[PATCH] nptl: Export libthread_db-used symbols under GLIBC_PRIVATE
Florian Weimer
fweimer@redhat.com
Thu Jun 17 19:23:53 GMT 2021
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;
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