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Message-Id: <20210830173844.458727-3-hjl.tools@gmail.com>
Date: Mon, 30 Aug 2021 10:38:44 -0700
From: "H.J. Lu" <hjl.tools@...il.com>
To: libc-alpha@...rceware.org
Cc: gdb@...rceware.org,
libc-coord@...ts.openwall.com,
Florian Weimer <fweimer@...hat.com>,
Daniel Walker <danielwa@...co.com>
Subject: [PATCH v6 2/2] Extend struct r_debug to support multiple namespaces
Glibc does not provide an interface for debugger to access libraries
loaded in multiple namespaces via dlmopen.
The current rtld-debugger interface is described in the file:
elf/rtld-debugger-interface.txt
under the "Standard debugger interface" heading. This interface only
provides access to the first link-map (LM_ID_BASE).
1. Bump r_version to 2. This triggers the GDB bug:
https://sourceware.org/bugzilla/show_bug.cgi?id=28236
2. Add struct r_debug_extended to extend struct r_debug into a linked-list,
where each element correlates to an unique namespace.
3. Remove the empty namespace from the namespace linked list and clear
its r_version field.
4. Add the new namespace, whose r_version field is 0, to the namespace
linked list.
5. Initialize the r_debug_extended structure only if its r_version field
is 0 and update its r_map field if it is NULL.
6. Add a hidden symbol, _r_debug_extended, for struct r_debug_extended.
7. Provide the compatibility symbol, _r_debug, with size of struct r_debug,
as an alise of _r_debug_extended, for programs which reference _r_debug.
---
NEWS | 9 ++++-
csu/Makefile | 3 ++
csu/rtld-sizes.sym | 4 ++
elf/Makefile | 24 +++++++++++-
elf/dl-close.c | 21 ++++++++++
elf/dl-debug-symbols-gen.c | 24 ++++++++++++
elf/dl-debug-symbols.S | 37 ++++++++++++++++++
elf/dl-debug.c | 46 ++++++++++++----------
elf/dl-reloc-static-pie.c | 2 +-
elf/link.h | 36 ++++++++++++-----
elf/rtld-debugger-interface.txt | 14 +++++++
elf/rtld.c | 2 +-
elf/tst-dlmopen4.c | 68 +++++++++++++++++++++++++++++++++
include/link.h | 4 ++
sysdeps/generic/ldsodefs.h | 8 ++--
15 files changed, 263 insertions(+), 39 deletions(-)
create mode 100644 csu/rtld-sizes.sym
create mode 100644 elf/dl-debug-symbols-gen.c
create mode 100644 elf/dl-debug-symbols.S
create mode 100644 elf/tst-dlmopen4.c
diff --git a/NEWS b/NEWS
index 79c895e382..9e59cde737 100644
--- a/NEWS
+++ b/NEWS
@@ -9,11 +9,16 @@ Version 2.35
Major new features:
- [Add new features here]
+* Bump r_version in the debugger interface to 2 and add a new field,
+ r_next, support multiple namespaces.
Deprecated and removed features, and other changes affecting compatibility:
- [Add deprecations, removals and changes affecting compatibility here]
+* The r_version update in the debugger interface makes the glibc binary
+ incompatible with GDB binaries built without the following commits:
+
+ c0154a4a21a gdb: Don't assume r_ldsomap when r_version > 1 on Linux
+ 4eb629d50d4 gdbserver: Check r_version < 1 for Linux debugger interface
Changes to build and runtime requirements:
diff --git a/csu/Makefile b/csu/Makefile
index 3054329cea..e2390e4a7d 100644
--- a/csu/Makefile
+++ b/csu/Makefile
@@ -88,6 +88,9 @@ endif
before-compile += $(objpfx)abi-tag.h
generated += abi-tag.h
+# Put it here to generate it earlier.
