Date: Mon, 25 Jun 2007 10:54:06 +0200 (CEST) From: =?iso-8859-1?Q?Bj=F6rn_K=F6nig?= <bkoenig@alpha-tierchen.de> To: hackers@freebsd.org Subject: end, edata, etext issues Message-ID: <1500.192.168.1.2.1182761646.squirrel@webmail.alpha-tierchen.de>
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Hello,
I'm playing with FreeBSD on ARM. I noticed that sbrk(2) doesn't work
properly on this architecture. I still don't understand the whole process
of the initialisation of end, edata and etext. There are some oddities
that confuse me even more. Let me make an example:
1 #include <stdio.h>
2 extern end;
3 extern edata;
4 int main() {
5 printf("edata: %08x\n", edata);
6 printf("end: %08x\n", end);
7 printf("sbrk(0): %08x\n", sbrk(0));
8 return (0);
9 }
> cc test.c && ./a.out
edata: 00000000
end: 00000000
sbrk(0): ffffffff
This is obviously not correct and the reason why program that rely sbrk(2)
are broken. I added the following code:
1 .data
2 .globl curbrk
3 curbrk:
4 .word end
and compiled the whole thing again:
> cc test.c curbrk.S && ./a.out
edata: 00000000
end: 0001070c
sbrk(0): 00100000
and it seems to work.
Another strange thing is that if I don't access "edata", e.g. leave
printf("edata: %08x\n", edata); away, then sbrk still works, but "end"
is zero. In case I don't access "edata" or "end" at all I'll get a bus
error.
Is there somebody who can tell me how end depends on the presence curbrk
and edata in this example?
Regards
Björn
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