 7634	docs/dev/debt/libc.md
PR 7648	docs/dev/debt/libc.md