+gen-as-const-headers += rtld-sizes.sym
+
# These are the special initializer/finalizer files. They are always the
# first and last file in the link. crti.o ... crtn.o define the global
# "functions" _init and _fini to run the .init and .fini sections.
diff --git a/csu/rtld-sizes.sym b/csu/rtld-sizes.sym
new file mode 100644
index 0000000000..40dd8edaec
--- /dev/null
+++ b/csu/rtld-sizes.sym
@@ -0,0 +1,4 @@
+#include <link.h>
+
+--
+COMPAT_R_DEBUG_SIZE sizeof (struct r_debug)
diff --git a/elf/Makefile b/elf/Makefile
index 9f3fadc37e..d0d226fe9a 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -35,7 +35,8 @@ dl-routines = $(addprefix dl-,load lookup object reloc deps \
execstack open close trampoline \
exception sort-maps lookup-direct \
call-libc-early-init write \
- thread_gscope_wait tls_init_tp)
+ thread_gscope_wait tls_init_tp \
+ debug-symbols)
ifeq (yes,$(use-ldconfig))
dl-routines += dl-cache
endif
@@ -203,7 +204,7 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
tst-tls16 tst-tls17 tst-tls18 tst-tls19 tst-tls-dlinfo \
tst-align tst-align2 \
tst-dlmodcount tst-dlopenrpath tst-deep1 \
- tst-dlmopen1 tst-dlmopen3 \
+ tst-dlmopen1 tst-dlmopen3 tst-dlmopen4 \
unload3 unload4 unload5 unload6 unload7 unload8 tst-global1 order2 \
tst-audit1 tst-audit2 tst-audit8 tst-audit9 \
tst-addr1 tst-thrlock \
@@ -674,6 +675,23 @@ LC_ALL=C sed $(ldd-rewrite) < $< \
endef
endif
+ifeq ($(build-shared),yes)
+# dl-debug-compat-symbols.os and dl-debug-compat-symbols.o are assembly
+# codes included in dl-debug-symbols.S.
+generated += dl-debug-compat-symbols.os dl-debug-compat-symbols.o
+
+libof-dl-debug-compat-symbols = rtld
+
+$(objpfx)dl-debug-compat-symbols.os: dl-debug-symbols-gen.c
+ $(compile-command.c) -S
+
+$(objpfx)dl-debug-compat-symbols.o: dl-debug-symbols-gen.c
+ $(compile-command.c) -S
+
+$(objpfx)dl-debug-symbols.os: $(objpfx)dl-debug-compat-symbols.os
+$(objpfx)dl-debug-symbols.o: $(objpfx)dl-debug-compat-symbols.o
+endif
+
$(objpfx)ldd: ldd.bash.in $(common-objpfx)soversions.mk \
$(common-objpfx)config.make
$(gen-ldd)
@@ -1244,6 +1262,8 @@ $(objpfx)tst-dlmopen2.out: $(objpfx)tst-dlmopen1mod.so
$(objpfx)tst-dlmopen3.out: $(objpfx)tst-dlmopen1mod.so
+$(objpfx)tst-dlmopen4.out: $(objpfx)tst-dlmopen1mod.so
+
$(objpfx)tst-audit1.out: $(objpfx)tst-auditmod1.so
tst-audit1-ENV = LD_AUDIT=$(objpfx)tst-auditmod1.so
diff --git a/elf/dl-close.c b/elf/dl-close.c
index f39001cab9..43873d2543 100644
--- a/elf/dl-close.c
+++ b/elf/dl-close.c
@@ -709,6 +709,27 @@ _dl_close_worker (struct link_map *map, bool force)
assert (nsid != LM_ID_BASE);
ns->_ns_loaded = imap->l_next;
+ if (ns->_ns_loaded == NULL)
+ {
+ /* Remove the empty namespace from the namespace linked
+ list. */
+ struct r_debug_extended **pp, *p;
+
+ for (pp = &_r_debug_extended.r_next;
+ (p = *pp) != NULL;
+ pp = &p->r_next)
+ if (p == &ns->_ns_debug)
+ {
+ /* Remove the empty namespace. */
+ *pp = p->r_next;
+
+ /* Clear r_version to indicate that it is
+ unused. */
+ p->base.r_version = 0;
+ break;
+ }
+ }
+
/* Update the pointer to the head of the list
we leave for debuggers to examine. */
r->r_map = (void *) ns->_ns_loaded;
diff --git a/elf/dl-debug-symbols-gen.c b/elf/dl-debug-symbols-gen.c
new file mode 100644
index 0000000000..2406260bcb
--- /dev/null
+++ b/elf/dl-debug-symbols-gen.c
@@ -0,0 +1,24 @@
+/* Generate the _r_debug_extended symbol used to communicate dynamic
+ linker state to the debugger at runtime.
