A certain makefile (namely, the otherlibs/num/Makefile in the OCaml 4.2 distribution) has the following line :
EXTRACFLAGS=-DBNG_ARCH_$(BNG_ARCH) -DBNG_ASM_LEVEL=$(BNG_ASM_LEVEL)
I am surprised to see two assignments on the same line here. What does it mean ? Is it the same as
EXTRACFLAGS=-DBNG_ARCH_$(BNG_ARCH)
-DBNG_ASM_LEVEL=$(BNG_ASM_LEVEL)
I did not find anything about that in the GNU make manual, maybe I am unaware of the right keyword to search this.
There are not two assignments here. The line assigns the definition:
-DBNG_ARCH_$(BNG_ARCH) -DBNG_ASM_LEVEL=$(BNG_ASM_LEVEL)
to the make variable EXTRACFLAGS. The value appears to consist
of flags that are to be passed to some invocation of the C preprocessor to
define macros BNG_ARCH_$(BNG_ARCH) and BNG_ASM_LEVEL. E.g. as
in a make recipe:
$(CPP) $(EXTRACFLAGS) ...
Which, supposing the make assignments:
BNG_ARCH = foo
BNG_ASM_LEVEL = bar
would expand to:
cpp -DBNG_ARCH_foo -DBNG_ASM_LEVEL=bar ...
OP comments:
So you might say that = is "left-associative", the leftmost = sign is the one that really gets executed. Is this documented somewhere in the manual?
From my frequent, but far from exhaustive resorts to manual I can't say it is documented. Somebody
may know better. There is no formal grammar there, but it is everywhere illustrated that the definition of a variable extends from the
start of the non-whitespace text following =, := or ?= to the end of the (possibly \-extended)
logical line. You may satisfied on the point by running the makefile:
.PHONY: all
x = X y = Y
all:
@echo [$(x)]
@echo [$(y)]
which prints:
[X y = Y]
[]
Assignment signs within a make-definition are not assignments, they're just characters in the definition.