[voidlakhan]

What

Implement timingsafe_bcmp (NID aWl82o9ammc) in libc matching FreeBSD 11.4 behavior, and add test coverage in GuestStrings.cpp.

Reference:
https://github.com/freebsd/freebsd-src/blob/release/11.4.0/lib/libc/string/timingsafe_bcmp.c

Tested

Windows 10, core/libs/tests/GuestStrings.cpp checking equal, non-equal at start/middle/end, reversed order, sub-lengths, empty buffers, and high-bit byte sequences.

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
• Fixes: none
• Unblocks: none
• GPUs tested: n/a
• AI-assisted: yes

[github-actions]

Progress report (26fa121 → c08fe41)

📈 System libraries: 26.23% (+0.0022%, +1 implemented functions)

✅ 1 implemented

Library	Name
libc	timingsafe_bcmp_nid_postfix

Changed libraries (implemented exports)

Library	Before	After	Change
libc	1484/1500 (98.93%)	1485/1501 (98.93%)	+0.0007%

[oneandonlydean]

@voidlakhan thanks, the port reads well: the body matches FreeBSD 11.4's timingsafe_bcmp.c, has no early exit, the NID recomputes, and the new assertions are registered.

One thing before it can go in: the repository owner decided on 28 Oct that code ported from FreeBSD or other permissively licensed sources keeps its original copyright notice and licence text, verbatim. timingsafe_bcmp.c is ISC-licensed (Copyright (c) 2010 Damien Miller). Could you add that notice and the ISC licence text to Strings.cpp? Put it next to the function, or at the top of the file with a line naming the function and the source file and revision it came from.

[rooklz]

I ran a host-side check on macOS arm64 (Apple clang, -fsanitize=address,undefined). The harness holds the function body from 33b5bee and the 11 new Require lines word for word. They all pass, and the NID aWl82o9ammc recomputes from timingsafe_bcmp.

Mutants against the new assertions:

Mutant	Result
loop starts at 1	killed (safeD)
loop stops one byte early	killed
& instead of ^	killed
ret == 0 inverted	killed
p1[i] - p2[i] instead of ^	equivalent (non-zero exactly when the bytes differ)
return ret; (raw OR of the XORs)	survives
return -(ret != 0);	survives

The body follows FreeBSD 11.4, where the function returns (ret != 0), so it gives exactly 1 when the buffers differ. The tests only check != 0, so nothing would catch a change that returns some other non-zero value. If 1 is the intended contract, two lines pin it down and kill both survivors:

     Require(timingsafe_bcmp_nid_postfix(highB, highA, 2) != 0);
+    Require(timingsafe_bcmp_nid_postfix(safeA, safeB, 6) == 1);
+    Require(timingsafe_bcmp_nid_postfix(highA, highB, 2) == 1);

Apart from that, and the licence notice @oneandonlydean asked for, this looks right to me. I did not build guest_strings itself (the macOS lane here has no submodules), and I did not test on a console.

AI-assisted: yes

[github-actions]

Other open pull requests touch the same code. Merging one will break the other, or both implement the same thing. If this one builds on them, list them in Depends on.

Pull request	Conflicting files (lines on main)	Same exports	Same new files
PR 10113	docs/dev/debt/libc.md L270
PR 10226	docs/dev/debt/libc.md L270
PR 10349	docs/dev/debt/libc.md L270
PR 14235	docs/dev/debt/libc.md L270

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 5021	core/libs/prx/libc/src/Strings.cpp docs/dev/debt/libc.md
PR 7081	docs/dev/debt/libc.md
PR 7386	docs/dev/debt/libc.md
PR 7447	docs/dev/debt/libc.md
PR 7715	docs/dev/debt/libc.md
PR 8150	docs/dev/debt/libc.md
PR 8965	core/libs/prx/libc/src/Strings.cpp core/libs/tests/GuestStrings.cpp docs/dev/debt/libc.md
PR 9340	docs/dev/debt/libc.md
PR 9371	docs/dev/debt/libc.md
PR 9447	docs/dev/debt/libc.md
PR 9526	docs/dev/debt/libc.md
PR 9929	docs/dev/debt/libc.md
PR 10405	docs/dev/debt/libc.md
PR 10987	docs/dev/debt/libc.md
PR 11332	docs/dev/debt/libc.md
PR 11625	docs/dev/debt/libc.md
PR 11831	core/libs/prx/libc/include/Api.hpp docs/dev/debt/libc.md
PR 12560	docs/dev/debt/libc.md
PR 14212	docs/dev/debt/libc.md

[voidlakhan]

@oneandonlydean @rooklz Updated:

1. Added the verbatim ISC copyright notice for timingsafe_bcmp (Copyright (c) 2010 Damien Miller) and attribution to FreeBSD 11.4's timingsafe_bcmp.c directly above timingsafe_bcmp_nid_postfix in Strings.cpp. Added the corresponding technical debt entry in docs/dev/debt/libc.md.
2. Added the two suggested exact-return assertions (== 1) in GuestStrings.cpp.
3. Rebased onto current main (10bec5c322). Local convention checks and the guest_strings tests pass.

[voidlakhan]

@adriadam10 The merge conflict has now been resolved. I've rebased PR #12586 onto the latest main, preserved all existing debt entries, and pushed the updated branch.

The focused guest_strings test and convention checks pass locally. The updated Build and Progress report workflows are now running.

Could you please take another look at the updated head when convenient? Thanks!

[voidlakhan]

Investigated the macOS write-watch CI failure.

This failure is unrelated to the timingsafe_bcmp changes in this PR.

The failure was caused by duplicate CTest registrations in core/libs/tests/write_watch/CMakeLists.txt for:

• write_watch_execute-fault
• write_watch_read-fault

The duplicate registrations caused CMake configuration to fail before the build or tests could run.

This was a pre-existing issue on the base branch and was addressed separately in PR #13220 (test(libc): register the macOS write watch fault tests once).

No changes to the timingsafe_bcmp implementation are needed to address this failure.