+ Copyright (C) 2021 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <link.h>
+
+/* This structure communicates dl state to the debugger. The debugger
+ finds it via the DT_DEBUG entry in the dynamic section. */
+struct r_debug_extended _r_debug_extended;
diff --git a/elf/dl-debug-symbols.S b/elf/dl-debug-symbols.S
new file mode 100644
index 0000000000..902b9d4a3c
--- /dev/null
+++ b/elf/dl-debug-symbols.S
@@ -0,0 +1,37 @@
+/* Define symbols used to communicate dynamic linker state to the
+ debugger at runtime.
+ Copyright (C) 2021 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <rtld-sizes.h>
+
+/* Define 2 symbols, _r_debug_extended and _r_debug, which is an alias
+ of _r_debug_extended, but with the size of struct r_debug and is
+ provided as a compatibility symbol. Since in assembly codes, the
+ symbol alias with a different size must be placed after the original
+ symbol and we can't control their orders generated by compiler, we
+ place them directly in assembly codes. dl-debug-compat-symbols.[o|os]
+ generated from dl-debug-symbols-gen.c defines _r_debug_extended. */
+
+#ifdef SHARED
+# include "dl-debug-compat-symbols.os"
+#else
+# include "dl-debug-compat-symbols.o"
+#endif
+
+declare_object_symbol_alias (_r_debug, _r_debug_extended,
+ COMPAT_R_DEBUG_SIZE);
diff --git a/elf/dl-debug.c b/elf/dl-debug.c
index 2cd5f09753..81dd40960a 100644
--- a/elf/dl-debug.c
+++ b/elf/dl-debug.c
@@ -30,37 +30,43 @@ extern const int verify_link_map_members[(VERIFY_MEMBER (l_addr)
&& VERIFY_MEMBER (l_prev))
? 1 : -1];
-/* This structure communicates dl state to the debugger. The debugger
- normally finds it via the DT_DEBUG entry in the dynamic section, but in
- a statically-linked program there is no dynamic section for the debugger
- to examine and it looks for this particular symbol name. */
-struct r_debug _r_debug;
-
-
-/* Initialize _r_debug if it has not already been done. The argument is
- the run-time load address of the dynamic linker, to be put in
- _r_debug.r_ldbase. Returns the address of _r_debug. */
+/* Initialize _r_debug_extended if it has not already been done. The
+ argument is the run-time load address of the dynamic linker, to be
+ put in _r_debug_extended.r_ldbase. Returns the address of
+ _r_debug_extended. */
struct r_debug *
_dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
{
- struct r_debug *r;
+ struct r_debug_extended *r;
if (ns == LM_ID_BASE)
- r = &_r_debug;
+ r = &_r_debug_extended;
else
- r = &GL(dl_ns)[ns]._ns_debug;
+ {
+ r = &GL(dl_ns)[ns]._ns_debug;
+ if (DL_NNS > 1 && r->base.r_version == 0)
+ {
+ /* Add the new namespace to the linked list. */
+ r->r_next = _r_debug_extended.r_next;
+ _r_debug_extended.r_next = r;
+ }
+ }
- if (r->r_map == NULL || ldbase != 0)
+ if (r->base.r_version == 0)
{
- /* Tell the debugger where to find the map of loaded objects. */
- r->r_version = 1 /* R_DEBUG_VERSION XXX */;
- r->r_ldbase = ldbase ?: _r_debug.r_ldbase;
- r->r_map = (void *) GL(dl_ns)[ns]._ns_loaded;
- r->r_brk = (ElfW(Addr)) &_dl_debug_state;
+ /* Tell the debugger where to find the map of loaded objects.
