[PATCH] nptl: Export libthread_db-used symbols under GLIBC_PRIVATE

[Florian Weimer <fweimer@redhat.com>]

Kevin, this *almost* gives us the perfect debugging experience with your
patched GDB in Fedora 35, according to my preliminary tests.  A build
with the patch is running here:

  <https://koji.fedoraproject.org/koji/buildinfo?buildID=1773177>

However, it seems that GDB still needs pthread_create in the .symtab to
trigger loading of libpthread_db.  A fully stripped libc.so.6 without
.symtab does not trigger loading in my experiments.  (The other symbols
we preserve for valgrind's sake and are immaterial to GDB.)  In other
words,

  cp /lib64/libc.so.6 . ; strip libc.so.6 ; LD_LIBRARY_PATH=. gdb …

does not result in working thread debugging.

If the pthread_create .symtab requirement is too difficult to work
around, we might as well put the _thread_db_* symbols into .symtab and
tell distributions to use:

  strip -w -K pthread_create -K _thread_db_\* libc.so.6

But then we'd need two categories of symbols in the internal consistency
check for nptl_db (the db-symbol.awk file), so maybe that's overdoing
things for a slightly smaller .dynsym size.

Thanks,
Florian

8<------------------------------------------------------------------8<
This allows distributions to strip debugging information from
libc.so.6 without impacting the debugging experience.

nptl_version had to be renamed to __nptl_version to avoid
namespace issues.
---
 nptl/Versions          | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++
 nptl/pthread_create.c  | 13 +++++++-----
 nptl_db/Makefile       |  2 +-
 nptl_db/db-symbols.awk |  4 +++-
 nptl_db/structs.def    |  2 +-
 nptl_db/td_ta_new.c    |  2 +-
 6 files changed, 70 insertions(+), 9 deletions(-)

diff --git a/nptl/Versions b/nptl/Versions
index 62bb939d54..c03ed92848 100644
--- a/nptl/Versions
+++ b/nptl/Versions
@@ -403,10 +403,14 @@ libc {
     __nptl_deallocate_tsd;
     __nptl_death_event;
     __nptl_free_tcb;
+    __nptl_last_event;
     __nptl_nthreads;
+    __nptl_rtld_global;
     __nptl_setxid_sighandler;
     __nptl_stack_list_add;
     __nptl_stack_list_del;
+    __nptl_threads_events;
+    __nptl_version;
     __pthread_attr_copy;
     __pthread_attr_destroy;
     __pthread_attr_init;
@@ -430,6 +434,58 @@ libc {
     __pthread_unwind;
     __sched_fifo_max_prio;
     __sched_fifo_min_prio;
+    _thread_db___nptl_last_event;
+    _thread_db___nptl_rtld_global;
+    _thread_db_const_thread_area;
+    _thread_db_dtv_dtv;
+    _thread_db_dtv_slotinfo_gen;
+    _thread_db_dtv_slotinfo_list_len;
+    _thread_db_dtv_slotinfo_list_next;
+    _thread_db_dtv_slotinfo_list_slotinfo;
+    _thread_db_dtv_slotinfo_map;
+    _thread_db_dtv_t_counter;
+    _thread_db_dtv_t_pointer_val;
+    _thread_db_link_map_l_tls_modid;
+    _thread_db_link_map_l_tls_offset;
+    _thread_db_list_t_next;
+    _thread_db_list_t_prev;
+    _thread_db_pthread_cancelhandling;
+    _thread_db_pthread_dtvp;
+    _thread_db_pthread_eventbuf;
+    _thread_db_pthread_eventbuf_eventmask;
+    _thread_db_pthread_eventbuf_eventmask_event_bits;
+    _thread_db_pthread_key_data_data;
+    _thread_db_pthread_key_data_level2_data;
+    _thread_db_pthread_key_data_seq;
+    _thread_db_pthread_key_struct_destr;
+    _thread_db_pthread_key_struct_seq;
+    _thread_db_pthread_list;
+    _thread_db_pthread_nextevent;
+    _thread_db_pthread_report_events;
+    _thread_db_pthread_schedparam_sched_priority;
+    _thread_db_pthread_schedpolicy;
+    _thread_db_pthread_specific;
+    _thread_db_pthread_start_routine;
+    _thread_db_pthread_tid;
+    _thread_db_register32;
+    _thread_db_register32_thread_area;
+    _thread_db_register64;
+    _thread_db_register64_thread_area;
+    _thread_db_rtld_global__dl_stack_used;
+    _thread_db_rtld_global__dl_stack_user;
+    _thread_db_rtld_global__dl_tls_dtv_slotinfo_list;
+    _thread_db_sizeof_dtv_slotinfo;
+    _thread_db_sizeof_dtv_slotinfo_list;
+    _thread_db_sizeof_list_t;
+    _thread_db_sizeof_pthread;
+    _thread_db_sizeof_pthread_key_data;
+    _thread_db_sizeof_pthread_key_data_level2;
+    _thread_db_sizeof_pthread_key_struct;
+    _thread_db_sizeof_td_eventbuf_t;
+    _thread_db_sizeof_td_thr_events_t;
+    _thread_db_td_eventbuf_t_eventdata;
+    _thread_db_td_eventbuf_t_eventnum;
+    _thread_db_td_thr_events_t_event_bits;
   }
 }
 
