elf(5) and ld.so(8): DT_RPATH deprecated - really?

elf(5) and ld.so(8): DT_RPATH deprecated - really?

[Joachim Wuttke]

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Pages elf(5) and ld.so(8) say that DT_RPATH is deprecated.

This is inconsistent with ld(1), which does not warn that
--disable-new-dtags is deprecated.

And it is not credible. A huge amount of software would
break down if support for DT_RPATH were ever removed.

Regards, Joachim

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Re: elf(5) and ld.so(8): DT_RPATH deprecated - really?

[Alejandro Colomar]

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Hi Joachim,

On Fri, Apr 19, 2024 at 08:43:33AM +0200, Joachim Wuttke wrote:
> Pages elf(5) and ld.so(8) say that DT_RPATH is deprecated.

The blames are:

commit 28d979c8c7fbdca65e221eca4e21823735f5db8d
Author: Michael Kerrisk <mtk.manpages@gmail.com>
Date:   Fri Jul 15 12:06:06 2005 +0000

    Mike Frysinger <vapier@gentoo.org>
    tweaked the short description to include definition of 'ELF'
    add ELFOSABI_NONE to the ELFOSABI_ list
    tweak/add more machines to EM_ list for ehdr->e_machine
    fix indenting to be consistent
    tweak the display of the ELF_ST_* macros
    document the Elf_Dyn structure

and

commit 121edebe2e0b36c3cfc306fbf88bfb6d17993b63
Author: Krónos <Krónos@Sāturnus>
Date:   Sun Dec 23 23:36:00 2001 +0100

    man-pages 1.46
    
    Link: <https://www.win.tue.nl/~aeb/ftpdocs/linux-local/manpages.archive/>
    Signed-off-by: Alejandro Colomar <alx@kernel.org>


I also found a few pages talking about it being deprecated:

<https://stackoverflow.com/questions/67131565/how-do-i-set-dt-rpath-or-dt-runpath>
<https://stackoverflow.com/questions/7967848/use-rpath-but-not-runpath>

> This is inconsistent with ld(1), which does not warn that
> --disable-new-dtags is deprecated.

I've added bug-binutils@ to the thread, in case they want to update
their manual to add a deprecation notice.

> And it is not credible. A huge amount of software would
> break down if support for DT_RPATH were ever removed.

Nobody said it would be removed soon.  But it seems people want to
remove it "eventually", with that eventually possibly being in a couple
of centuries, if computers still exist.

But if you have the intention of using it in new software, or keeping it
in existing software, maybe you could give your reasons to those who
deprecated it, so that either you convince them of its usefulness, or
they convince you of not using it.

Have a locely day!
Alex

> Regards, Joachim

-- 
<https://www.alejandro-colomar.es/>

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Re: elf(5) and ld.so(8): DT_RPATH deprecated - really?

[Joseph Myers]

On Mon, 22 Apr 2024, Alejandro Colomar wrote:

> Nobody said it would be removed soon.  But it seems people want to
> remove it "eventually", with that eventually possibly being in a couple
> of centuries, if computers still exist.
> 
> But if you have the intention of using it in new software, or keeping it
> in existing software, maybe you could give your reasons to those who
> deprecated it, so that either you convince them of its usefulness, or
> they convince you of not using it.

DT_RPATH is just as useful as it always was for testing purposes, when 
you're building binaries against a sysroot and use -rpath and 
-dynamic-linker pointing to that sysroot, and you really do want the RPATH 
used at runtime to find both direct and indirect dependencies and 
DT_RUNPATH would *not* serve the same purpose (because the sysroot is 
intended to have exactly the same binaries that would eventually be used 
in the root filesystem of the target in production, it would not be 
appropriate to set DT_RUNPATH in any of those binaries).

-- 
Joseph S. Myers
josmyers@redhat.com

Re: elf(5) and ld.so(8): DT_RPATH deprecated - really?

[Alejandro Colomar]

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On Mon, Apr 22, 2024 at 04:22:13PM +0000, Joseph Myers wrote:
> On Mon, 22 Apr 2024, Alejandro Colomar wrote:
> 
> > Nobody said it would be removed soon.  But it seems people want to
> > remove it "eventually", with that eventually possibly being in a couple
> > of centuries, if computers still exist.
> > 
> > But if you have the intention of using it in new software, or keeping it
> > in existing software, maybe you could give your reasons to those who
> > deprecated it, so that either you convince them of its usefulness, or
> > they convince you of not using it.
> 
> DT_RPATH is just as useful as it always was for testing purposes, when 
> you're building binaries against a sysroot and use -rpath and 
> -dynamic-linker pointing to that sysroot, and you really do want the RPATH 
> used at runtime to find both direct and indirect dependencies and 
> DT_RUNPATH would *not* serve the same purpose (because the sysroot is 
> intended to have exactly the same binaries that would eventually be used 
> in the root filesystem of the target in production, it would not be 
> appropriate to set DT_RUNPATH in any of those binaries).

Hi Joseph!

Then I guess we must undeprecate it.  I'm fine with that, as long as the
maintainers of ld(1) agree.  Joachim, would you mind sending a patch,
and CC binutils?  I'll leave it a week or two to gather reviews, and if
nobody opposes, I'll merge it.  I can also prepare the patch, if you
prefer.

Have a lovely day!
Alex

> 
> -- 
> Joseph S. Myers
> josmyers@redhat.com
> 

-- 
<https://www.alejandro-colomar.es/>

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Re: elf(5) and ld.so(8): DT_RPATH deprecated - really?

