Re: [lmi] [lmi-commits] master e4abb6e1 14/17: Don't specify nonempty $CFLAGS or $CXXFLAGS

[Vadim Zeitlin]

On Tue, 5 Jul 2022 10:11:27 +0000 Greg Chicares <gchicares@sbcglobal.net> wrote:

GC> Let's try a concrete example, taking care to follow this advice:

 Sorry, I'm not sure I follow: what does this example test/prove exactly?

GC> https://www.gnu.org/software/make/manual/make.html#Overriding
GC> | The makefile probably specifies the usual value for CFLAGS, like this:
GC> | CFLAGS=-g
GC> 
GC> This makefile's author successfully forces "-fno-omit-frame-pointer",
GC> but less successfully hopes also to specify a default flag '-g' that
GC> is intended to persist when the user overrides $CFLAGS using "+=".

 But it doesn't use += for CFLAGS?

GC> $ cat eraseme.make
GC> CFLAGS=-g
GC> ALL_CFLAGS = -std=c99 $(CFLAGS) -fno-omit-frame-pointer
GC> 
GC> %.o: %.c
GC>         $(CC) $(ALL_CFLAGS) $< -o$@
GC> 
GC> test_flags:
GC>         @echo "CFLAGS is $(CFLAGS)"
GC>         @echo "ALL_CFLAGS is $(ALL_CFLAGS)"
GC> 
GC> With no command-line override, '-g' is used, of course:
GC> 
GC> $ make -f eraseme.make test_flags
GC> CFLAGS is -g
GC> ALL_CFLAGS is -std=c99 -g -fno-omit-frame-pointer
GC> 
GC> With a command-line override, '-g' vanishes:
GC> 
GC> $ make CFLAGS+="-O3 -fomit-frame-pointer" -f eraseme.make test_flags
GC> CFLAGS is -O3 -fomit-frame-pointer
GC> ALL_CFLAGS is -std=c99 -O3 -fomit-frame-pointer -fno-omit-frame-pointer
GC> 
GC> Writing "=" instead of "+=" produces the same outcome:
GC> 
GC> $ make CFLAGS="-O3 -fomit-frame-pointer" -f eraseme.make test_flags
GC> CFLAGS is -O3 -fomit-frame-pointer
GC> ALL_CFLAGS is -std=c99 -O3 -fomit-frame-pointer -fno-omit-frame-pointer

 But nobody writes "+=" on the command line, as it's mostly useless because
there is no value to append to. Well, I guess you could do something like

        $ CFLAGS=-fxxx make CFLAGS+=-fyyy ...

but, again, this is something I have literally never seen.

 The idea would rather be to write "CFLAGS += -g" in the makefile itself,
wouldn't it?

 Sorry again if I'm completely missing the point here, as I have a
suspicion I might be...

VZ

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