Some questions about use libtool when linking

[Kun Yang]

Greetings,

I'm intended to update libtool package for MSYS2, but some troubles occurred

that beyond my ability. I'm confused by some flags when linking.

Compared to v2.4.7, libtool now accepts more flags when linking. The most of the

flags in

https://github.com/msys2/MSYS2-packages/blob/master/libtool/0003-Pass-various-runtime-library-flags-to-GCC.mingw.patch

were added in v2.5.3. As you can see, there is still some flags automatically

ignored by libtool when linking. For example, you can run the following commands

in your shell.

libtool --version | head -1

echo "void foo(void) {}" >foo.c

libtool --mode=compile --tag=CC cc -c foo.c -o foo.lo -O3 -ffast-math

libtool --mode=link --tag=CC cc foo.lo -o libfoo.la -O3 -ffast-math -rpath

/usr/lib -version-info 0 -no-undefined

Here is the output on Arch Linux with libtool v2.5.3 (they prefer uses git

instead of the unstable version, so -dirty were append in the version string)

libtool (GNU libtool) 2.5.3-dirty

libtool: compile: cc -c foo.c -O3 -ffast-math -fPIC -DPIC -o .libs/foo.o

libtool: compile: cc -c foo.c -O3 -ffast-math -o foo.o >/dev/null 2>&1

libtool: link: rm -fr .libs/libfoo.a .libs/libfoo.la .libs/libfoo.lai

.libs/libfoo.so .libs/libfoo.so.0 .libs/libfoo.so.0.0.0 libtool: link: gcc

-shared -fPIC -DPIC .libs/foo.o -O3 -Wl,-soname -Wl,libfoo.so.0 -o

.libs/libfoo.so.0.0.0 libtool: link: (cd ".libs" && rm -f "libfoo.so.0" && ln -s

"libfoo.so.0.0.0" "libfoo.so.0") libtool: link: (cd ".libs" && rm -f "libfoo.so"

&& ln -s "libfoo.so.0.0.0" "libfoo.so") libtool: link: ar cr .libs/libfoo.a

foo.o libtool: link: ranlib .libs/libfoo.a libtool: link: ( cd ".libs" && rm -f

"libfoo.la" && ln -s "../libfoo.la" "libfoo.la" )

As what you saw, -ffast-math were ignored. However, I found that some flags were

necessary on some platforms to generate startup code for these flags. See the

footnote in the following page.

https://gcc.gnu.org/onlinedocs/gcc/Link-Options.html#FOOT1

Is there any reason why these flags not included? Is it necessary for linking?

If so, could anyone please give me a full list of these flags which are probably

necessary for linking?

I would really appreciate it if you could give me a hand.

Best Regards,

Yang Kun