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

From: Dugger's <ddugger_at_qwest.net>
Date: 2001-11-14 17:16:09
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 22:14:31 2001

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