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index 3f017f1e26..d1b6817a81 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -43,21 +43,24 @@
 
 
 /* Globally enabled events.  */
-static td_thr_events_t __nptl_threads_events __attribute_used__;
+td_thr_events_t __nptl_threads_events __attribute__ ((nocommon));
+libc_hidden_proto (__nptl_threads_events)
+libc_hidden_data_def (__nptl_threads_events)
 
 /* Pointer to descriptor with the last event.  */
-static struct pthread *__nptl_last_event __attribute_used__;
+struct pthread *__nptl_last_event __attribute__ ((nocommon));
+libc_hidden_proto (__nptl_last_event)
+libc_hidden_data_def (__nptl_last_event)
 
 #ifdef SHARED
 /* This variable is used to access _rtld_global from libthread_db.  If
    GDB loads libpthread before ld.so, it is not possible to resolve
    _rtld_global directly during libpthread initialization.  */
-static struct rtld_global *__nptl_rtld_global __attribute_used__
-  = &_rtld_global;
+struct rtld_global *__nptl_rtld_global = &_rtld_global;
 #endif
 
 /* Version of the library, used in libthread_db to detect mismatches.  */
-static const char nptl_version[] __attribute_used__ = VERSION;
+const char __nptl_version[] = VERSION;
 
 /* This performs the initialization necessary when going from
    single-threaded to multi-threaded mode for the first time.  */
diff --git a/nptl_db/Makefile b/nptl_db/Makefile
index ea721c1dcf..4cc51c0e7b 100644
--- a/nptl_db/Makefile
+++ b/nptl_db/Makefile
@@ -57,7 +57,7 @@ include ../Rules
 
 $(objpfx)db-symbols.out: $(objpfx)db-symbols.v.i \
 			 $(common-objpfx)libc.so
-	LC_ALL=C $(READELF) -W -s $(filter %.so,$^) | $(AWK) -f $< > $@; \
+	LC_ALL=C $(READELF) -W -D -s $(filter %.so,$^) | $(AWK) -f $< > $@; \
 	$(evaluate-test)
 
 $(objpfx)db-symbols.v.i: db-symbols.awk
diff --git a/nptl_db/db-symbols.awk b/nptl_db/db-symbols.awk
index 6f326cf379..2033f95e38 100644
--- a/nptl_db/db-symbols.awk
+++ b/nptl_db/db-symbols.awk
@@ -13,7 +13,7 @@ BEGIN {
    in_symtab = 0;
 }
 
-/Symbol table '.symtab'/ { in_symtab=1; next }
+/Symbol table for image/ { in_symtab=1; next }
 NF == 0 { in_symtab=0; next }
 
 !in_symtab { next }
@@ -24,6 +24,7 @@ END {
   status = 0;
 
   for (s in required) {
+    s = s "@@GLIBC_PRIVATE"
     if (s in seen) print s, "ok";
     else {
       status = 1;
@@ -33,6 +34,7 @@ END {
 
   any = "";
   for (s in th_unique) {
+    s = s "@@GLIBC_PRIVATE"
     if (s in seen) {
       any = s;
       break;
diff --git a/nptl_db/structs.def b/nptl_db/structs.def
index 6a726f207e..e2e51acc39 100644
--- a/nptl_db/structs.def
+++ b/nptl_db/structs.def
@@ -77,7 +77,7 @@ DB_STRUCT (td_eventbuf_t)
 DB_STRUCT_FIELD (td_eventbuf_t, eventnum)
 DB_STRUCT_FIELD (td_eventbuf_t, eventdata)
 
-DB_SYMBOL (nptl_version)
+DB_SYMBOL (__nptl_version)
 DB_MAIN_SYMBOL (__nptl_create_event)
 DB_MAIN_SYMBOL (__nptl_death_event)
 DB_SYMBOL (__nptl_threads_events)
diff --git a/nptl_db/td_ta_new.c b/nptl_db/td_ta_new.c
index 501d922ea2..eeca29d5a0 100644
--- a/nptl_db/td_ta_new.c
+++ b/nptl_db/td_ta_new.c
@@ -39,7 +39,7 @@ td_ta_new (struct ps_prochandle *ps, td_thragent_t **ta)
   LOG ("td_ta_new");
 
   /* Check whether the versions match.  */
-  if (td_lookup (ps, SYM_nptl_version, &versaddr) != PS_OK)
+  if (td_lookup (ps, SYM___nptl_version, &versaddr) != PS_OK)
     return TD_NOLIBTHREAD;
   if (ps_pdread (ps, versaddr, versbuf, sizeof (versbuf)) != PS_OK)
     return TD_ERR;