+ Bump r_version to 2 for the r_next field. */
+ r->base.r_version = 2;
+ r->base.r_ldbase = ldbase ?: _r_debug_extended.base.r_ldbase;
+ r->base.r_brk = (ElfW(Addr)) &_dl_debug_state;
+ r->r_next = NULL;
}
- return r;
+ if (r->base.r_map == NULL)
+ r->base.r_map = (void *) GL(dl_ns)[ns]._ns_loaded;
+
+ return &r->base;
}
diff --git a/elf/dl-reloc-static-pie.c b/elf/dl-reloc-static-pie.c
index d5bd2f31e9..289651b341 100644
--- a/elf/dl-reloc-static-pie.c
+++ b/elf/dl-reloc-static-pie.c
@@ -51,7 +51,7 @@ _dl_relocate_static_pie (void)
ELF_DYNAMIC_RELOCATE (main_map, 0, 0, 0);
main_map->l_relocated = 1;
- /* Initialize _r_debug. */
+ /* Initialize _r_debug_extended. */
struct r_debug *r = _dl_debug_initialize (0, LM_ID_BASE);
r->r_state = RT_CONSISTENT;
diff --git a/elf/link.h b/elf/link.h
index ff3a85c847..a297318236 100644
--- a/elf/link.h
+++ b/elf/link.h
@@ -34,14 +34,13 @@
#include <bits/elfclass.h> /* Defines __ELF_NATIVE_CLASS. */
#include <bits/link.h>
-/* Rendezvous structure used by the run-time dynamic linker to communicate
- details of shared object loading to the debugger. If the executable's
- dynamic section has a DT_DEBUG element, the run-time linker sets that
- element's value to the address where this structure can be found. */
+/* The legacy rendezvous structure used by the run-time dynamic linker to
+ communicate details of shared object loading to the debugger. */
struct r_debug
{
- int r_version; /* Version number for this protocol. */
+ /* Version number for this protocol. It should be greater than 0. */
+ int r_version;
struct link_map *r_map; /* Head of the chain of loaded objects. */
@@ -63,16 +62,35 @@ struct r_debug
ElfW(Addr) r_ldbase; /* Base address the linker is loaded at. */
};
-/* This is the instance of that structure used by the dynamic linker. */
+/* This is the compatibility symbol of that structure provided by the
+ dynamic linker. */
extern struct r_debug _r_debug;
+/* The extended rendezvous structure used by the run-time dynamic linker
+ to communicate details of shared object loading to the debugger. If
+ the executable's dynamic section has a DT_DEBUG element, the run-time
+ linker sets that element's value to the address where this structure
+ can be found. */
+
+struct r_debug_extended
+ {
+ struct r_debug base;
+
+ /* The following field is added by r_version == 2. */
+
+ /* Link to the next r_debug_extended structure. Each r_debug_extended
+ structure represents a different namespace. The first
+ r_debug_extended structure is for the default namespace. */
+ struct r_debug_extended *r_next;
+ };
+
/* This symbol refers to the "dynamic structure" in the `.dynamic' section
of whatever module refers to `_DYNAMIC'. So, to find its own
- `struct r_debug', a program could do:
+ `struct r_debug_extended', a program could do:
for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn)
if (dyn->d_tag == DT_DEBUG)
- r_debug = (struct r_debug *) dyn->d_un.d_ptr;
- */
+ r_debug_extended = (struct r_debug_extended *) dyn->d_un.d_ptr;
+ */
extern ElfW(Dyn) _DYNAMIC[];
/* Structure describing a loaded shared object. The `l_next' and `l_prev'
diff --git a/elf/rtld-debugger-interface.txt b/elf/rtld-debugger-interface.txt
index 61bc99e4b0..f6aaa28706 100644
--- a/elf/rtld-debugger-interface.txt
+++ b/elf/rtld-debugger-interface.txt
@@ -9,6 +9,9 @@ structure can be found.
The r_debug structure contains (amongst others) the following fields:
+ int r_version:
+ Version number for this protocol. It should be greater than 0.
+
struct link_map *r_map:
A linked list of loaded objects.
@@ -32,6 +35,17 @@ but there is no way for the debugger to discover whether any of the
objects in the link-map have been relocated or not.
+Extension to the r_debug structure
+==================================
+
+The r_debug_extended structure is an extension of the r_debug interface.
+If r_version is 2, one additional field is available:
+
+ struct r_debug_extended *r_next;
+ Link to the next r_debug_extended structure. Each r_debug_extended
+ structure represents a different namespace. The first r_debug_extended
+ structure is for the default namespace.
