Python 2.5a1 and Python 2.4.3 both build incorrectly on
Solaris 8 when compiled in 64-bit mode, using Sun
Studio 11 cc.  Here is the diagnostic:

cc -O -xarch=v9 -G
build/temp.solaris-2.8-sun4u-2.5/cryptmodule.o
-L/u/cs/fac/eggert/seasnet/prefix/lib -lcrypt -o
build/lib.solaris-2.8-sun4u-2.5/crypt.so
ld: fatal: library -lcrypt: not found
ld: fatal: File processing errors. No output written to
build/lib.solaris-2.8-sun4u-2.5/crypt.so

The problem is that setup.py looks at 32-bit libraries
when trying to decide whether a 64-bit build will work.
 Using LIBS=' -lcrypt_i' does not work around the
problem, since the LIBS setting is not exported to the
module build.  I'll attach a proposed patch to the
README file to warn about the problem.

Paul, your comment in your patch, about this being fixed post Solaris 9,
doesn't appear to be correct.  I have x86_64-sun-solaris2.10 with all
patches applied and the problem exists there too.  I'm using Workshop 12.

I use this patch, which just always uses crypt_i on Solaris to work around the problem.

I've no idea whether or not the patches are still valid after all this time.

While I have not tested the patch provided, the following ls(1) command on Sun Solaris 10 Update 8 and Oracle Solaris 10 Update 11, show that on (at least) X86 systems, there is no -lcrypt for 64-bit builds. So a patch is required on 64-bit builds, and possibly 32-bit builds if library variant (_d vs _i) consistency is required.

% ls -l /usr/lib/**/libcrypt* | sed -e 's/ 1 root .* 20.. //'

lrwxrwxrwx  /usr/lib/amd64/libcrypt_d.so -> ./libcrypt_d.so.1
-rwxr-xr-x  /usr/lib/amd64/libcrypt_d.so.1
lrwxrwxrwx  /usr/lib/amd64/libcrypt_i.so -> libcrypt_i.so.1
-rwxr-xr-x  /usr/lib/amd64/libcrypt_i.so.1
lrwxrwxrwx  /usr/lib/amd64/libcryptoutil.so -> libcryptoutil.so.1
-rwxr-xr-x  /usr/lib/amd64/libcryptoutil.so.1
lrwxrwxrwx  /usr/lib/libcrypt.so -> libcrypt_d.so
lrwxrwxrwx  /usr/lib/libcrypt.so.1 -> libcrypt_d.so.1
lrwxrwxrwx  /usr/lib/libcrypt_d.so -> ./libcrypt_d.so.1
-rwxr-xr-x  /usr/lib/libcrypt_d.so.1
lrwxrwxrwx  /usr/lib/libcrypt_i.so -> ./libcrypt_i.so.1
-rwxr-xr-x  /usr/lib/libcrypt_i.so.1
lrwxrwxrwx  /usr/lib/libcryptoutil.so -> ./libcryptoutil.so.1
-rwxr-xr-x  /usr/lib/libcryptoutil.so.1

PS: Solaris 11.2 (X86) on the other hand does have a -lcrypt for both 32-bit and 64-bit libraries (libcrypt.so -> ./libcrypt.so.1)

Python 2.4 and 2.5 are no longer maintained. Please create a new issue if you are seeing this problem on a current version (>= 3.9).