[glibc/azanella/mseal] elf: Enable RTLD_NODELETE on __libc_unwind_link_get

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=3b8c02ca8b20b9ae1c0872426131402dc2b50695

commit 3b8c02ca8b20b9ae1c0872426131402dc2b50695
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Tue Jun 4 10:07:41 2024 -0300

    elf: Enable RTLD_NODELETE on __libc_unwind_link_get
    
    So the libgcc_s.so can also be sealed.  The library is loaded once
    and not unloaded during process execution (only for memory debug
    with __libc_unwind_link_freeres).

Diff:
---
 include/dlfcn.h    | 2 ++
 misc/unwind-link.c | 5 +++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/dlfcn.h b/include/dlfcn.h
index f49ee1b0c9..06e2ecbdd2 100644
--- a/include/dlfcn.h
+++ b/include/dlfcn.h
@@ -50,6 +50,8 @@ extern char **__libc_argv attribute_hidden;
    better error handling semantics for the library.  */
 #define __libc_dlopen(name) \
   __libc_dlopen_mode (name, RTLD_NOW | __RTLD_DLOPEN)
+#define __libc_dlopen_nodelete(name) \
+  __libc_dlopen_mode (name, RTLD_NODELETE | RTLD_NOW | __RTLD_DLOPEN)
 extern void *__libc_dlopen_mode  (const char *__name, int __mode)
   attribute_hidden;
 extern void *__libc_dlsym   (void *__map, const char *__name)
diff --git a/misc/unwind-link.c b/misc/unwind-link.c
index 213a0162a4..7267ecbec3 100644
--- a/misc/unwind-link.c
+++ b/misc/unwind-link.c
@@ -48,7 +48,7 @@ __libc_unwind_link_get (void)
   /* Initialize a copy of the data, so that we do not need about
      unlocking in case the dynamic loader somehow triggers
      unwinding.  */
-  void *local_libgcc_handle = __libc_dlopen (LIBGCC_S_SO);
+  void *local_libgcc_handle = __libc_dlopen_nodelete (LIBGCC_S_SO);
   if (local_libgcc_handle == NULL)
     {
       __libc_lock_unlock (lock);
@@ -100,7 +100,8 @@ __libc_unwind_link_get (void)
 
   __libc_lock_lock (lock);
   if (atomic_load_relaxed (&global_libgcc_handle) != NULL)
-    /* This thread lost the race.  Clean up.  */
+    /* This thread lost the race.  Drop the l_direct_opencount and issue
+       the debug log.  */
     __libc_dlclose (local_libgcc_handle);
   else
     {