Bug 283698
| Summary: | New version of swab(3) breaks port graphics/dcraw | ||
|---|---|---|---|
| Product: | Base System | Reporter: | Nathan Whitehorn <nwhitehorn> |
| Component: | misc | Assignee: | Warner Losh <imp> |
| Status: | Closed FIXED | ||
| Severity: | Affects Some People | CC: | markj |
| Priority: | --- | Flags: | markj:
mfc-stable14-
markj: mfc-stable13- |
| Version: | 15.0-CURRENT | ||
| Hardware: | Any | ||
| OS: | Any | ||
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Description
Nathan Whitehorn
2024-12-28 20:19:13 UTC
^Triage: over to committer of change in question. It would be easy enough to use the old step method. But the code that calls it so would fail on musl. Ans swab(p,p) relies on the compiler not doing stupid stuff it may have a license to do given the restrict keyword... (In reply to Warner Losh from comment #2) Yeah, exactly -- I'm not sure what the best path is. I found similar reports of problems with MUSL's implementation (e.g. https://www.openwall.com/lists/musl/2022/12/28/1 and someone complaining on Reddit about a MUSL Gentoo system + rawtherapee, which is also affected, that might be the same issue), and MUSL decided not to change their implementation. I think the number of people doing GUI photography on MUSL might be even lower than the number of people doing it on FreeBSD, though. While POSIX does say "If copying takes place between objects that overlap, the behavior is undefined." in the description of swab, it's easy enough to make overlapping objects work. I think I'll post a diff to make that happen, though it will make things slightly more complicated. I doubt there will be any speed difference. We also have a x86 .S version that handles overlap as expected... A commit in branch main references this bug: URL: https://cgit.FreeBSD.org/src/commit/?id=02ebbc781f082df9714e74775700d8c08bac7850 commit 02ebbc781f082df9714e74775700d8c08bac7850 Author: Warner Losh <imp@FreeBSD.org> AuthorDate: 2025-01-06 23:44:21 +0000 Commit: Warner Losh <imp@FreeBSD.org> CommitDate: 2025-01-06 23:46:05 +0000 swab: Fix implementation to support overlapping copies A number of image processing packages assume that swab() can handle to and from being the same. However, POSIX.1 states that overlapping buffers produces undefined results. Our old implementation would produce coherent results, but the recent change to the musl-inspired code does not. Since there's complaints in the forums for these image processing packages for musl and now FreeBSD, update the algorithm to just read a word at a time and bswap16 the results. All FreeBSD's architecutres support unaligned access in userland, and swab is not used in the kernel (g_part_apm has its own copy), so opt for even simpler code that's easier to understand. This makes the overlapping behavior match i386 again, since its assembler routine for swab handles overlapping correctly. PR: 283698 Sponsored by: Netflix Reviewed by: nwhitehorn Differential Revision: https://reviews.freebsd.org/D48259 lib/libc/string/swab.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) It looks like the bug never appeared in stable/14, so there's nothing left to do here. |