[Joachim Wuttke]

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Hi Alex and all:

 > But it seems people want to remove it "eventually" ...
 > in a couple of centuries ...

Deprecation, in my understanding, requires a realistic
roadmap for change, and in particular there must be
a way to replace any legitimate use of the old facility
by a functionally equivalent new construct.

 > if you have the intention of using it in new software,
 > or keeping it in existing software, maybe you could
 > give your reasons

In addition to what Joseph wrote:

 > ... useful as it always was for testing purposes ...

We are using RPATH not only in testing, but also in
deployment, namely in binary installers where we
bundle our application's binary executable with
all direct and indirect shared library dependencies,
except the most basic system libraries.

 > would you mind sending a patch, and CC binutils

I'll try tomorrow.

Kind greetings, Joachim


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[patch] elf.5 and ld.so.8: undeprecate DT_RPATH; explain DT_RPATH vs DT_RUNPATH

[Joachim Wuttke]

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In elf.5 and ld.so.8, remove deprecation of DT_RPATH
In elf.5, amend the description of DT_RUNPATH and DT_RPATH.

Rationale:
There is no credible path towards removal of DT_RPATH.
Lots of software depend on DT_RPATH as is.
It is used e.g. for testing and in binary installers.

Signed-off-by: Joachim Wuttke <j.wuttke@fz-juelich.de>
---
  man5/elf.5   | 4 ++--
  man8/ld.so.8 | 1 -
  2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/man5/elf.5 b/man5/elf.5
index 9aff88afb..57136159c 100644
--- a/man5/elf.5
+++ b/man5/elf.5
@@ -1787,7 +1787,7 @@ Address of the termination function
  String table offset to name of shared object
  .TP
  .B DT_RPATH
-String table offset to library search path (deprecated)
+String table offset to search path for direct and indirect library dependencies
  .TP
  .B DT_SYMBOLIC
  Alert linker to search this shared object before the executable for symbols
@@ -1819,7 +1819,7 @@ Instruct dynamic linker to process all relocations before
  transferring control to the executable
  .TP
  .B DT_RUNPATH
-String table offset to library search path
+String table offset to search path for direct library dependencies
  .TP
  .B DT_LOPROC
  .TQ
diff --git a/man8/ld.so.8 b/man8/ld.so.8
index fa75b7820..23cddb9df 100644
--- a/man8/ld.so.8
+++ b/man8/ld.so.8
@@ -61,7 +61,6 @@ then it is searched for in the following order:
  Using the directories specified in the
  DT_RPATH dynamic section attribute
  of the binary if present and DT_RUNPATH attribute does not exist.
-Use of DT_RPATH is deprecated.
  .IP (2)
  Using the environment variable
  .BR LD_LIBRARY_PATH ,
-- 
2.43.0


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Re: [patch] elf.5 and ld.so.8: undeprecate DT_RPATH; explain DT_RPATH vs DT_RUNPATH

[Alejandro Colomar]

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Hi Joachim,

On Tue, Apr 23, 2024 at 09:53:03AM +0200, Joachim Wuttke wrote:
> In elf.5 and ld.so.8, remove deprecation of DT_RPATH
> In elf.5, amend the description of DT_RUNPATH and DT_RPATH.
> 
> Rationale:
> There is no credible path towards removal of DT_RPATH.
> Lots of software depend on DT_RPATH as is.
> It is used e.g. for testing and in binary installers.
> 
> Signed-off-by: Joachim Wuttke <j.wuttke@fz-juelich.de>

Patch applied.  Thanks!
<https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=5fe3738ffceec44fac809fd1acfd65e74b84ff93>

Have a lovely day!
Alex

> ---
>  man5/elf.5   | 4 ++--
>  man8/ld.so.8 | 1 -
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/man5/elf.5 b/man5/elf.5
> index 9aff88afb..57136159c 100644
> --- a/man5/elf.5
> +++ b/man5/elf.5
> @@ -1787,7 +1787,7 @@ Address of the termination function
>  String table offset to name of shared object
>  .TP
>  .B DT_RPATH
> -String table offset to library search path (deprecated)
> +String table offset to search path for direct and indirect library dependencies
>  .TP
>  .B DT_SYMBOLIC
>  Alert linker to search this shared object before the executable for symbols
> @@ -1819,7 +1819,7 @@ Instruct dynamic linker to process all relocations before
>  transferring control to the executable
>  .TP
>  .B DT_RUNPATH
> -String table offset to library search path
> +String table offset to search path for direct library dependencies
>  .TP
>  .B DT_LOPROC
>  .TQ
> diff --git a/man8/ld.so.8 b/man8/ld.so.8
> index fa75b7820..23cddb9df 100644
> --- a/man8/ld.so.8
> +++ b/man8/ld.so.8
> @@ -61,7 +61,6 @@ then it is searched for in the following order:
>  Using the directories specified in the
>  DT_RPATH dynamic section attribute
>  of the binary if present and DT_RUNPATH attribute does not exist.
> -Use of DT_RPATH is deprecated.
>  .IP (2)
>  Using the environment variable
>  .BR LD_LIBRARY_PATH ,
> -- 
> 2.43.0
> 

-- 
<https://www.alejandro-colomar.es/>
A client is hiring kernel driver, mm, and/or crypto developers;
contact me if interested.

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