Re: [PATCH] dlsym: Make RTLD_NEXT prefer default version definition [#BZ #14932]

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 20/05/2022 05:35, Fangrui Song via Libc-alpha wrote:
> When the first object providing foo defines both foo@v1 and foo@@v2,
> dlsym(RTLD_NEXT, "foo") returns foo@v1 while dlsym(RTLD_DEFAULT, "foo")
> returns foo@@v2.  The issue is that RTLD_DEFAULT use the
> DL_LOOKUP_RETURN_NEWEST flag while RTLD_NEXT doesn't.  Fix the RTLD_NEXT
> branch to use DL_LOOKUP_RETURN_NEWEST.

I am afraid we will need to add a compat dlsym for this change.

> ---
>  elf/Makefile       |  7 +++++++
>  elf/dl-sym.c       |  2 +-
>  elf/nextmod3.c     | 19 +++++++++++++++++++
>  elf/nextmod3.map   |  3 +++
>  elf/tst-next-ver.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 76 insertions(+), 1 deletion(-)
>  create mode 100644 elf/nextmod3.c
>  create mode 100644 elf/nextmod3.map
>  create mode 100644 elf/tst-next-ver.c
> 
> diff --git a/elf/Makefile b/elf/Makefile
> index 6f4ea78007..6cc0023364 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -425,6 +425,7 @@ tests += \
>    tst-initorder2 \
>    tst-latepthread \
>    tst-main1 \
> +  tst-next-ver \
>    tst-nodelete2 \
>    tst-nodelete-dlclose \
>    tst-nodelete-opened \
> @@ -711,6 +712,7 @@ modules-names += \
>    neededobj6 \
>    nextmod1 \
>    nextmod2 \
> +  nextmod3 \
>    nodel2mod1 \
>    nodel2mod2 \
>    nodel2mod3 \
> @@ -1689,6 +1691,9 @@ $(objpfx)reldep4.out: $(objpfx)reldep4mod1.so $(objpfx)reldep4mod2.so
>  $(objpfx)next: $(objpfx)nextmod1.so $(objpfx)nextmod2.so
>  LDFLAGS-next = -Wl,--no-as-needed
>  
> +$(objpfx)tst-next-ver: $(objpfx)nextmod3.so
> +LDFLAGS-tst-next-ver = -Wl,--no-as-needed
> +
>  $(objpfx)unload2.out: $(objpfx)unload2mod.so $(objpfx)unload2dep.so
>  
>  $(objpfx)lateglobal.out: $(objpfx)ltglobmod1.so $(objpfx)ltglobmod2.so
> @@ -2436,6 +2441,8 @@ $(objpfx)tst-linkall-static: \
>  endif
>  endif
>  
> +LDFLAGS-nextmod3.so = -Wl,--version-script=nextmod3.map
> +
>  # The application depends on the DSO, and the DSO loads the plugin.
>  # The plugin also depends on the DSO. This creates the circular
>  # dependency via dlopen that we're testing to make sure works.
> diff --git a/elf/dl-sym.c b/elf/dl-sym.c
> index aa993942df..b1cf42f36d 100644
> --- a/elf/dl-sym.c
> +++ b/elf/dl-sym.c
> @@ -144,7 +144,7 @@ RTLD_NEXT used in code not dynamically loaded"));
>  	l = l->l_loader;
>  
>        result = GLRO(dl_lookup_symbol_x) (name, match, &ref, l->l_local_scope,
> -					 vers, 0, 0, match);
> +					 vers, 0, flags, match);
>      }
>    else
>      {
> diff --git a/elf/nextmod3.c b/elf/nextmod3.c
> new file mode 100644
> index 0000000000..96608a65c0
> --- /dev/null
> +++ b/elf/nextmod3.c
> @@ -0,0 +1,19 @@
> +int
> +foo_v1 (int a)
> +{
> +  return 1;
> +}
> +asm (".symver foo_v1, foo@v1");
> +
> +int
> +foo_v2 (int a)
> +{
> +  return 2;
> +}
> +asm (".symver foo_v2, foo@v2");
> +
> +int
> +foo (int a)
> +{
> +  return 3;
> +}
> diff --git a/elf/nextmod3.map b/elf/nextmod3.map
> new file mode 100644
> index 0000000000..0a8e4e4ee3
> --- /dev/null
> +++ b/elf/nextmod3.map
> @@ -0,0 +1,3 @@
> +v1 { };
> +v2 { };
> +v3 { foo; };
> diff --git a/elf/tst-next-ver.c b/elf/tst-next-ver.c
> new file mode 100644
> index 0000000000..7241f9038b
> --- /dev/null
> +++ b/elf/tst-next-ver.c
> @@ -0,0 +1,46 @@
> +/* Test RTLD_DEFAULT/RTLD_NEXT when the definition has multiple versions.
> +   Copyright (C) 2018-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <dlfcn.h>
> +#include <stdio.h>
> +
> +#include "testobj.h"
> +
> +static int
> +do_test (void)
> +{
> +  /* Resolve to foo@@v3 in nextmod3.so, instead of
> +     foo@v1 or foo@v2.  */
> +  int (*fp) (int) = dlsym (RTLD_DEFAULT, "foo");
> +  int res = fp (0);
> +  printf ("preload (0) = %d, %s\n", res, res == 3 ? "ok" : "wrong");
> +  if (res != 3)
> +    return 1;
> +
> +  /* Resolve to foo@@v3 in nextmod3.so, instead of
> +     foo@v1 or foo@v2.  */
> +  fp = dlsym (RTLD_NEXT, "foo");
> +  res = fp (0);
> +  printf ("preload (0) = %d, %s\n", res, res == 3 ? "ok" : "wrong");
> +  if (res != 3)
> +    return 1;
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>