From FEDORA_PATCHES Mon Sep 17 00:00:00 2001

From: Kevin Buettner <kevinb@redhat.com>

Date: Wed, 9 Jun 2021 18:07:45 -0700

Subject: gdb-rhbz1971095-libthread_db-update-2of5.patch

;; Backport "libthread_db initialization changes related to upcoming

;; glibc-2.34"

;; (Kevin Buettner, RH BZ 19710950

This commit makes some adjustments to accomodate the upcoming

glibc-2.34 release.  Beginning with glibc-2.34, functionality formerly

contained in libpthread has been moved to libc.  For the time being,

libpthread.so still exists in the file system, but it won't show up in

ldd output and therefore won't be able to trigger initialization of

libthread_db related code.  E.g...

Fedora 34 / glibc-2.33.9000:

[kev@f34-2 gdb]$ ldd testsuite/outputs/gdb.threads/tls/tls

	linux-vdso.so.1 (0x00007ffcf94fa000)

	libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007ff0ba9af000)

	libm.so.6 => /lib64/libm.so.6 (0x00007ff0ba8d4000)

	libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007ff0ba8b9000)

	libc.so.6 => /lib64/libc.so.6 (0x00007ff0ba6c6000)

	/lib64/ld-linux-x86-64.so.2 (0x00007ff0babf0000)

Fedora 34 / glibc-2.33:

[kev@f34-1 gdb]$ ldd testsuite/outputs/gdb.threads/tls/tls

	linux-vdso.so.1 (0x00007fff32dc0000)

	libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f815f6de000)

	libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f815f4bf000)

	libm.so.6 => /lib64/libm.so.6 (0x00007f815f37b000)

	libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f815f360000)

	libc.so.6 => /lib64/libc.so.6 (0x00007f815f191000)

	/lib64/ld-linux-x86-64.so.2 (0x00007f815f721000)

Note that libpthread is missing from the ldd output for the

glibc-2.33.9000 machine.

This means that (unless we happen to think of some entirely different

mechanism), we'll now need to potentially match "libc" in addition to

"libpthread" as libraries which might be thread libraries.  This

accounts for the change made in solib.c.  Note that the new code

attempts to match "/libc." via strstr().  That trailing dot (".")

avoids inadvertently matching libraries such as libcrypt (and

all the other many libraries which begin with "libc").

To avoid attempts to load libthread_db when encountering older

versions of libc, we now attempt to find "pthread_create" (which is a

symbol that we'd expect to be in any pthread library) in the

associated objfile.  This accounts for the changes in

linux-thread-db.c.

I think that other small adjustments will need to be made elsewhere

too.  I've been working through regressions on my glibc-2.33.9000

machine; I've fixed some fairly "obvious" changes in the testsuite

(which are in other commits).  For the rest, it's not yet clear to me

whether the handful of remaining failures represent a problem in glibc

or gdb.  I'm still investigating, however, I'll note that these are

problems that I only see on my glibc-2.33.9000 machine.

gdb/ChangeLog:

	* solib.c (libpthread_name_p): Match "libc" in addition

	to "libpthread".

	* linux-thread-db.c (libpthread_objfile_p): New function.

	(libpthread_name_p): Adjust preexisting callers to use

	libpthread_objfile_p().

diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c

--- a/gdb/linux-thread-db.c

+++ b/gdb/linux-thread-db.c

@@ -800,6 +800,24 @@ check_thread_db (struct thread_db_info *info, bool log_progress)

   return test_passed;

 }

+/* Predicate which tests whether objfile OBJ refers to the library

+   containing pthread related symbols.  Historically, this library has

+   been named in such a way that looking for "libpthread" in the name

+   was sufficient to identify it.  As of glibc-2.34, the C library

+   (libc) contains the thread library symbols.  Therefore we check

+   that the name matches a possible thread library, but we also check

+   that it contains at least one of the symbols (pthread_create) that

+   we'd expect to find in the thread library.  */

+

+static bool

+libpthread_objfile_p (objfile *obj)

+{

+  return (libpthread_name_p (objfile_name (obj))

+          && lookup_minimal_symbol ("pthread_create",

+	                            NULL,

+				    obj).minsym != NULL);

+}

+

 /* Attempt to initialize dlopen()ed libthread_db, described by INFO.

    Return true on success.

    Failure could happen if libthread_db does not have symbols we expect,

@@ -1072,7 +1090,7 @@ try_thread_db_load_from_pdir (const char *subdir)

     return false;

   for (objfile *obj : current_program_space->objfiles ())

-    if (libpthread_name_p (objfile_name (obj)))

+    if (libpthread_objfile_p (obj))

       {

 	if (try_thread_db_load_from_pdir_1 (obj, subdir))

 	  return true;

@@ -1181,7 +1199,7 @@ static bool

 has_libpthread (void)

 {

   for (objfile *obj : current_program_space->objfiles ())

-    if (libpthread_name_p (objfile_name (obj)))

+    if (libpthread_objfile_p (obj))

       return true;

   return false;

@@ -1295,7 +1313,7 @@ thread_db_new_objfile (struct objfile *objfile)

 	 of the list of shared libraries to load, and in an app of several

 	 thousand shared libraries, this can otherwise be painful.  */

       && ((objfile->flags & OBJF_MAINLINE) != 0

-	  || libpthread_name_p (objfile_name (objfile))))

+	  || libpthread_objfile_p (objfile)))

     check_for_thread_db ();

 }

diff --git a/gdb/solib.c b/gdb/solib.c

--- a/gdb/solib.c

+++ b/gdb/solib.c

@@ -906,12 +906,17 @@ Do you need \"set solib-search-path\" or \"set sysroot\"?"),

    Uses a fairly simplistic heuristic approach where we check

    the file name against "/libpthread".  This can lead to false

-   positives, but this should be good enough in practice.  */

+   positives, but this should be good enough in practice.

+

+   As of glibc-2.34, functions formerly residing in libpthread have

+   been moved to libc, so "/libc." needs to be checked too.  (Matching

+   the "." will avoid matching libraries such as libcrypt.) */

 bool

 libpthread_name_p (const char *name)

 {

-  return (strstr (name, "/libpthread") != NULL);

+  return (strstr (name, "/libpthread") != NULL

+          || strstr (name, "/libc.") != NULL );

 }

 /* Return non-zero if SO is the libpthread shared library.  */