[v2] elf: Install a symbolic link to ld.so as /usr/bin/ld.so

  This makes ld.so features such as --preload, --audit,
and --list-diagnostics more accessible to end users because they
do not need to know the ABI name of the dynamic loader.

---
v2: Use $(make-link).
 NEWS         | 4 ++++
 elf/Makefile | 7 ++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)
  

* Florian Weimer via Libc-alpha:

> This makes ld.so features such as --preload, --audit,
> and --list-diagnostics more accessible to end users because they
> do not need to know the ABI name of the dynamic loader.
>
> ---
> v2: Use $(make-link).
>  NEWS         | 4 ++++
>  elf/Makefile | 7 ++++++-
>  2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/NEWS b/NEWS
> index f10971b180..2f56f3db28 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -68,6 +68,10 @@ Major new features:
>    to be used by compilers for optimizing usage of 'memcmp' when its
>    return value is only used for its boolean status.
>  
> +* A symbolic link to the dynamic linker is now installed under
> +  /usr/bin/ld.so (or ${bindir}/ld.so if glibc is not configured with
> +  --prefix=/usr).
> +
>  Deprecated and removed features, and other changes affecting compatibility:
>  
>  * The r_version update in the debugger interface makes the glibc binary
> diff --git a/elf/Makefile b/elf/Makefile
> index 72004484db..06cfde778c 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -110,7 +110,7 @@ endif
>  ifeq (yes,$(build-shared))
>  extra-objs	= $(all-rtld-routines:%=%.os) sofini.os interp.os
>  generated	+= librtld.os dl-allobjs.os ld.so ldd
> -install-others	= $(inst_rtlddir)/$(rtld-installed-name)
> +install-others	= $(inst_rtlddir)/$(rtld-installed-name) $(inst_bindir)/ld.so
>  install-bin-script = ldd
>  endif
>  
> @@ -682,6 +682,11 @@ $(inst_rtlddir)/$(rtld-installed-name): $(objpfx)ld.so $(+force)
>  	$(make-target-directory)
>  	$(do-install-program)
>  
> +# Creates the relative /usr/bin/ld.so symbolic link.
> +$(inst_bindir)/ld.so: $(inst_rtlddir)/$(rtld-installed-name)
> +	$(make-target-directory)
> +	$(make-link)
> +
>  # Special target called by parent to install just the dynamic linker.
>  .PHONY: ldso_install
>  ldso_install: $(inst_rtlddir)/$(rtld-installed-name)

Ping?  This patch needs review.  Do we want to make this change?

Thanks,
Florian
  

On Nov 15 2021, Florian Weimer via Libc-alpha wrote:

> This makes ld.so features such as --preload, --audit,
> and --list-diagnostics more accessible to end users because they
> do not need to know the ABI name of the dynamic loader.

Ok.

> diff --git a/NEWS b/NEWS
> index f10971b180..2f56f3db28 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -68,6 +68,10 @@ Major new features:
>    to be used by compilers for optimizing usage of 'memcmp' when its
>    return value is only used for its boolean status.
>  
> +* A symbolic link to the dynamic linker is now installed under
> +  /usr/bin/ld.so (or ${bindir}/ld.so if glibc is not configured with
> +  --prefix=/usr).

This is true even if --prefix=/usr.

Andreas.
  

* Andreas Schwab:

> On Nov 15 2021, Florian Weimer via Libc-alpha wrote:
>
>> This makes ld.so features such as --preload, --audit,
>> and --list-diagnostics more accessible to end users because they
>> do not need to know the ABI name of the dynamic loader.
>
> Ok.
>
>> diff --git a/NEWS b/NEWS
>> index f10971b180..2f56f3db28 100644
>> --- a/NEWS
>> +++ b/NEWS
>> @@ -68,6 +68,10 @@ Major new features:
>>    to be used by compilers for optimizing usage of 'memcmp' when its
>>    return value is only used for its boolean status.
>>  
>> +* A symbolic link to the dynamic linker is now installed under
>> +  /usr/bin/ld.so (or ${bindir}/ld.so if glibc is not configured with
>> +  --prefix=/usr).
>
> This is true even if --prefix=/usr.

