+=head2 Overriding an old config.sh
+
+If you want to use your old config.sh but override some of the items
+with command line options, you need to use B<Configure -O>.
+
+=head2 GNU-style configure
+
+If you prefer the GNU-style configure command line interface, you can
+use the supplied configure.gnu command, e.g.
+
+ CC=gcc ./configure.gnu
+
+The configure.gnu script emulates a few of the more common configure
+options. Try
+
+ ./configure.gnu --help
+
+for a listing.
+
+(The file is called configure.gnu to avoid problems on systems
+that would not distinguish the files "Configure" and "configure".)
+
+See L<Cross-compilation> below for information on cross-compiling.
+
+=head2 Malloc Issues
+
+Perl relies heavily on malloc(3) to grow data structures as needed,
+so perl's performance can be noticeably affected by the performance of
+the malloc function on your system. The perl source is shipped with a
+version of malloc that has been optimized for the typical requests from
+perl, so there's a chance that it may be both faster and use less memory
+than your system malloc.
+
+However, if your system already has an excellent malloc, or if you are
+experiencing difficulties with extensions that use third-party libraries
+that call malloc, then you should probably use your system's malloc.
+(Or, you might wish to explore the malloc flags discussed below.)
+
+=over 4
+
+=item Using the system malloc
+
+To build without perl's malloc, you can use the Configure command
+
+ sh Configure -Uusemymalloc
+
+or you can answer 'n' at the appropriate interactive Configure prompt.
+
+=item -DPERL_POLLUTE_MALLOC
+
+NOTE: This flag is enabled automatically on some platforms if you just
+run Configure to accept all the defaults on those platforms.
+
+Perl's malloc family of functions are normally called Perl_malloc(),
+Perl_realloc(), Perl_calloc() and Perl_mfree().
+These names do not clash with the system versions of these functions.
+
+If this flag is enabled, however, Perl's malloc family of functions
+will have the same names as the system versions. This may be required
+sometimes if you have libraries that like to free() data that may have
+been allocated by Perl_malloc() and vice versa.
+
+Note that enabling this option may sometimes lead to duplicate symbols
+from the linker for malloc et al. In such cases, the system probably
+does not allow its malloc functions to be fully replaced with custom
+versions.
+
+=item -DPERL_DEBUGGING_MSTATS
+
+This flag enables debugging mstats, which is required to use the
+Devel::Peek::mstat() function. You cannot enable this unless you are
+using Perl's malloc, so a typical Configure command would be
+
+ sh Configure -Accflags=-DPERL_DEBUGGING_MSTATS -Dusemymalloc='y'
+
+to enable this option.
+
+=back
+