The manpage for DynaLoader mentions boot_$module names; this is apparently a standard call. From the manpage:

 bootstrap()
           Syntax:
 
           bootstrap($module)
 
           This is the normal entry point for automatic dynamic
           loading in Perl.
 
           It performs the following actions:
 
           ·       locates an auto/$module directory by searching
                   @INC
 
           ·       uses dl_findfile() to determine the filename
                   to load
 
           ·       sets @dl_require_symbols to "("boot_$module")"
 
           ·       executes an auto/$module/$module.bs file if it
                   exists (typically used to add to
                   @dl_resolve_using any files which are required
                   to load the module on the current platform)
 
           ·       calls dl_load_flags() to determine how to load
                   the file.
 
           ·       calls dl_load_file() to load the file
 
           ·       calls dl_undef_symbols() and warns if any sym­
                   bols are undefined
 
           ·       calls dl_find_symbol() for "boot_$module"
 
           ·       calls dl_install_xsub() to install it as
                   "${module}::bootstrap"
 
           ·       calls &{"${module}::bootstrap"} to bootstrap
                   the module (actually it uses the function ref­
                   erence returned by dl_install_xsub for speed)
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