Re: sysctl.proc_exec_affinity to force launching of 32-bit flavor?
Re: sysctl.proc_exec_affinity to force launching of 32-bit flavor?
- Subject: Re: sysctl.proc_exec_affinity to force launching of 32-bit flavor?
- From: Terry Lambert <email@hidden>
- Date: Thu, 12 Mar 2009 11:20:35 -0700
On Mar 12, 2009, at 5:54 AM, Jim Correia <email@hidden> wrote:
On Mar 12, 2009, at 6:10 AM, Terry Lambert wrote:
The place where this would be important today is on a machine
capable of running 64 bit Intel binaries, but for which only the
system framework is available, and not other frameworks. Since we
changed the 64 bit binary cpu type number by adding a "has 64 bit
frameworks bit" to it, when we added framework support, if you link
a new binary, the 386 version of the binary is going to be
preferred by the older version of the OS anyway, so you'd be
solving a problem that doesn't exist in the first place.
The other place it could be important is if you ported over your 32
bit KEXT or daemon that talked to it, and decide, for whatever
reason that you wanted to still communicate ponter and long values
between it and user space instead of using sized types.
The other place where I wanted to control this is where my GUI app,
which runs as a 32-bit process on Leopard (which can be influenced
by LSMinimumSystemVersionByArchitecture), launches a helper (today
via exec), and I'd like to run the helper as 32-bit on Leopard too,
mainly because I don't want to be the reason the 64-bit frameworks
are loaded in.
For a drag and drop type install, LIPO isn't an option.
FWIW:
If it knows enough to know that it wants to exec a lower graded binary
slice of itself, it could lipo and exec just as easily as it could do
the specific exec of the lower graded slice from the higher graded
slice. Another alternative is a small helper program that is pointed
to by the plist that repoints it at either the 32 or 64 bit binary
rather than itself the first time it's run, thus avoing the overhead
on subsequent runs.
The only place a first-time-you-run approach isn't appropriate is if
you are loading off network storage shared between systems with
conflicting requirements (unlikely for KEXTs, but possible). A small
helper binary that sticks around rather than repointing things and
execs daemon32 or daemon64 as appropriate still works for that case,
though.
-- Terry
But you could also LIPO at install time with your install tool or
the binary itself when it saw the results of the uname(2) system
call, or you could also write a small script to wrap the use of the
arch(1) command, or you could use the posix_spawn(2) extensions
documented in posix_spawnattr_setbinpref_np(2) to reexec yourself,
if you didn't mind running the 64 bit binary, saying "whoops! I
should be 32 bit!" and restarting yourself with a different
preference.
It looks like using posix_spawn solves the problem. (Previously I
was using fork/exec because the code was originally written to
target 10.4.x.)
- Jim
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