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Extend struct r_debug to support multiple namespaces [BZ #15971] 

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 when multiple namespaces are used.  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. Initialize the r_debug_extended structure.  Bump r_version to 2 for
the new namespace and add the new namespace to the namespace linked list.
4. Add _dl_debug_update to return the address of struct r_debug' of a
namespace.
5. Add a hidden symbol, _r_debug_extended, for struct r_debug_extended.
6. Provide the symbol, _r_debug, with size of struct r_debug, as an alias
of _r_debug_extended, for programs which reference _r_debug.

This fixes BZ #15971.

Reviewed-by: Florian Weimer <fweimer@redhat.com>
This commit is contained in:
H.J. Lu 2021-08-17 19:35:48 -07:00
parent 885762aa31
commit a93d9e03a3
16 changed files with 258 additions and 46 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
NEWS
View File

@ -9,6 +9,9 @@ Version 2.35
Major new features:
* Bump r_version in the debugger interface to 2 and add a new field,
r_next, support multiple namespaces.
* Support for the C.UTF-8 locale has been added to glibc. The locale
supports full code-point sorting for all valid Unicode code points. A
limitation in the framework for fnmatch, regexec, and regcomp requires
@ -28,7 +31,13 @@ Major new features:
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
when audit modules or dlmopen are used.
Changes to build and runtime requirements:

3
csu/Makefile
View File

@ -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.

6
csu/rtld-sizes.sym Normal file
View File

@ -0,0 +1,6 @@
#include <link.h>
--
R_DEBUG_SIZE sizeof (struct r_debug)
R_DEBUG_EXTENDED_SIZE sizeof (struct r_debug_extended)
R_DEBUG_EXTENDED_ALIGN __alignof (struct r_debug_extended)

7
elf/Makefile
View File

@ -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 \
@ -1244,6 +1245,8 @@ $(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

2
elf/dl-close.c
View File

@ -500,7 +500,7 @@ _dl_close_worker (struct link_map *map, bool force)
#endif
/* Notify the debugger we are about to remove some loaded objects. */
struct r_debug *r = _dl_debug_initialize (0, nsid);
struct r_debug *r = _dl_debug_update (nsid);
r->r_state = RT_DELETE;
_dl_debug_state ();
LIBC_PROBE (unmap_start, 2, nsid, r);

36
elf/dl-debug-symbols.S Normal file
View File

@ -0,0 +1,36 @@
/* 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. */
.globl _r_debug
.type _r_debug, %object
.size _r_debug, R_DEBUG_SIZE
.hidden _r_debug_extended
.globl _r_debug_extended
.type _r_debug_extended, %object
.size _r_debug_extended, R_DEBUG_EXTENDED_SIZE
.section .bss
.balign R_DEBUG_EXTENDED_ALIGN
_r_debug:
_r_debug_extended:
.zero R_DEBUG_EXTENDED_SIZE

83
elf/dl-debug.c
View File

@ -30,37 +30,80 @@ 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;
/* Update the `r_map' member and return the address of `struct r_debug'
of the namespace NS. */
struct r_debug *
_dl_debug_update (Lmid_t ns)
{
struct r_debug_extended *r;
if (ns == LM_ID_BASE)
r = &_r_debug_extended;
else
r = &GL(dl_ns)[ns]._ns_debug;
if (r->base.r_map == NULL)
atomic_store_release (&r->base.r_map,
(void *) GL(dl_ns)[ns]._ns_loaded);
return &r->base;
}
/* 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 for the namespace NS. LDBASE is the
run-time load address of the dynamic linker, to be put in
_r_debug_extended.r_ldbase. Return the address of _r_debug. */
struct r_debug *
_dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
{
struct r_debug *r;
struct r_debug_extended *r, **pp = NULL;
if (ns == LM_ID_BASE)
r = &_r_debug;
else
r = &GL(dl_ns)[ns]._ns_debug;
if (r->r_map == NULL || ldbase != 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;
r = &_r_debug_extended;
/* Initialize r_version to 1. */
if (_r_debug_extended.base.r_version == 0)
_r_debug_extended.base.r_version = 1;
}
else if (DL_NNS > 1)
{
r = &GL(dl_ns)[ns]._ns_debug;
if (r->base.r_brk == 0)
{
/* Add the new namespace to the linked list. After a namespace
is initialized, r_brk becomes non-zero. A namespace becomes
empty (r_map == NULL) when it is unused. But it is never
removed from the linked list. */
struct r_debug_extended *p;
for (pp = &_r_debug_extended.r_next;
(p = *pp) != NULL;
pp = &p->r_next)
;
r->base.r_version = 2;
}
}
return r;
if (r->base.r_brk == 0)
{
/* Tell the debugger where to find the map of loaded objects.
This function is called from dlopen. Initialize the namespace
only once. */
r->base.r_ldbase = ldbase ?: _r_debug_extended.base.r_ldbase;
r->base.r_brk = (ElfW(Addr)) &_dl_debug_state;
r->r_next = NULL;
}
if (r->base.r_map == NULL)
atomic_store_release (&r->base.r_map,
(void *) GL(dl_ns)[ns]._ns_loaded);
if (pp != NULL)
{
atomic_store_release (pp, r);
/* Bump r_version to 2 for the new namespace. */
atomic_store_release (&_r_debug_extended.base.r_version, 2);
}
return &r->base;
}

