Re: [Linux-ia64] Pagesize is different between IA32 and IA64

From: Dugger's <ddugger_at_qwest.net>
Date: 2001-11-14 17:43:55
Never mind, I found the `calloc' code and I'm very depressed because it
does indeed assume that `brk' zeros out newly allocated memory which is
obviously going to create problems if `calloc' thinks the kernel has 4K
pages when it really has bigger ones.

Unfortunately, this means I'll have to make an IA32 specific `brk' call that
zero's out the last part of the last page currently allocated to a process.
Oh well, patch to follow later.
--
Don Dugger
n0ano@indstorage.com
----- Original Message -----
From: "Dugger's" <ddugger@qwest.net>
To: <davidm@hpl.hp.com>; <n0ano@indstorage.com>
Cc: "Hideki Yamamoto" <hideki@hpc.bs1.fc.nec.co.jp>;
<linux-ia64@linuxia64.org>
Sent: Tuesday, November 13, 2001 11:16 PM
Subject: Re: [Linux-ia64] Pagesize is different between IA32 and IA64


> I'm a little confused.  From Hideki's test program the problem actually
> seems
> to be using `sbrk' to return memory and then allocating memory again.  The
> second
> time the re-allocated memory is not zeroed, e.g.:
>
>     p = sbrk(4096);
>     q = sbrk(-4096);
>     r = sbrk(4096);
>
> and the memory pointed to by `r' is not zeroed.  I just got through
reading
> the
> man page for `brk' and `sbrk' and neither one specifies that newly
allocated
> memory is zeroed and therefore I interpret this issue as undefined
behavior.
> Any program that depends upon the contents of newly allocated memory is
> broken.  In fact, if you compile the test program, `d.c', for IA64 and run
> it it
> fails.  Also, if you compile the test program for IA32 and use 1K
allocation
> blocks
> the program fails on an IA32 machine also.
>
> Someone correct me if I'm wrong about this.
>
> PS:  I know that `calloc' is defined to zero out the allocated memory but
> from
> what I can tell it does this by explicitly calling `memset'.  I'm trying
to
> verify this
> but I haven't found the `calloc' code in the `glibc' tree yet.  (The
`glibc'
> tree always
> confuses me, if anyone can tell me exactly where to find the `calloc' code
> I'd
> appreciate it :-)
> --
> Don Dugger
> n0ano@indstorage.com
> ----- Original Message -----
> From: "David Mosberger" <davidm@hpl.hp.com>
> To: <n0ano@indstorage.com>
> Cc: "Hideki Yamamoto" <hideki@hpc.bs1.fc.nec.co.jp>;
> <linux-ia64@linuxia64.org>
> Sent: Monday, November 12, 2001 4:58 PM
> Subject: Re: [Linux-ia64] Pagesize is different between IA32 and IA64
>
>
> > But I think the page size problem with brk() is real and can be fixed
> > quite easily.  If I understood correctly, the problem is that doing
> > something along the lines of:
> >
> > x = ALIGN_TO_4K(sbrk(8192));
> > memset(x, 0xff, 4096);
> > brk(x);
> > brk(x+4096);
> >
> > might preserve the contents of the page at X on under the ia32
> > subsystem of ia64 when in fact it should be cleared to zero.
> >
> > Would you be able/interested into looking into this?
> >
> > --david
> >
>
Received on Tue Nov 13 22:42:10 2001

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