Re: Having hard time adding to CFLAGS

[Rich Felker <dalias@libc.org>]

On Fri, Oct 23, 2015 at 01:23:30AM +0200, Szabolcs Nagy wrote:
> * Denys Vlasenko <vda.linux@googlemail.com> [2015-10-23 00:31:09 +0200]:
> > Let's say I need to add a gcc option to my musl build.
> > 
> > configure says:
> > ...
> > Some influential environment variables:
> >   CC                      C compiler command [detected]
> >   CFLAGS                  C compiler flags [-Os -pipe ...]
> >   CROSS_COMPILE           prefix for cross compiler and tools [none]
> >   LIBCC                   compiler runtime library [detected
> > 
> > So I try this, combining all possible ways of passing CFLAGS
> > (past experience is that different projects do it differently).
> > 
> > CFLAGS is in environment, and on both configure and make
> > command lines:
> > 
> > export CFLAGS="-falign-functions=1"    # for example
> > ./configure CFLAGS="$CFLAGS"
> > make CFLAGS="$CFLAGS"
> 
> this is not what configure said...
> 
> > Evidently, my CFLAGS replaced needed flags instead of being added at the end.
> > 
> > Can this be fixed? If user needs to use e.g. EXTRA_CFLAGS instead,
> > please fix configure --help.
> 
> it can be fixed, but i think 'needed flag' is not
> always clear and overriding CFLAGS on the make
> commandline is not polite.

Agreed. If you pass CFLAGS to configure, there's no reason to override
it later. But it also shouldn't break.

> the attached patch makes this work, but i
> consider -Os to be not part of 'needed'

> diff --git a/Makefile b/Makefile
> index 844a017..f713286 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -94,22 +94,22 @@ crt/crt1.o crt/Scrt1.o crt/rcrt1.o src/ldso/dlstart.lo: $(wildcard arch/$(ARCH)/
>  
>  crt/rcrt1.o: src/ldso/dlstart.c
>  
> -crt/Scrt1.o crt/rcrt1.o: CFLAGS += -fPIC
> +crt/Scrt1.o crt/rcrt1.o: CFLAGS_ALL += -fPIC

This is the correct fix. I was not aware that make variables set from
the make command line would take precedence over the target-specific
+= concatenations. The intent has always been that editing CFLAGS
should not break the build (unless you put really inapproriate stuff
there, of course).

Rich