Makefiles and compilation rules

• The input file for the make command MUST be named Makefile, with a capital "M".

  Rationale: although the latter name makefile is also valid, common usage prefer the former.

• The Makefile (provided or generated by configure) SHOULD contain the all, clean and distclean rules.
• The Makefile MUST NOT use non-standard syntax. In particular, it MUST NOT expect to be parsed by GNU make ("gmake").
• The default rule MUST be the all rule.
• The clean rule SHOULD clear object files, temporaries and automatic editor backups from the source tree.
• The distclean rule MUST depend on the clean rule, and SHOULD clear executables, shared objects and library archives from the source tree.
• The use of so-called "recursive Makefiles" is discouraged; when used, the amount of redundancy between Makefiles SHOULD be kept low by proper use of include directives.
• C sources MUST compile without warnings when using strict compilers. The GNU C compiler, when provided with strict warning options, is considered a strict compiler for this purpose.

  Especially, when GCC is available as a standard compiler on a system, source code MUST compile with GCC and the following options:

             -Wall -W -ansi -Werror
            

  Additionally, it SHOULD compile without warnings with GCC and the following options (all documented in the GCC manual page):

             -Wall -W -ansi -pedantic
             -Wfloat-equal -Wundef -Wshadow -Wpointer-arith
             -Wbad-function-cast -Wcast-qual -Wcast-align
             -Waggregate-return -Wstrict-prototypes -Wmissing-prototypes
             -Wmissing-declarations -Wnested-externs
             -Wunreachable-code
            

• The previous requirement does not imply that the Makefile must actually use these flags. It does not imply that GCC must be always used: only the command cc is guaranteed to be available, and may point to a different compiler.
• C compilation rules SHOULD use the warning flag specifiers when possible.
• Makefile rules MUST NOT expect the presence of GCC on all target architectures.
• As a side effect of the two previous rules, compiler differences and architecture-dependent flags MUST be handled by appropriate use of the uname command. In particular, the environment variable HOSTTYPE MUST NOT be used for this purpose, since it has a shell-dependant and architecture-dependent behaviour.