Is --as-needed the default these days?

Is --as-needed the default these days?

[Yuri Kanivetsky]

Hi,

It looks like somewhere between gcc-5.3.0 and gcc-6.2.1 --as-needed
became the default:

https://gist.github.com/x-yuri/1b4c19891be50b2b8801689de1487009

In other words it looks like on Alpine Linux 3.4 -lintl always adds
libintl, on >= 3.5 only if some of its symbols are really needed.

Can you possibly give a link to the commit or a changelog entry?

Regards,
Yuri

Re: Is --as-needed the default these days?

[Jonathan Wakely]

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On Sun, 24 Mar 2024, 18:01 Yuri Kanivetsky via Gcc, <gcc@gcc.gnu.org> wrote:

> Hi,
>
> It looks like somewhere between gcc-5.3.0 and gcc-6.2.1 --as-needed
> became the default:
>
> https://gist.github.com/x-yuri/1b4c19891be50b2b8801689de1487009
>
> In other words it looks like on Alpine Linux 3.4 -lintl always adds
> libintl, on >= 3.5 only if some of its symbols are really needed.
>
> Can you possibly give a link to the commit or a changelog entry?
>

That's a linker option, and the linker is not part of GCC. Any change in
linker behaviour is not because of a change in GCC.

The GNU linker can be configured to default to --as-needed or not, and
different distros use different defaults.

Re: Is --as-needed the default these days?

[Yuri Kanivetsky]

> That's a linker option, and the linker is not part of GCC. Any change in linker behaviour is not because of a change in GCC.

Have you noticed what gcc does?

3.4: /usr/libexec/gcc/x86_64-alpine-linux-musl/5.3.0/collect2 ... -lintl
3.5: /usr/libexec/gcc/x86_64-alpine-linux-musl/6.2.1/collect2 ...
--as-needed ... -lintl

collect2 is supposedly part of GCC. And what passes --as-needed is
supposedly gcc.

I was told on IRC that generally --as-needed is not the default. For
the linker I guess. Although I wasn't able to confirm it. The option
is supposedly defined here:

https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/lexsup.c;h=dad3b6059edfe1fe31f46c454fdc90d55b0aed5b;hb=ec6f962151998434f9cc743386f2a49a1ce1a0f6#l295

But I don't see the default value, and where it's used.

And also it looks like gcc started to pass --as-needed to the linker
since 5.x/6.x.

Am I missing something?

> The GNU linker can be configured to default to --as-needed or not, and different distros use different defaults.

Can you tell me briefly how it's configured? Is there a config?

Regards,
Yuri

Re: Is --as-needed the default these days?

[Andrew Pinski]

On Sun, Mar 24, 2024 at 11:54 AM Yuri Kanivetsky via Gcc
<gcc@gcc.gnu.org> wrote:
>
> > That's a linker option, and the linker is not part of GCC. Any change in linker behaviour is not because of a change in GCC.
>
> Have you noticed what gcc does?
Upstream GCC does (still) not default to adding `--as-needed` to the
command line (except around libgcc). Some distros add patches which
add `--as-needed` by default though. It looks like alpine is one of
those distros. Maybe you should ask them instead of asking us. It
looks like they made the change between their 3.4 and 3.5 release.

Thanks,
Andrew Pinski

>
> 3.4: /usr/libexec/gcc/x86_64-alpine-linux-musl/5.3.0/collect2 ... -lintl
> 3.5: /usr/libexec/gcc/x86_64-alpine-linux-musl/6.2.1/collect2 ...
> --as-needed ... -lintl
>
> collect2 is supposedly part of GCC. And what passes --as-needed is
> supposedly gcc.
>
> I was told on IRC that generally --as-needed is not the default. For
> the linker I guess. Although I wasn't able to confirm it. The option
> is supposedly defined here:
>
> https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/lexsup.c;h=dad3b6059edfe1fe31f46c454fdc90d55b0aed5b;hb=ec6f962151998434f9cc743386f2a49a1ce1a0f6#l295
>
> But I don't see the default value, and where it's used.
>
> And also it looks like gcc started to pass --as-needed to the linker
> since 5.x/6.x.
>
> Am I missing something?
>
> > The GNU linker can be configured to default to --as-needed or not, and different distros use different defaults.
>
> Can you tell me briefly how it's configured? Is there a config?
>
> Regards,
> Yuri

Re: Is --as-needed the default these days?

[Yuri Kanivetsky]

> Upstream GCC does (still) not default to adding `--as-needed` to the
> command line (except around libgcc). Some distros add patches which
> add `--as-needed` by default though. It looks like alpine is one of
> those distros. Maybe you should ask them instead of asking us. It
> looks like they made the change between their 3.4 and 3.5 release.

I believe I've found the change:

https://git.alpinelinux.org/aports/commit/?id=5b7befa1b989315a57f4fb49b8381ce06ded96c9

As we saw above on 3.4 (gcc-5.3.0) it adds libintl, on 3.5 (gcc-6.2.1)
it doesn't.

This commit changes pkgver from 5.3.0 to 6.1.0 and seems to make gcc
add --as-needed, can you confirm?

> Thanks,
> Andrew Pinski
>
> >
> > 3.4: /usr/libexec/gcc/x86_64-alpine-linux-musl/5.3.0/collect2 ... -lintl
> > 3.5: /usr/libexec/gcc/x86_64-alpine-linux-musl/6.2.1/collect2 ...
> > --as-needed ... -lintl
> >
> > collect2 is supposedly part of GCC. And what passes --as-needed is
> > supposedly gcc.
> >
> > I was told on IRC that generally --as-needed is not the default. For
> > the linker I guess. Although I wasn't able to confirm it. The option
> > is supposedly defined here:
> >
> > https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/lexsup.c;h=dad3b6059edfe1fe31f46c454fdc90d55b0aed5b;hb=ec6f962151998434f9cc743386f2a49a1ce1a0f6#l295
> >
> > But I don't see the default value, and where it's used.
> >
> > And also it looks like gcc started to pass --as-needed to the linker
> > since 5.x/6.x.
> >
> > Am I missing something?
> >
> > > The GNU linker can be configured to default to --as-needed or not, and different distros use different defaults.
> >
> > Can you tell me briefly how it's configured? Is there a config?
> >
> > Regards,
> > Yuri