David Haller <gen...@dhaller.de> [16-10-02 06:16]:
> Hello,
>
> On Sun, 02 Oct 2016, meino.cra...@gmx.de wrote:
> >Suppose I would compile a program, which uses shared libraries and I
> >specify an additional library, which will be completly unused by the
> >code...will the resulting executable differ from an executable which
> >is compiled without this library ?
>
> Suppose you'd just test it?
>
> $ echo 'int main(void) {return 0;}' > t.c
> $ gcc -o t_nolib t.c
> $ gcc -o t_lib -lglib t.c
> $ gcc -o t_lib_as -Wl,-as-needed -lglib t.c
> $ gcc -o t_lib_nas -Wl,-no-as-needed -lglib t.c
> $ cmp t_nolib t_lib_as; echo $?
> 0
>
>
> $ ls -l
> -rw-r----- 1 dh dh 27 Oct 2 05:40 t.c
> -rwxr-x--- 1 dh dh 6824 Oct 2 05:40 t_lib
> -rwxr-x--- 1 dh dh 6424 Oct 2 05:40 t_lib_as
> -rwxr-x--- 1 dh dh 6824 Oct 2 05:40 t_lib_nas
> -rwxr-x--- 1 dh dh 6424 Oct 2 05:40 t_nolib
>
> $ ldd t_*
> t_lib:
> linux-vdso.so.1 (0x00007fff0b7ff000)
> libglib-1.2.so.0 => /usr/lib64/libglib-1.2.so.0 (0x00007f372b55b000)
> libc.so.6 => /lib64/libc.so.6 (0x00007f372b1bb000)
> libdl.so.2 => /lib64/libdl.so.2 (0x00007f372afb7000)
> /lib64/ld-linux-x86-64.so.2 (0x00007f372b793000)
> t_lib_as:
> linux-vdso.so.1 (0x00007fffadf70000)
> libc.so.6 => /lib64/libc.so.6 (0x00007ff9289d7000)
> /lib64/ld-linux-x86-64.so.2 (0x00007ff928d77000)
> t_lib_nas:
> linux-vdso.so.1 (0x00007fffe9e6f000)
> libglib-1.2.so.0 => /usr/lib64/libglib-1.2.so.0 (0x00007f2a43afb000)
> libc.so.6 => /lib64/libc.so.6 (0x00007f2a4375b000)
> libdl.so.2 => /lib64/libdl.so.2 (0x00007f2a43557000)
> /lib64/ld-linux-x86-64.so.2 (0x00007f2a43d33000)
> t_nolib:
> linux-vdso.so.1 (0x00007fffbed58000)
> libc.so.6 => /lib64/libc.so.6 (0x00007fe55b4f4000)
> /lib64/ld-linux-x86-64.so.2 (0x00007fe55b894000)
>
> So: YES, it will differ unless you use the "-as-needed" ld flag. Which
> is why some distros have -as-needed as a default linker flag, to prune
> deps of packages, even though it causes "trouble" at times ...
>
> -dnh
>
> --
> Graphisch??? Wie meinen? Hast du zuviel Fleisch von zu "gluecklichen"
> Rindern gefuttert? *scnr* Wozu zum Henker sollte man sowas brauchen?
> Logo ginge auch per ASCII :) (Logo? welches Logo? Wozu ueberhaupt?)
> [David Haller in suse-linux]
>
Hi David, Hi Michael,
thanks a LOT for your heavy testing!!!
I didn't thought, that the answers are THAT various...
I only thought of one answer at all... X)
One curious question remains:
If -as-needed is included, all libs will be "delinked" :), which
are not used...so I am throwing away stuff, which no code calls:
WHY should this cause trouble?
Or is it again oversimplified by me? :) ;) 8)
Cheers,
Meino
