On Wed, Jan 02, 2008 at 10:38:40PM -0800, Jason Evans wrote:
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> Poul-Henning noticed today that xchat fails to start if malloc uses sbrk=
=20
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> internally.  This failure happens during the first call to malloc, with=
=20
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> the following message:
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> Fatal error 'Can't allocate initial thread' at line 335 in file=20
> /usr/src/lib/libthr/thread/thr_init.c (errno =3D 12)
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> This can be worked around with MALLOC_OPTIONS=3DdM .
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> The problem does not appear to be specific to jemalloc; I reverted=20
> src/lib/libc/stdlib/malloc.c to revision 1.92 (last phkmalloc revision),=
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> which also uses sbrk, and the failure mode is the same.
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> The failure occurs on both i386 and amd64.  It appears that sbrk(0)=20
> returns an address that is in the address range normally used by mmap.=20
> So, the first call to sbrk with a non-zero increment is fantastically=20
> wrong.  On i386 (ktrace output):
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>   1013 xchat    CALL  break(0x28200000)
>   1013 xchat    RET   break -1 errno 12 Cannot allocate memory
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> On amd64 (truss ouput):
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>   break(0x800900000)  ERR#12 'Cannot allocate memory'
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> sbrk is not a true system call, so it seems like the problem should have=
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> something to do with the _end data symbol.  I looked at it in gdb though=
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> and never saw an unreasonable value, despite bogus sbrk(0) results.  I=20
> do not know offhand how to get the addresses of .minbrk and .curbrk=20
> (register inspection within gdb while stepping through sbrk?), which are=
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> what sbrk actually uses (see src/lib/libc/amd64/sys/sbrk.S).  Perhaps=20
> the loader isn't initializing them correctly...
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> I am quite pressed for time at the moment, and cannot look into this in=
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> any more detail for at least a couple of weeks.  If anyone knows what=20
> the problem is, please let me know.

I cannot say definitely what happen, but please note that the _end
symbol is defined by linker script, and it shall be present in all
executable and shared objects. The value you reported would be naturally
the _end value for some shared object.

I tried both the RELENG_7 and HEAD, and sbrk(0) correctly returns a
seemingly valid value like 0x8049644.

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>

int
main(int argc, char *argv)
{
	void *p;

	p =3D sbrk(0);
	printf("%p\n", p);

	return (0);
}