[PATCH v2] nptl_db: disable DT_RELR on libthread_db.so

[Paul E. Murphy]

Continued from

https://sourceware.org/pipermail/libc-alpha/2022-June/139357.html

---8<---

Some nptl tests inadvertently use the host's gdb to verify
libthread_db.so, which is loaded with the host's runtime.  This causes
a couple of test failures when the host glibc does not support DT_RELR.

The not correct, but simple, workaround is to build without DT_RELR
as this library is otherwise likely to load on glibc 2.17 and newer
today.

This allows tst-pthread-gdb-attach{,-static} to continue working
when testing on a gdb loaded with an older glibc.

This avoids a failure in tst-pthread-gdb-attach similar to:

  Trying host libthread_db library: .../build/glibc/nptl_db/libthread_db.so.1.
  dlopen failed: /lib64/libc.so.6: version `GLIBC_ABI_DT_RELR' not found (required by .../build/glibc/nptl_db/libthread_db.so.1).
---
 nptl_db/Makefile | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/nptl_db/Makefile b/nptl_db/Makefile
index ed923a41e5..2360e53c88 100644
--- a/nptl_db/Makefile
+++ b/nptl_db/Makefile
@@ -49,6 +49,12 @@ libthread_db-inhibit-o = $(filter-out .os,$(object-suffixes))
 # The ps_* callback functions are not defined.
 libthread_db.so-no-z-defs = yes
 
+# This is a hack.  This is not the correct solution.  When this glibc
+# is tested, the gdb used could be loaded by the host glibc, which
+# may not support DT_RELR, and report a failure instead of unsupported.
+# For now, build this without DT_RELR support to avoid this situation.
+libthread_db.so-no-dt-relr = yes
+
 tests-special += $(objpfx)db-symbols.out
 
 include ../Rules
-- 
2.36.1