Date: Tue, 11 Apr 2017 20:57:16 -0700 From: "Christopher R. Bowman" <crb@chrisbowman.com> To: Fabian Keil <freebsd-listen@fabiankeil.de> Cc: freebsd-hackers@freebsd.org Subject: Re: Dtrace oddity Message-ID: <15DF9D2C-40A4-4341-AE7E-E8A776ED3F09@ChrisBowman.com> In-Reply-To: <20170411151426.3b760182@fabiankeil.de> References: <CD5E9B03-6147-4E4D-BED6-6C45022051E3@chrisbowman.com> <20170411151426.3b760182@fabiankeil.de>
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Fabian,
That was hugely helpful. I should have known about the extra =
mmap sys calls, but sometimes your mind only sees what it expects to =
see. Checking for negative values on open is also the right thing to do =
(I had mis-read the man page to imply that zero indicated a failure to =
open). But the real help was putting one of the flags for mmap. I =
don=E2=80=99t think FreeBSD used to check for that as I have a vague =
recollection that this code used to work on a pervious version.
Thanks SO SO much for the help!
Christopher
--------
Christopher R. Bowman
email: crb@ChrisBowman.com
World Wide GSM cell: +1 (408) 476-2299
> On Apr 11, 2017, at 6:14 AM, Fabian Keil =
<freebsd-listen@fabiankeil.de> wrote:
>=20
> Christopher Bowman <crb@chrisbowman.com> wrote:
>=20
>> The man page lists a bunch of reasons for EINVAL so I want to
>> investigate this and I don=E2=80=99t quite know good strategies to =
debug the
>> kernel (yet) so I thought I=E2=80=99d experiment with Dtrace a bit. =
Here is the
>> oddity: when I run Dtrace and then run my test program I get the
>> following output from Dtrace:
>>=20
>> crb@retread:60> dtrace -n 'syscall:freebsd:mmap:entry /execname =3D=3D =
"test"/ {}'
>> dtrace: description 'syscall:freebsd:mmap:entry ' matched 1
>> probe CPU ID FUNCTION:NAME
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>> 0 63401 mmap:entry=20
>>=20
>> I think Dtrace is indicating that the mmap syscall was called 12 =
times
>> by my test program yet I can see how the program below would have =
done
>> that.
>=20
> A bunch of mmap syscalls occur before main is even entered.
> Try running your program with truss to see what's going on.
>=20
>> Here is my program:
> [...]
>> printf("opening device %s\n", argv[1]);
>> int device =3D open (argv[1], O_RDWR);
>> if (device =3D=3D 0) {
>=20
> You should check for -1 here.
>=20
>> void *pa =3D mmap (0, 4095, PROT_READ | PROT_WRITE, 0, device, =
0);
>=20
> No flags? =46rom the mmap man page:
>=20
> | [EINVAL] None of MAP_ANON, MAP_PRIVATE, MAP_SHARED, or
> | MAP_STACK was specified. At least one of =
these flags
> | must be included.
>=20
> Fabian
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