* [PATCH v2 2/2] ld.so: Hide _r_debug to support DT_DEBUG [BZ #28130]
@ 2021-08-02 20:42 H.J. Lu via Libc-alpha
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From: H.J. Lu via Libc-alpha @ 2021-08-02 20:42 UTC (permalink / raw)
To: libc-alpha
<link.h> has
extern struct r_debug _r_debug;
which is exported from ld.so. rtld.c has
/* Initialize _r_debug. */
struct r_debug *r = _dl_debug_initialize (GL(dl_rtld_map).l_addr,
LM_ID_BASE);
...
if (main_map->l_info[DT_DEBUG] != NULL)
/* There is a DT_DEBUG entry in the dynamic section. Fill it in
with the run-time address of the r_debug structure */
main_map->l_info[DT_DEBUG]->d_un.d_ptr = (ElfW(Addr)) r;
With COPY relocation, the address of _r_debug at run-time may be in the
executable if it references _r_debug. Since debugger uses DT_DEBUG, it
will reference the staled original definition of _r_debug in ld.so.
1. Make _r_debug a compatible symbol in ld.so and don't export it. The
existing dynamic executables with _r_debug reference will get a copy of
_r_debug which won't be updated by ld.so. But DT_DEBUG will work with
debuggers.
2. Make a hidden alias of _r_debug, _r_debug_internal, and use it in
ld.so.
3. Add a support function, get_r_debug, to return the value in DT_DEBUG,
which is the address of _r_debug. FIXME: MIPS needs to check a different
dynamic tag to get the address of _r_debug.
4. Provide
struct r_debug *get_r_debug (void);
#define _r_debug (*get_r_debug ())
in <support/support.h> to support glibc tests.
This fixes BZ #28130.
---
elf/Makefile | 2 ++
elf/circleload1.c | 1 +
elf/dl-debug.c | 28 ++++++++++++++---
elf/link.h | 3 --
elf/loadtest.c | 1 +
elf/neededtest.c | 1 +
elf/neededtest2.c | 1 +
elf/neededtest3.c | 1 +
elf/neededtest4.c | 1 +
elf/unload.c | 1 +
elf/unload2.c | 1 +
support/Makefile | 1 +
support/get_r_debug.c | 54 ++++++++++++++++++++++++++++++++
support/support.h | 6 ++++
sysdeps/generic/dl-get_r_debug.h | 28 +++++++++++++++++
15 files changed, 122 insertions(+), 8 deletions(-)
create mode 100644 support/get_r_debug.c
create mode 100644 sysdeps/generic/dl-get_r_debug.h
diff --git a/elf/Makefile b/elf/Makefile
index d05f410592..a4d3db922b 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -609,6 +609,8 @@ $(objpfx)ld.so: $(objpfx)librtld.os $(ld-map)
$(call after-link,$@.new)
$(READELF) -s $@.new \
| $(AWK) '($$7 ~ /^UND(|EF)$$/ && $$1 != "0:" && $$4 != "REGISTER") { print; p=1 } END { exit p != 0 }'
+ $(READELF) -rW $@.new \
+ | $(AWK) '($$5 ~/_r_debug/) { print; p=1 } END { exit p != 0 }'
mv -f $@.new $@
ifeq (yes,$(build-shared))
diff --git a/elf/circleload1.c b/elf/circleload1.c
index 990ff84a84..e1ff8e272b 100644
--- a/elf/circleload1.c
+++ b/elf/circleload1.c
@@ -4,6 +4,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
+#include <support/support.h>
#define MAPS ((struct link_map *) _r_debug.r_map)
diff --git a/elf/dl-debug.c b/elf/dl-debug.c
index 2cd5f09753..a70ba7abb7 100644
--- a/elf/dl-debug.c
+++ b/elf/dl-debug.c
@@ -17,7 +17,7 @@
<https://www.gnu.org/licenses/>. */
#include <ldsodefs.h>
-
+#include <shlib-compat.h>
/* These are the members in the public `struct link_map' type.
