From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Hideki Yamamoto" Date: Wed, 14 Nov 2001 07:00:06 +0000 Subject: Re: [Linux-ia64] Pagesize is different between IA32 and IA64 Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org Hi Don. Thank you very much! I greatly appreciate your kindness. At Tue, 13 Nov 2001 23:43:55 -0700, Dugger's wrote: > > 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" > To: ; > Cc: "Hideki Yamamoto" ; > > 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" > > To: > > Cc: "Hideki Yamamoto" ; > > > > 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 > > > > > > > > _______________________________________________ > Linux-IA64 mailing list > Linux-IA64@linuxia64.org > http://lists.linuxia64.org/lists/listinfo/linux-ia64 >