2
elf/dl-load.c
View File

@ -949,7 +949,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
/* Initialize to keep the compiler happy. */
const char *errstring = NULL;
int errval = 0;
struct r_debug *r = _dl_debug_initialize (0, nsid);
struct r_debug *r = _dl_debug_update (nsid);
bool make_consistent = false;
/* Get file information. To match the kernel behavior, do not fill

10
elf/dl-open.c
View File

@ -574,7 +574,7 @@ dl_open_worker (void *a)
if ((mode & RTLD_GLOBAL) && new->l_global == 0)
add_to_global_update (new);
assert (_dl_debug_initialize (0, args->nsid)->r_state == RT_CONSISTENT);
assert (_dl_debug_update (args->nsid)->r_state == RT_CONSISTENT);
return;
}
@ -630,7 +630,7 @@ dl_open_worker (void *a)
#endif
/* Notify the debugger all new objects are now ready to go. */
struct r_debug *r = _dl_debug_initialize (0, args->nsid);
struct r_debug *r = _dl_debug_update (args->nsid);
r->r_state = RT_CONSISTENT;
_dl_debug_state ();
LIBC_PROBE (map_complete, 3, args->nsid, r, new);
@ -830,7 +830,7 @@ no more namespaces available for dlmopen()"));
++GL(dl_nns);
}
_dl_debug_initialize (0, nsid)->r_state = RT_CONSISTENT;
_dl_debug_update (nsid)->r_state = RT_CONSISTENT;
}
/* Never allow loading a DSO in a namespace which is empty. Such
direct placements is only causing problems. Also don't allow
@ -899,7 +899,7 @@ no more namespaces available for dlmopen()"));
the flag here. */
}
assert (_dl_debug_initialize (0, args.nsid)->r_state == RT_CONSISTENT);
assert (_dl_debug_update (args.nsid)->r_state == RT_CONSISTENT);
/* Release the lock. */
__rtld_lock_unlock_recursive (GL(dl_load_lock));
@ -908,7 +908,7 @@ no more namespaces available for dlmopen()"));
_dl_signal_exception (errcode, &exception, NULL);
}
assert (_dl_debug_initialize (0, args.nsid)->r_state == RT_CONSISTENT);
assert (_dl_debug_update (args.nsid)->r_state == RT_CONSISTENT);
/* Release the lock. */
__rtld_lock_unlock_recursive (GL(dl_load_lock));

2
elf/dl-reloc-static-pie.c
View File

@ -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;

35
elf/link.h
View File

@ -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 +62,34 @@ 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 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'

15
elf/rtld-debugger-interface.txt
View File

@ -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 +35,18 @@ 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. A namespace is active
if its r_map field isn't NULL. The first r_debug_extended structure
is for the default namespace.
Probe-based debugger interface
==============================

4
elf/rtld.c
View File

@ -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;
@ -2491,7 +2491,7 @@ dl_main (const ElfW(Phdr) *phdr,
/* Notify the debugger all new objects are now ready to go. We must re-get
the address since by now the variable might be in another object. */
r = _dl_debug_initialize (0, LM_ID_BASE);
r = _dl_debug_update (LM_ID_BASE);
r->r_state = RT_CONSISTENT;
_dl_debug_state ();
LIBC_PROBE (init_complete, 2, LM_ID_BASE, r);

72
elf/tst-dlmopen4.c Normal file
View File

@ -0,0 +1,72 @@
/* 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)
{
ElfW(Dyn) *d;
struct r_debug_extended *debug = NULL;
for (d = _DYNAMIC; d->d_tag != DT_NULL; ++d)
{
debug = ELF_MACHINE_GET_R_DEBUG (d);
if (debug != NULL)
break;
}
TEST_VERIFY_EXIT (debug != NULL);
TEST_COMPARE (debug->base.r_version, 1);
TEST_VERIFY_EXIT (debug->r_next == NULL);
void *h = xdlmopen (LM_ID_NEWLM, "$ORIGIN/tst-dlmopen1mod.so",
RTLD_LAZY);
TEST_COMPARE (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_COMPARE_STRING (name, "tst-dlmopen1mod.so");
xdlclose (h);
return 0;
}
#include <support/test-driver.c>

4
include/link.h
View File

@ -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

12
sysdeps/generic/ldsodefs.h
View File

@ -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;
@ -1099,12 +1099,16 @@ 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' for the namespace NS. LDBASE
is the run-time load address of the dynamic linker, to be put in the
`r_ldbase' member. Return the address of the structure. */
extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
attribute_hidden;
/* Update the `r_map' member and return the address of `struct r_debug'
of the namespace NS. */
extern struct r_debug *_dl_debug_update (Lmid_t ns) attribute_hidden;
/* Initialize the basic data structure for the search paths. SOURCE
is either "LD_LIBRARY_PATH" or "--library-path".
GLIBC_HWCAPS_PREPEND adds additional glibc-hwcaps subdirectories to