Re: About reading /proc/*/mem

[Alexander Viro <viro@math.psu.edu>]

On Tue, 1 May 2001, Richard F Weber wrote:

> See this is where I start seeming to have problems.  I can open 
> /proc/*/mem & lseek, but reads come back as "No such process".  However, 
> if I first do a ptrace(PTRACE_ATTACH), then I can read the data, but the 
> process stops.  I've kind of dug through the sys_ptrace() code under 
> /usr/src/linux/arch/i386/kernel/ptrace.c, and can see and understand 
> generally what it's doing, but that's getting into serious kernel-land 
> stuff.  I wouldn't expect it to be this difficult to just open up 
> another processes /proc/*/mem file to read data from.
 
> Is there something obvious I'm missing?  It seems to keep pointing back 
> to ptrace & /proc/*/mem are very closely related (ie: the same) 
> including stopping of the child.

OK, here's something I really don't understand. Suppose that I tell your
debugger to tell me when in the executed program foo becomes greater than
bar[0] + 14. Or when cyclic list foo becomes longer than 1 element
(i.e. foo.next != foo.prev).

How do you do that if program is running? If you don't guarantee that
it doesn't run during the access to its memory (moreover, between sever
such accesses) - the data you get is worthless.

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