AMD64 only Segmentation fault (was: 7-STABLE(AMD64)+Qmail-LDAP core dump)

Xin LI delphij at
Mon Mar 3 22:52:08 UTC 2008

Alexandre Biancalana wrote:
> Hi list,
>   I found a situation that I can't explain, I have qmail-ldap running
> at some FreeBSD 6.2 without any problem. Friday after Installed a new
> server this time with 7-STABLE. I stated to get core dumped from
> qmail-ldap when they try access the OpenLDAP database.
>  I compiled/run this simple C program in 7-STABLE i386 and AMD64 and
> the program dumps the core only in AMD64.

I have tried to reproduce the problem and have the following 
observations.  To make a long story short, you *must* either use the new 
ldap_initialize API instead of the old one, or to define LDAP_DEPRECATED 
at the risk of having the program to break in the future, and *NOT* 
ignoring any warnings issued by the compiler.

So here is the reason why we have a coredump.  ldap_init is defined only 
when LDAP_DEPRECATED is defined, when ldap.h is included, and by 
default, C will assume that the return type is "int".

On i386, this is not a problem because sizeof(int) equals to sizeof(void 
*), and the implicit cast would work;  On amd64, we have sizeof(int) == 
4 and sizeof(void *) == 8, by casting the result to int (because the 
header did not gave the type of ldap_init), and back (because of the 
assignment ld =), we lose 4 bytes (the high 32 bits) of the pointer, and 
therefore, when referring it we got a SEGV.

This is one of the most common culprit when your 32-bit application 
"magically" broken on amd64 :-)

Xin LI <delphij at>
FreeBSD - The Power to Serve!

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