On Tue, Sep 09, 2008 at 02:49:18AM +0200, Henrik Johansson wrote:
> Hello all,
>
> I saw this question about a year back in the archive[1], but with no
> final answer.
>
> I would like to trace shmget calls and also get the id of the shared
> memory segment.
>
> That script looked like[2], but we dont get the id since arg1 is the
> errno value.
>
> How do i access the shm id, i would need this to debug a customer
> problem but i don't have time to learn it the hard way.
If you look at the arguments of shmget:
# dtrace -lv -n fbt::shmget:
ID PROVIDER MODULE FUNCTION NAME
79745 fbt shmsys shmget entry
Probe Description Attributes
Identifier Names: Private
Data Semantics: Private
Dependency Class: Unknown
Argument Attributes
Identifier Names: Private
Data Semantics: Private
Dependency Class: ISA
Argument Types
args[0]: key_t
args[1]: size_t
args[2]: int
args[3]: uintptr_t *
79746 fbt shmsys shmget return
Probe Description Attributes
Identifier Names: Private
Data Semantics: Private
Dependency Class: Unknown
Argument Attributes
Identifier Names: Private
Data Semantics: Private
Dependency Class: ISA
Argument Types
args[0]: int
args[1]: int
and the code for shmsys:
http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/os/shm.c#shmsys
static uintptr_t
shmsys(int opcode, uintptr_t a0, uintptr_t a1, uintptr_t a2)
{
int error;
uintptr_t r_val = 0;
switch (opcode) {
...
case SHMGET:
error = shmget((key_t)a0, (size_t)a1, (int)a2, &r_val);
break;
...
}
if (error)
return ((uintptr_t)set_errno(error));
return (r_val);
}
You'll see that the return value is passed through a pointer in the fourth
argument. The simplest way to change your script is to do:
--- cut here ---
#!/usr/sbin/dtrace -s
#pragma D option quiet
dtrace:::BEGIN
{
/* operation key shmid size flags cpu wall */
printf("%-10s %-10s %-10s %-10s %-10s %-10s %-10s\n", "operation",
"key", "shmid",
"size", "flags",
"CPU", "Wall Time");
}
fbt::shmget:entry
{
self->key = args[0];
self->size = args[1];
self->flags = args[2];
self->shmidp = args[3];
self->shmgettimestamp = timestamp;
self->shmgetvtimestamp = vtimestamp;
}
fbt::shmget:return
/ self->shmgettimestamp /
{
/* operation key shmid size flags cpu wall */
printf("%-10s %-10x %-10x %-10d %-10d %-10d %-10d\n", probefunc,
self->key, *self->shmidp,
self->size, self->flags,
vtimestamp - self->shmgetvtimestamp,
timestamp - self->shmgettimestamp);
}
--- cut here ---
Note that I've switched to using args[n] probes, instead of argn. For FBT
probes, this makes sure the types work correctly.
Cheers,
- jonathan
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