[Bug 291720] [REGRESSION] 66eb78377bf1 causes environment corruption on some machines

From: <bugzilla-noreply_at_freebsd.org>
Date: Tue, 16 Dec 2025 18:40:39 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=291720

Robert Clausecker <fuz@FreeBSD.org> changed:

           What    |Removed                     |Added
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           Assignee|bugs@FreeBSD.org            |fuz@FreeBSD.org

--- Comment #8 from Robert Clausecker <fuz@FreeBSD.org> ---
The problem is probably that machines without TZCNT resp. BMI1 behave
differently on one of the tzcnt instruction.  This was previously fine, but I
think the change has triggered the relevant edge case.

As a stop gap solution, could someone please comment out the line

ARCHFUNC(__stpncpy, baseline)

in lib/libc/amd64/string/stpncpy.S?  I don't have the environment to commit
right now, removing or commenting out this line effectively disables the
affected code.

I will investigate this shortly.

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