GNU Info

(make.info)Missing

---

Next: Makefile Conventions Prev: Features Up: Top

---

Enter node , (file) or (file)node

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
     nonmodularity of putting knowledge into `make' of the internal
     format of archive file symbol tables.  Note: Updating Archive
     Symbol Directories.

   * 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 `make', the string `$$@' has the strange meaning that,
     in the prerequisites of a rule with multiple targets, it stands
     for the particular target that is being processed.

     This is not defined in GNU `make' because `$$' should always stand
     for an ordinary `$'.

     It is possible to get portions of this functionality through the
     use of static pattern rules (Note: Static Pattern Rules.
).  The System V `make' rule:

          $(targets): $$@.o lib.a

     can be replaced with the GNU `make' static pattern rule:

          $(targets): %: %.o lib.a

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

   * 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.) is apparently done for _all_ targets, not
     just those without commands.  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 commands, and it is treated as if it had empty commands (Note:
     Empty Commands).  For example:

          .c.a:

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

     We feel that it is cleaner for a rule without commands 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 shell command line to stand on its own and not require
     this special treatment.