Date: Fri, 26 Apr 2019 11:41:18 -0700 From: Mark Millard <marklmi@yahoo.com> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: Alan Somers <asomers@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: buf(9) woes: when does bcopy do nothing at all? Message-ID: <6CF6472E-1100-475D-987C-071E916D64E8@yahoo.com> In-Reply-To: <23438.1556267575@critter.freebsd.dk> References: <CAOtMX2gdw%2BeQQU_-DC%2BEgimbCyw6ynbX1haGLUmn1dApk4rMZw@mail.gmail.com> <23438.1556267575@critter.freebsd.dk>
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On 2019-Apr-26, at 01:32, Poul-Henning Kamp <phk@phk.freebsd.dk> wrote:
> --------
> In message =
<CAOtMX2gdw+eQQU_-DC+EgimbCyw6ynbX1haGLUmn1dApk4rMZw@mail.gmail.com>, =
Alan Somers writes:
>=20
>> How is it possible that bcopy() doesn't affect its output array at =
all?
>=20
> That conclusion does not follow from your example:
>=20
>> bcopy(cp, iov->iov_base, cnt);
>> r =3D memcmp(cp, iov->iov_base, cnt);
>> if (r)
>> printf("uiomove: miscompare\n");
>=20
> If [cp:cp+cnt] and [iov_base:iov_base+cnt] overlap the bcopy result
> is undefined.
>=20
> Try memmove instead ?
I only see a bcopy man page bcopy(3) but it says:
DESCRIPTION
The bcopy() function copies len bytes from string src to string =
dst. The
two strings may overlap. If len is zero, no bytes are copied.
Is a kernel bcopy likely to be any different?
=3D=3D=3D
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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