Date: Tue, 11 Apr 2017 00:16:59 -0700 From: Christopher Bowman <crb@chrisbowman.com> To: hackers@freebsd.org Subject: Dtrace oddity Message-ID: <CD5E9B03-6147-4E4D-BED6-6C45022051E3@chrisbowman.com>
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Apologies if I=E2=80=99m sending to the wrong list. I have a small test =
program shown at the bottom. It tries to mmap a device for which I=E2=80=99=
ve written (a possibly incorrect) driver. When I run the program I get =
the following output: =20
crb@retread:63> ./test /dev/sp6050=20
argc =3D 2
argv[0] =3D ./test
argv[1] =3D /dev/sp6050
opening device /dev/sp6050
open returned non-zero value
mmap failed: EINVAL
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:
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
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.
Here is my program:
/*
Copyright (c) 2011 by Christopher R. Bowman. All rights =
reserved.
*/
#include <errno.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/mman.h>
int main (int argc, char ** argv) {
int i;
printf("argc =3D %d\n", argc);
for (i=3D0; i < argc; i++)
printf ("argv[%i] =3D %s\n", i, argv[i]);
if (argc < 2) {
printf("usage: test device\n");
return 0;
}
printf("opening device %s\n", argv[1]);
int device =3D open (argv[1], O_RDWR);
if (device =3D=3D 0) {
printf ("open of device %s failed\n", argv[1]);
return 0;
}
printf("open returned non-zero value\n");
void *pa =3D mmap (0, 4095, PROT_READ | PROT_WRITE, 0, device, =
0);
if (pa =3D=3D MAP_FAILED) {
printf ("mmap failed: ");
switch (errno) {
case EACCES: printf("EACCESS\n"); break;
case EBADF: printf("EBADF\n"); break;
case EINVAL: printf("EINVAL\n"); break;
case ENODEV: printf("ENODEV\n"); break;
case ENOMEM: printf("ENOMEM\n"); break;
}
return 0;
}
printf("mmap returned non-zero value: %lx\n", (unsigned =
long)pa);
unsigned int *p =3D (unsigned int *) pa;
unsigned char *c =3D (unsigned char *) pa;
#define NUM_ITERATIONS 16
for (i=3D0; i < NUM_ITERATIONS; i++){ //BARs are 2Kbytes
//*p++ =3D (0xa5a5 + i);
*p++ =3D (0x5aa5a5a5);
}
p =3D (unsigned int *) pa;
for (i=3D0; i < NUM_ITERATIONS; i++){
printf("i =3D %d, read_val =3D %x\n", i, *p++);
}
}
Thanks in advance for comments on Dtrace or perhaps program corrections =
or ideas why the mmap failed or places to read on kernel debugging or =
pointers to a better list to which to send this.
Thanks
Christopher
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