Info Catalog make: Environment make: Using Variables make: Pattern-specific

make: Target-specific

 
 6.11 Target-specific Variable Values
 ====================================
 
 Variable values in 'make' are usually global; that is, they are the same
 regardless of where they are evaluated (unless they're reset, of
 course).  One exception to that is automatic variables (Automatic
 Variables).
 
    The other exception is "target-specific variable values".  This
 feature allows you to define different values for the same variable,
 based on the target that 'make' is currently building.  As with
 automatic variables, these values are only available within the context
 of a target's recipe (and in other target-specific assignments).
 
    Set a target-specific variable value like this:
 
      TARGET ... : VARIABLE-ASSIGNMENT
 
    Target-specific variable assignments can be prefixed with any or all
 of the special keywords 'export', 'override', or 'private'; these apply
 their normal behavior to this instance of the variable only.
 
    Multiple TARGET values create a target-specific variable value for
 each member of the target list individually.
 
    The VARIABLE-ASSIGNMENT can be any valid form of assignment;
 recursive ('='), simple (':=' or '::='), appending ('+='), or
 conditional ('?=').  All variables that appear within the
 VARIABLE-ASSIGNMENT are evaluated within the context of the target:
 thus, any previously-defined target-specific variable values will be in
 effect.  Note that this variable is actually distinct from any "global"
 value: the two variables do not have to have the same flavor (recursive
 vs. simple).
 
    Target-specific variables have the same priority as any other
 makefile variable.  Variables provided on the command line (and in the
 environment if the '-e' option is in force) will take precedence.
 Specifying the 'override' directive will allow the target-specific
 variable value to be preferred.
 
    There is one more special feature of target-specific variables: when
 you define a target-specific variable that variable value is also in
 effect for all prerequisites of this target, and all their
 prerequisites, etc. (unless those prerequisites override that variable
 with their own target-specific variable value).  So, for example, a
 statement like this:
 
      prog : CFLAGS = -g
      prog : prog.o foo.o bar.o
 
 will set 'CFLAGS' to '-g' in the recipe for 'prog', but it will also set
 'CFLAGS' to '-g' in the recipes that create 'prog.o', 'foo.o', and
 'bar.o', and any recipes which create their prerequisites.
 
    Be aware that a given prerequisite will only be built once per
 invocation of make, at most.  If the same file is a prerequisite of
 multiple targets, and each of those targets has a different value for
 the same target-specific variable, then the first target to be built
 will cause that prerequisite to be built and the prerequisite will
 inherit the target-specific value from the first target.  It will ignore
 the target-specific values from any other targets.
 

Info Catalog make: Environment make: Using Variables make: Pattern-specific