I think there is value in mentioning the string /usr/bin/ld.so because
it's what users will say.  So perhaps this?

+* A symbolic link to the dynamic linker is now installed under
+  ${bindir}/ld.so (that is, /usr/bin/ld.so if glibc has been configured
+  with --prefix=/usr).

Do you have an opinion on adding the symbolic link?

Thanks,
Florian
  

On Nov 23 2021, Florian Weimer wrote:

> I think there is value in mentioning the string /usr/bin/ld.so because
> it's what users will say.  So perhaps this?

Perhaps use a similar wording as the previous occasion.

> Do you have an opinion on adding the symbolic link?

See above.

Andreas.
  

* Andreas Schwab:

> On Nov 23 2021, Florian Weimer wrote:
>
>> I think there is value in mentioning the string /usr/bin/ld.so because
>> it's what users will say.  So perhaps this?
>
> Perhaps use a similar wording as the previous occasion.
>
>> Do you have an opinion on adding the symbolic link?
>
> See above.

Sorry, I can't find the previous occasion you are referring to.  Would
you please provide an explicit pointer?

Thanks,
Florian
  

* Florian Weimer via Libc-alpha:

> This makes ld.so features such as --preload, --audit,
> and --list-diagnostics more accessible to end users because they
> do not need to know the ABI name of the dynamic loader.
>
> ---
> v2: Use $(make-link).
>  NEWS         | 4 ++++
>  elf/Makefile | 7 ++++++-
>  2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/NEWS b/NEWS
> index f10971b180..2f56f3db28 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -68,6 +68,10 @@ Major new features:
>    to be used by compilers for optimizing usage of 'memcmp' when its
>    return value is only used for its boolean status.
>  
> +* A symbolic link to the dynamic linker is now installed under
> +  /usr/bin/ld.so (or ${bindir}/ld.so if glibc is not configured with
> +  --prefix=/usr).

Some distribution discussions on this patch:

  /usr/bin/ld.so as a symbolic link for the dynamic loader

  <https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/SA244MNX5CC5OED65SX3QNCLKDUKW7D3/>

  <https://lists.debian.org/debian-glibc/2021/12/msg00001.html>
  <https://lists.debian.org/debian-devel/2021/12/msg00032.html>
  (thread wasn't Cc:ed to both lists throughout)

Based on the Debian feedback, I've fixed launching of statically linked
executables:

  [PATCH] elf: execve statically linked programs instead of crashing [BZ #28648]
  <https://sourceware.org/pipermail/libc-alpha/2021-December/133615.html>

Thanks,
Florian
  

On Sun, 5 Dec 2021 at 08:13, Florian Weimer via Libc-alpha <
libc-alpha@sourceware.org> wrote:

>
> Some distribution discussions on this patch:
>
>   /usr/bin/ld.so as a symbolic link for the dynamic loader
>
>   <
> https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/SA244MNX5CC5OED65SX3QNCLKDUKW7D3/
> >
>
>   <https://lists.debian.org/debian-glibc/2021/12/msg00001.html>
>   <https://lists.debian.org/debian-devel/2021/12/msg00032.html>
>   (thread wasn't Cc:ed to both lists throughout)


I think this is a good idea although I haven't thought incredibly hard
about it. I agree with Lennart that being able to readlink /usr/bin/ld.so
to get the default native dynamic linker path would be useful (although
there are probably other ways to meet that need).

Cheers,
mwh
  

See commit 141e4030d6:

+* The standard location for the file that says what the local timezone is
+  has changed again.  It is now `/usr/local/etc/localtime' (or more
+  precisely, `${prefix}/etc/localtime') rather than `/etc/localtime'.

Andreas.