From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "Albert Cahalan" <acahalan@gmail.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: JIT emulator needs
Date: Fri, 8 Jun 2007 12:10:59 +0100 [thread overview]
Message-ID: <20070608121059.4efcd338@the-village.bc.nu> (raw)
In-Reply-To: <787b0d920706072335v10d6025cwe1437194b6c60d84@mail.gmail.com>
> There is an SE Linux execmem restriction that enforces W^X.
This depends on whatever SELinux rulesets you are running. Its just a
good rule to have present that most programs shouldn't be self patching,
and then label those that do differently.
> Sometimes it is very helpful to have the read/write mapping
> be a fixed offset from the read/exec mapping. A power of 2
> can be especially desirable.
mmap MAP_FIXED can do this but you need to know a lot about the memory
layout of the system so it gets a bit platform specific.
> Emulators often need a cheap way to change page permissions.
mprotect(, range) rather than a page at a time. The kernel will do
merging.
> a. sysctl to set IPC_RMID by default
> b. shmget() flag to set IPC_RMID by default
Use POSIX shared memory
> c. open() flag to unlink a file before returning the fd
Is it really that costly to create a blank file, why do you need to do it
a lot in a JIT ?
> e. mremap() flag to get a read/write mapping of a read/exec one
> f. mremap() flag to get a read/exec mapping of a read/write one
> g. mremap() flag to make the 5th arg (new addr) be the upper limit
This is all mprotect and munmap.
> h. 6-bit wide mremap() "flag" to set the upper limit above given base
> i. support the prot argument to remap_file_pages
> j. a documented way (madvise?) to punch same-VMA zero-page holes
mmap (although you get more VMAs from that) so memset() is probably
genuinely cheaper if the permissions are not changing.
next prev parent reply other threads:[~2007-06-08 11:05 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-06-08 6:35 JIT emulator needs Albert Cahalan
2007-06-08 7:09 ` Eric Dumazet
2007-06-09 4:12 ` Albert Cahalan
2007-06-08 11:10 ` Alan Cox [this message]
2007-06-08 16:35 ` Nicholas Miell
2007-06-09 5:17 ` Albert Cahalan
2007-06-09 20:00 ` H. Peter Anvin
2007-06-19 15:08 ` William Lee Irwin III
2007-06-20 3:16 ` Albert Cahalan
2007-06-20 16:01 ` William Lee Irwin III
2007-06-20 16:37 ` H. Peter Anvin
2007-06-20 17:54 ` William Lee Irwin III
2007-06-20 18:23 ` H. Peter Anvin
2007-06-20 18:25 ` Albert Cahalan
2007-06-20 18:51 ` H. Peter Anvin
2007-06-21 3:21 ` Albert Cahalan
2007-06-21 3:32 ` H. Peter Anvin
2007-06-21 7:38 ` Albert Cahalan
2007-06-20 18:43 ` Albert Cahalan
2007-06-23 3:52 ` Kyle Moffett
2007-06-24 4:14 ` William Lee Irwin III
2007-06-21 17:44 ` Arjan van de Ven
2007-06-22 5:56 ` Albert Cahalan
2007-06-22 13:43 ` Arjan van de Ven
2007-06-22 14:32 ` Albert Cahalan
2007-06-22 14:42 ` Arjan van de Ven
2007-06-23 2:30 ` Albert Cahalan
[not found] <8tGiE-2Hv-1@gated-at.bofh.it>
[not found] ` <8xNvm-2Tw-29@gated-at.bofh.it>
[not found] ` <8xYTM-3So-13@gated-at.bofh.it>
2007-06-21 11:08 ` Bodo Eggert
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