Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 13 Dec 2001 11:24:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 13 Dec 2001 11:23:54 -0500 Received: from shimura.Math.Berkeley.EDU ([169.229.58.53]:62868 "EHLO shimura.math.berkeley.edu") by vger.kernel.org with ESMTP id ; Thu, 13 Dec 2001 11:23:31 -0500 Date: Thu, 13 Dec 2001 08:22:51 -0800 (PST) From: Wayne Whitney Reply-To: To: Petr Vandrovec cc: LKML Subject: Re: Repost: could ia32 mmap() allocations grow downward? In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 13 Dec 2001, Petr Vandrovec wrote: > If you have legacy app, how it comes that it uses mmap? Very good question. The app per se does not call mmap(), but mmap() is called once when I execute it. So it must be something from libc: [whitney@mf1 whitney]$ ldd `which magma` not a dynamic executable [whitney@mf1 whitney]$ magma [ . . .] [2]+ Stopped magma [whitney@mf1 whitney]$ cat /proc/`pidof magma`/maps 08048000-08afb000 r-xp 00000000 21:07 64318 magma 08afb000-08c3e000 rw-p 00ab2000 21:07 64318 magma 08c3e000-0bc54000 rwxp 00000000 00:00 0 40000000-40001000 rw-p 00000000 00:00 0 bfffd000-c0000000 rwxp ffffe000 00:00 0 > So maybe MAGMA uses some API which it should not use under any > circumstances... Such as that you linked it with libc6 stdio. Indeed. How can I avoid the map at 0x40000000? Must I avoid using certain glibc2 functions, and then link the executable carefully to leave out their initialization routines? Or can I set some magic environment variable to tell glibc2 to mmap() the single map with MAP_FIXED at a higher addresss? Of course I could modify glibc2 so that it does all (or most) of its mmap()'s with MAP_FIXED at a higher address. Is there an alternative libc that might work out of the box or require less modification? So it seems like for MAGMA I should be able to work around the fact that mmap()'s start at 0x40000000. But as difficulties with other programs come up here fairly regularly, I still think it makes sense to fully understand the downside of modifying the kernel to allocate mmap() VMAs going downward. If the downside is small, I think it is a good tradeoff. Cheers, Wayne - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/