Re: ps_strings
http://forums.freebsd.org/showthread.php?p=228128 http://www.dolphinburger.com/cgi-bin/bsdi-man?proto=1.1query=ps_stringsmsection=5apropos=0 On Sat, Aug 17, 2013 at 2:00 PM, Carlos Jacobo Puga Medina cjpug...@gmail.com wrote: Hi people, Despite I made a request not long ago[1], I'm looking for documentation to create the ps_strings structure man page because isn't covered in other man page such e.g. execve(2). So, I'm interested to know for what it's currently used. Any input will be appreciated. --CJPM [1] http://lists.freebsd.org/pipermail/freebsd-doc/2013-July/022422.html. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: ps_strings
On Sat, Aug 17, 2013 at 8:00 PM, Carlos Jacobo Puga Medina cjpug...@gmail.com wrote: Hi people, Despite I made a request not long ago[1], I'm looking for documentation to create the ps_strings structure man page because isn't covered in other man page such e.g. execve(2). So, I'm interested to know for what it's currently used. Any input will be appreciated. It is for storing the vectors for program arguments and environment. They are placed at the top of the process stack. This information is used for instance, by the ps(1) program via the kvm(3) interface. The same structure is accesed from the linuxolator (linprocfs.c) to implement the environ pseudo-file. In the first case (libkvm interface) a sysctl is used to retrieve that information. Anyway, both paths end up calling proc_getenvv/proc_getargv in kern_proc.c. Those are selectors for the function that does the actual work: get_ps_strings. This function first calls get_proc_vector to copy the relevant memory area (look for vptr in the case statement) from the process stack and then it iterates to extract all the strings. Have a look at the comment in sys/exec.h All this is probably not needed for the man page, but hey, just my two cents. --CJPM [1] http://lists.freebsd.org/pipermail/freebsd-doc/2013-July/022422.html. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: ps_strings
Despite I made a request not long ago[1], I'm looking for documentation to create the ps_strings structure man page because isn't covered in other man page such e.g. execve(2). So, I'm interested to know for what it's currently used. Nothing. (Well, backwards compatibility, depending on how far backwards you go.) I invented the ps_strings struct a long time ago, about the same time libkvm was new. Some background: There was code in ps that would grub around in the top stack page of each user process and extract the argv strings. This code knew how execve() worked inside the kernel (copying the argv and environment strings into the user stack, just below the signal trampoline code, and then setting up argv and envp pointers and invoking the libc/csu start program code at the entry point). We moved this grub-around-in-process-stack code to libkvm, but it was still rather horrible code. Meanwhile, we had programs like sendmail that would set their process title by saving, in some secret global variable, the space where the argv array itself and its strings lived, and then -- in setproctitle() -- carefully overwrite it. Of course there was only as much room there as the kernel provided, based on the actual strings at execve() time. I figured this would all be much cleaner if we created a small data structure, namely ps_strings, to hold the information that libkvm would extract (and hence, ps would show). It would be simpler than the original code, because the ps_strings structure lived at a fixed, well known user-space virtual address (the same VA in every process). Moreover, a user program (like sendmail) could modify the ps_strings data to point to any other user-space area: libkvm was smart enough to extract arbitrary data (and verify the validity of the address too). This removed the limit on how large a process title could be. FreeBSD now, however, uses a per-process p_args field in the proc structure, with sysctl()s to set and get p_args. (I had nothing to do with this new code, but I approve, as if anyone cares. :-) ) This removes the fixed-virtual-address limitation. The cost is a bit more kernel code (for the sysctl()s) and this per-process data, but there is no more messing-about with where is ps_strings in this memory-layout / emulation etc. (Meanwhile libkvm still retrieves the arguments. It just does it now with sysctl().) Chris ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
