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To: Alan Somers <asomers@freebsd.org>
cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>
Subject: Re: buf(9) woes: when does bcopy do nothing at all?
In-reply-to: <CAOtMX2gdw+eQQU_-DC+EgimbCyw6ynbX1haGLUmn1dApk4rMZw@mail.gmail.com>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
References: <CAOtMX2gdw+eQQU_-DC+EgimbCyw6ynbX1haGLUmn1dApk4rMZw@mail.gmail.com>
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Date: Fri, 26 Apr 2019 08:32:55 +0000
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--------
In message <CAOtMX2gdw+eQQU_-DC+EgimbCyw6ynbX1haGLUmn1dApk4rMZw@mail.gmail=
.com>, Alan Somers writes:

>How is it possible that bcopy() doesn't affect its output array at all?

That conclusion does not follow from your example:

>bcopy(cp, iov->iov_base, cnt);
>r =3D memcmp(cp, iov->iov_base, cnt);
>if (r)
>    printf("uiomove: miscompare\n");

If [cp:cp+cnt] and [iov_base:iov_base+cnt] overlap the bcopy result
is undefined.

Try memmove instead ?

-- =

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    =

Never attribute to malice what can adequately be explained by incompetence=
.