+
Probe-based debugger interface
==============================
diff --git a/elf/rtld.c b/elf/rtld.c
index 878e6480f4..7f80378fb4 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -1660,7 +1660,7 @@ dl_main (const ElfW(Phdr) *phdr,
objects. */
call_init_paths (&state);
- /* Initialize _r_debug. */
+ /* Initialize _r_debug_extended. */
struct r_debug *r = _dl_debug_initialize (GL(dl_rtld_map).l_addr,
LM_ID_BASE);
r->r_state = RT_CONSISTENT;
diff --git a/elf/tst-dlmopen4.c b/elf/tst-dlmopen4.c
new file mode 100644
index 0000000000..7a6c502e8c
--- /dev/null
+++ b/elf/tst-dlmopen4.c
@@ -0,0 +1,68 @@
+/* Test struct r_debug_extended via DT_DEBUG.
+ Copyright (C) 2021 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <stdio.h>
+#include <link.h>
+#include <stdlib.h>
+#include <string.h>
+#include <gnu/lib-names.h>
+#include <support/xdlfcn.h>
+#include <support/check.h>
+#include <support/test-driver.h>
+
+#ifndef ELF_MACHINE_GET_R_DEBUG
+# define ELF_MACHINE_GET_R_DEBUG(d) \
+ (__extension__ ({ \
+ struct r_debug_extended *debug; \
+ if ((d)->d_tag == DT_DEBUG) \
+ debug = (struct r_debug_extended *) (d)->d_un.d_ptr; \
+ else \
+ debug = NULL; \
+ debug; }))
+#endif
+
+static int
+do_test (void)
+{
+ void *h = xdlmopen (LM_ID_NEWLM, "$ORIGIN/tst-dlmopen1mod.so",
+ RTLD_LAZY);
+
+ int status = EXIT_FAILURE;
+ ElfW(Dyn) *d;
+ for (d = _DYNAMIC; d->d_tag != DT_NULL; ++d)
+ {
+ struct r_debug_extended *debug = ELF_MACHINE_GET_R_DEBUG (d);
+ if (debug != NULL)
+ {
+ TEST_VERIFY_EXIT (debug->base.r_version == 2);
+ TEST_VERIFY_EXIT (debug->r_next != NULL);
+ TEST_VERIFY_EXIT (debug->r_next->r_next == NULL);
+ TEST_VERIFY_EXIT (debug->r_next->base.r_map != NULL);
+ TEST_VERIFY_EXIT (debug->r_next->base.r_map->l_name != NULL);
+ const char *name = basename (debug->r_next->base.r_map->l_name);
+ TEST_VERIFY_EXIT (strcmp (name, "tst-dlmopen1mod.so") == 0);
+ status = EXIT_SUCCESS;
+ }
+ }
+
+ xdlclose (h);
+
+ return status;
+}
+
+#include <support/test-driver.c>
diff --git a/include/link.h b/include/link.h
index 4af16cb596..7b8250db36 100644
--- a/include/link.h
+++ b/include/link.h
@@ -353,6 +353,10 @@ struct auditstate
};
+/* This is the hidden instance of struct r_debug_extended used by the
+ dynamic linker. */
+extern struct r_debug_extended _r_debug_extended attribute_hidden;
+
#if __ELF_NATIVE_CLASS == 32
# define symbind symbind32
#elif __ELF_NATIVE_CLASS == 64
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 9c15259236..813f8659a1 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -355,7 +355,7 @@ struct rtld_global
void (*free) (void *);
} _ns_unique_sym_table;
/* Keep track of changes to each namespace' list. */
- struct r_debug _ns_debug;
+ struct r_debug_extended _ns_debug;
} _dl_ns[DL_NNS];
/* One higher than index of last used namespace. */
EXTERN size_t _dl_nns;
@@ -1093,9 +1093,9 @@ extern void _dl_sort_maps (struct link_map **maps, unsigned int nmaps,
extern void _dl_debug_state (void);
rtld_hidden_proto (_dl_debug_state)
-/* Initialize `struct r_debug' if it has not already been done. The
- argument is the run-time load address of the dynamic linker, to be put
- in the `r_ldbase' member. Returns the address of the structure. */
+/* Initialize `struct r_debug_extended' if it has not already been done.
+ The argument is the run-time load address of the dynamic linker, to
+ be put in the `r_ldbase' member. Returns the address of the structure. */
extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
attribute_hidden;
--
2.31.1
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