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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/make.texi | 59 |
1 files changed, 48 insertions, 11 deletions
diff --git a/doc/make.texi b/doc/make.texi index c2ae06a..82df90a 100644 --- a/doc/make.texi +++ b/doc/make.texi @@ -5720,12 +5720,7 @@ In addition to target-specific variable values (@pxref{Target-specific, ,Target-specific Variable Values}), GNU @code{make} supports pattern-specific variable values. In this form, the variable is defined for any target that matches the pattern -specified. If a target matches more than one pattern, all the -matching pattern-specific variables are interpreted in the order in -which they were defined in the makefile, and collected together into -one set. Variables defined in this way are searched after any -target-specific variables defined explicitly for that target, and -before target-specific variables defined for the parent target. +specified. Set a pattern-specific variable value like this: @@ -5748,6 +5743,31 @@ For example: will assign @code{CFLAGS} the value of @samp{-O} for all targets matching the pattern @code{%.o}. +If a target matches more than one pattern, the matching pattern-specific +variables with longer stems are interpreted first. This results in more +specific variables taking precedence over the more generic ones, for +example: + +@example +%.o: %.c + $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@@ + +lib/%.o: CFLAGS := -fPIC -g +%.o: CFLAGS := -g + +all: foo.o lib/bar.o +@end example + +In this example the first definition of the @code{CFLAGS} variable +will be used to update @file{lib/bar.o} even though the second one +also applies to this target. Pattern-specific variables which result +in the same stem length are considered in the order in which they +were defined in the makefile. + +Pattern-specific variables are searched after any target-specific +variables defined explicitly for that target, and before target-specific +variables defined for the parent target. + @node Suppressing Inheritance, Special Variables, Pattern-specific, Using Variables @section Suppressing Inheritance @findex private @@ -9143,11 +9163,28 @@ updated themselves. @cindex multiple targets, in pattern rule @cindex target, multiple in pattern rule -The order in which pattern rules appear in the makefile is important -since this is the order in which they are considered. -Of equally applicable -rules, only the first one found is used. The rules you write take precedence -over those that are built in. Note however, that a rule whose +It is possible that several pattern rules can be used to update a +target. In this case @code{make} considers rules which produce +shorter stems first. This results in more specific rules being +preferred to the more generic ones, for example: + +@example +%.o: %.c + $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@@ + +lib/%.o: lib/%.c + $(CC) -fPIC -c $(CFLAGS) $(CPPFLAGS) $< -o $@@ + +all: foo.o lib/bar.o +@end example + +In this example the second rule will be used to update @file{lib/bar.o} +even though the first rule can also be used. + +Pattern rules which result in the same stem length are considered in +the order in which they appear in the makefile. Of equally applicable +rules, only the first one found is used. The rules you write take +precedence over those that are built in. Note however, that a rule whose prerequisites actually exist or are mentioned always takes priority over a rule with prerequisites that must be made by chaining other implicit rules. @cindex pattern rules, order of |