Re: Having hard time adding to CFLAGS

[Josiah Worcester <josiahw@gmail.com>]

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On Thu, Oct 22, 2015 at 3:31 PM Denys Vlasenko <vda.linux@googlemail.com>
wrote:

> 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"
>
> It does work, but resulting libc.so is twice as big:
>    text       data        bss        dec        hex    filename
>  564099       1944      11768     577811      8d113    musl.1/lib/libc.so
>  917805       2130      11736     931671      e3757    musl.2/lib/libc.so
>
> The cause is that gcc invocation for each .c file in both cases start
> normally:
>
> gcc -std=c99 -nostdinc -ffreestanding -fexcess-precision=standard
> -frounding-math -D_XOPEN_SOURCE=700 -I./arch/x86_64 -I./src/internal
> -I./include...
>
> but then, build without explicit CFLAGS use this:
>
> ... -Os -pipe -fomit-frame-pointer -fno-unwind-tables
> -fno-asynchronous-unwind-tables -Wa,--noexecstack
> -Werror=implicit-function-declaration -Werror=implicit-int
> -Werror=pointer-sign -Werror=pointer-arith -include vis.h  -fPIC
> -DSHARED -c -o src/aio/aio.lo src/aio/aio.c
>
> and one with CFLAGS loses these flags, in particular, it has no -Os
> and no -fPIC:
>
> ... -falign-functions=1 -c -o src/aio/aio.o src/aio/aio.c
>
> 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.
>

This appears to be an issue with how you're expecting CFLAGS to work. As
with almost anything with configure, all the optimization flags you want
need to be in CFLAGS. Normally, a program would have nothing in there
otherwise, so you'd be just getting the "-falign-functions=1" flag going to
GCC. If you want to optimize it, you would actually need CFLAGS="-Os ...".

As for the "no -fPIC", I believe you're looking at the build for two
different objects. musl's build system builds both a static and shared
library, and the line you pasted there is the one that it uses for the
static library's objects. You could tell if it was intended to go into a
shared object because it would have a ".lo" suffix instead.

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