Re: patches to actually use markers?

[fche at redhat dot com (Frank Ch. Eigler)]

Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> writes:

> [...]
>>   trace_mark(kernel_arch_syscall_entry, "syscall_id %d ip #p%ld",
>> 			(int)regs->orig_eax, instruction_pointer(regs));
>> [...]
>> For systemtap use, we'd like to have more information than that.  On
>> syscall entry, we'd like be able to get the arguments, [...]
>
> Well, the approach taken was to instrument each important system call in
> the syscall specific function to be able to actually know what type of
> information to record. For instance, if ebx points to a string, the
> pointer is not very useful, but the string is.

How would this syscall specific function get ebx or the string,
without ebx (or regs) being passed as marker arguments?

For systemtap's purposes, we're prepared to have per-systemcall logic
to decode arguments further, in particular to extract user-space
strings.  But we need to know where to look for them!


> You have a good point for the syscall exit instrumentation : adding the
> return value is trivial and would be very useful.

(And an errno code if it's separate.)


- FChE