Date: Wed, 28 Jan 2009 14:20:54 +0200 From: Danny Braniss <danny@cs.huji.ac.il> To: Channa <channa.kad@gmail.com> Cc: Christoph Mallon <christoph.mallon@gmx.de>, freebsd-current@freebsd.org Subject: Re: Jemalloc SEGV for 1MB chunk Message-ID: <E1LS9Pa-000NBW-Ct@kabab.cs.huji.ac.il> In-Reply-To: <515c64960901280401w1e1d08bfx29adc124bc749c4a@mail.gmail.com> References: <515c64960901280339m17fa9309v2e1bc3f55454ab@mail.gmail.com> <49804597.6040303@gmx.de> <515c64960901280401w1e1d08bfx29adc124bc749c4a@mail.gmail.com>
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> Hi,
> Thanks for your reply.
> You mean to say i should modify the test as below:
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
>
>
> int main()
> {
> int i;
> char *buf;
> size_t size = 1048576 ;
>
> buf = malloc(size);
> for (i = 0; i <= 1048575; i++)
> buf[i] = 'a';
> buf[size]='\0';
> printf("The length of buff is : %d\n",strlen(buf));
> free(buf);
> return 0;
> }
>
> I NULL terminated the string
> buf[size] = '\0' <== The last character is NULL
>
> But still i get a SEGV at strlen.
>
> Could you please tell me if my changes above are correct?
>
clear case of off by one.
you are requesting 'size' bytes, indexing starts at 0, all the way to size-1
which is ALL the bytes you malloc'ed
then you zero the size+1 byte, ah, btw, it's not strlen that is SEGV'ing.
danny
> Regards,
> Channa
>
>
> On 28/01/2009, Christoph Mallon <christoph.mallon@gmx.de> wrote:
> > Channa schrieb:
> >
> >
> > > Hi All,
> > > I am using jemalloc.c source from FreeBSD-current source.
> > > When i allocate 1MB of memory using malloc() and use it as the below
> > > test shows
> > >
> > > #include <stdio.h>
> > > #include <stdlib.h>
> > > #include <string.h>
> > >
> > > int main()
> > > {
> > > int i;
> > > char *buf;
> > > size_t size = 1048576 ;
> > >
> > > buf = malloc(size);
> > > for (i = 0; i < 1048576; i++)
> > > buf[i] = 'a';
> > > printf("The length of buff is : %d\n",strlen(buf));
> > > free(buf);
> > > return 0;
> > > }
> > >
> > > When i try to call strlen(buf) SEGV is recived.
> > >
> > > This behaviour is seen when only for 1MB chunk if i allocate
> > > memory lesser than 1MB no issues noticed.
> > >
> > > Could anyone see similar problem?
> > > Is the above test wrong?
> > > Or some issue with huge memory allocation in jemalloc?
> > >
> > > Your response will be very helpful.
> > >
> > > Thanks & Regards,
> > > Channa
> > >
> >
> > You did not NUL-terminate ('\0') the string.
> >
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