File: make.info,  Node: Missing,  Next: Makefile Conventions,  Prev: Features,  Up: Top

15 Incompatibilities and Missing Features
*****************************************

The 'make' programs in various other systems support a few features that
are not implemented in GNU 'make'.  The POSIX.2 standard ('IEEE Standard
1003.2-1992') which specifies 'make' does not require any of these
features.

   * A target of the form 'FILE((ENTRY))' stands for a member of archive
     file FILE.  The member is chosen, not by name, but by being an
     object file which defines the linker symbol ENTRY.

     This feature was not put into GNU 'make' because of the
     non-modularity of putting knowledge into 'make' of the internal
     format of archive file symbol tables.  *Note Updating Archive
     Symbol Directories: Archive Symbols.

   * Suffixes (used in suffix rules) that end with the character '~'
     have a special meaning to System V 'make'; they refer to the SCCS
     file that corresponds to the file one would get without the '~'.
     For example, the suffix rule '.c~.o' would make the file 'N.o' from
     the SCCS file 's.N.c'.  For complete coverage, a whole series of
     such suffix rules is required.  *Note Old-Fashioned Suffix Rules:
     Suffix Rules.

     In GNU 'make', this entire series of cases is handled by two
     pattern rules for extraction from SCCS, in combination with the
     general feature of rule chaining.  *Note Chains of Implicit Rules:
     Chained Rules.

   * In System V and 4.3 BSD 'make', files found by 'VPATH' search
     (*note Searching Directories for Prerequisites: Directory Search.)
     have their names changed inside recipes.  We feel it is much
     cleaner to always use automatic variables and thus make this
     feature unnecessary.

   * In some Unix 'make's, the automatic variable '$*' appearing in the
     prerequisites of a rule has the amazingly strange "feature" of
     expanding to the full name of the _target of that rule_.  We cannot
     imagine what went on in the minds of Unix 'make' developers to do
     this; it is utterly inconsistent with the normal definition of
     '$*'.

   * In some Unix 'make's, implicit rule search (*note Using Implicit
     Rules: Implicit Rules.) is apparently done for _all_ targets, not
     just those without recipes.  This means you can do:

          foo.o:
                  cc -c foo.c

     and Unix 'make' will intuit that 'foo.o' depends on 'foo.c'.

     We feel that such usage is broken.  The prerequisite properties of
     'make' are well-defined (for GNU 'make', at least), and doing such
     a thing simply does not fit the model.

   * GNU 'make' does not include any built-in implicit rules for
     compiling or preprocessing EFL programs.  If we hear of anyone who
     is using EFL, we will gladly add them.

   * It appears that in SVR4 'make', a suffix rule can be specified with
     no recipe, and it is treated as if it had an empty recipe (*note
     Empty Recipes::).  For example:

          .c.a:

     will override the built-in '.c.a' suffix rule.

     We feel that it is cleaner for a rule without a recipe to always
     simply add to the prerequisite list for the target.  The above
     example can be easily rewritten to get the desired behavior in GNU
     'make':

          .c.a: ;

   * Some versions of 'make' invoke the shell with the '-e' flag, except
     under '-k' (*note Testing the Compilation of a Program: Testing.).
     The '-e' flag tells the shell to exit as soon as any program it
     runs returns a nonzero status.  We feel it is cleaner to write each
     line of the recipe to stand on its own and not require this special
     treatment.