Re: Some questions about use libtool when linking

Ileana Dumitrescu <[email protected]> Mon, 21 Oct 2024 18:48:09 +0300
Newsgroups	gmane.comp.gnu.libtool.general
Message-ID	<[email protected]>
On 08/10/2024 18:31, Kun Yang wrote:
> 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?

Flags are added here to pass through at link time instead of being
stripped, so if '-ffastmath' is necessary for linking, it can be added
with a comment above to provide reasoning.

> Is it necessary for linking?

-ffast-math is an optimization option. I assume it is not necessary for
linking, but I may be wrong.

> If so, could anyone please give me a full list of these flags which are 
> probably necessary for linking?

If the options listed here [1] are needed, I would be happy to accept a
patch for them with the listed rationale for why these flags should be
passed through unchanged.

[1] 
https://github.com/msys2/MSYS2-packages/blob/master/libtool/0003-Pass-various-runtime-library-flags-to-GCC.mingw.patch

-- 
Ileana Dumitrescu

GPG Public Key: FA26 CA78 4BE1 8892 7F22 B99F 6570 EA01 146F 7354
OpenPGP_0x6570EA01146F7354.asc (application/pgp-keys, 6.3 KB)
OpenPGP_signature.asc (application/pgp-signature, 840 B)