Sanity check that the internal type and the public type match. */
@@ -36,9 +36,27 @@ extern const int verify_link_map_members[(VERIFY_MEMBER (l_addr)
to examine and it looks for this particular symbol name. */
struct r_debug _r_debug;
+extern struct r_debug _r_debug_internal attribute_hidden;
+strong_alias (_r_debug, _r_debug_internal)
+
+/* Define ABI_rtld_GLIBC_2_35 from ABI_rtld_GLIBC_2_34 if there are no
+ symbols in GLIBC_2.35 when this macro was first used. */
+#ifndef ABI_rtld_GLIBC_2_35
+# define ABI_rtld_GLIBC_2_35 ABI_rtld_GLIBC_2_34
+#endif
+
+/* The latest ABI of _r_debug is GLIBC_2.33 in RV32 of RISC-V. */
+#if ABI_rtld_GLIBC_2_35 != ABI_rtld_GLIBC_2_34
+# error ABI_rtld_GLIBC_2_35 != ABI_rtld_GLIBC_2_34
+#endif
+
+#if SHLIB_COMPAT (rtld, GLIBC_2_0, GLIBC_2_35)
+strong_alias (_r_debug, _r_debug_compat)
+compat_symbol (rtld, _r_debug_compat, _r_debug, GLIBC_2_0);
+#endif
-/* 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
+/* 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. */
struct r_debug *
@@ -47,7 +65,7 @@ _dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
struct r_debug *r;
if (ns == LM_ID_BASE)
- r = &_r_debug;
+ r = &_r_debug_internal;
else
r = &GL(dl_ns)[ns]._ns_debug;
@@ -55,7 +73,7 @@ _dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
{
/* 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_ldbase = ldbase ?: _r_debug_internal.r_ldbase;
r->r_map = (void *) GL(dl_ns)[ns]._ns_loaded;
r->r_brk = (ElfW(Addr)) &_dl_debug_state;
}
diff --git a/elf/link.h b/elf/link.h
index ff3a85c847..3431142d10 100644
--- a/elf/link.h
+++ b/elf/link.h
@@ -63,9 +63,6 @@ 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. */
-extern struct r_debug _r_debug;
-
/* 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:
diff --git a/elf/loadtest.c b/elf/loadtest.c
index b5eab5e93c..9c507e8802 100644
--- a/elf/loadtest.c
+++ b/elf/loadtest.c
@@ -6,6 +6,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
+#include <support/support.h>
/* How many load/unload operations do we do. */
diff --git a/elf/neededtest.c b/elf/neededtest.c
index 3cea499314..252e193dca 100644
--- a/elf/neededtest.c
+++ b/elf/neededtest.c
@@ -4,6 +4,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
+#include <support/support.h>
#define MAPS ((struct link_map *) _r_debug.r_map)
diff --git a/elf/neededtest2.c b/elf/neededtest2.c
index 17c75f2ba3..129c2ac486 100644
--- a/elf/neededtest2.c
+++ b/elf/neededtest2.c
@@ -4,6 +4,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
+#include <support/support.h>
#define MAPS ((struct link_map *) _r_debug.r_map)
diff --git a/elf/neededtest3.c b/elf/neededtest3.c
index 41970cf2c7..5f6940fcbe 100644
--- a/elf/neededtest3.c
+++ b/elf/neededtest3.c
@@ -4,6 +4,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
+#include <support/support.h>
#define MAPS ((struct link_map *) _r_debug.r_map)
diff --git a/elf/neededtest4.c b/elf/neededtest4.c
index 0ae0b7ff47..50a88e8835 100644
--- a/elf/neededtest4.c
+++ b/elf/neededtest4.c
@@ -4,6 +4,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
+#include <support/support.h>
#define MAPS ((struct link_map *) _r_debug.r_map)
diff --git a/elf/unload.c b/elf/unload.c
index 4566f226f8..35c8a03f79 100644
--- a/elf/unload.c
+++ b/elf/unload.c
@@ -8,6 +8,7 @@
#include <mcheck.h>
#include <stdio.h>
#include <stdlib.h>
+#include <support/support.h>
#define MAPS ((struct link_map *) _r_debug.r_map)
diff --git a/elf/unload2.c b/elf/unload2.c
index eef2bfd426..9e8b26ec55 100644
--- a/elf/unload2.c
+++ b/elf/unload2.c
@@ -5,6 +5,7 @@
#include <link.h>
#include <stdio.h>
#include <stdlib.h>
+#include <support/support.h>
#define MAPS ((struct link_map *) _r_debug.r_map)
diff --git a/support/Makefile b/support/Makefile
index a462781718..5b6d5bb23a 100644
--- a/support/Makefile
+++ b/support/Makefile
@@ -32,6 +32,7 @@ libsupport-routines = \
check_hostent \
check_netent \
delayed_exit \
+ get_r_debug \
ignore_stderr \
next_to_fault \
oom_error \
diff --git a/support/get_r_debug.c b/support/get_r_debug.c
new file mode 100644
index 0000000000..2bc30022fe
--- /dev/null
+++ b/support/get_r_debug.c
@@ -0,0 +1,54 @@
+/* Return a pointer to _r_debug, the internal debug structure in the
+ dynamic linker.
+ 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>
+#include <dl-get_r_debug.h>
+
+/* Get a pointer to _r_debug. */
+
+static int
+callback (struct dl_phdr_info *info, size_t size, void *data)
+{
+ const ElfW(Phdr) *phdr = info->dlpi_phdr;
+ ElfW(Dyn) *d;
+ int n;
+ struct r_debug **debugp = (struct r_debug **) data;
+
+ for (n = info->dlpi_phnum; --n >= 0; phdr++)
+ if (phdr->p_type == PT_DYNAMIC)
+ {
+ d = (void *) (info->dlpi_addr + phdr->p_vaddr);
+ struct r_debug *debug = dl_get_r_debug (d);
+ if (debug != NULL)
+ {
+ *debugp = debug;
+ return 1;
+ }
+ }
+
+ return 0;
+}
+
+struct r_debug *
+get_r_debug (void)
+{
+ struct r_debug *debug = NULL;
+ dl_iterate_phdr (callback, &debug);
+ return debug;
+}
diff --git a/support/support.h b/support/support.h
index 834dba9097..6d00e4c46e 100644
--- a/support/support.h
+++ b/support/support.h
@@ -33,6 +33,8 @@
#include <sys/types.h>
/* For locale_t. */
#include <locale.h>
+/* For struct r_debug. */
+#include <link.h>
__BEGIN_DECLS
@@ -193,6 +195,10 @@ struct support_stack support_stack_alloc (size_t size);
/* Deallocate the STACK. */
void support_stack_free (struct support_stack *stack);
+/* Get a pointer to _r_debug. */
+struct r_debug *get_r_debug (void);
+#define _r_debug (*get_r_debug ())
+
__END_DECLS
#endif /* SUPPORT_H */
diff --git a/sysdeps/generic/dl-get_r_debug.h b/sysdeps/generic/dl-get_r_debug.h
new file mode 100644
index 0000000000..2595ec2ba9
--- /dev/null
+++ b/sysdeps/generic/dl-get_r_debug.h
@@ -0,0 +1,28 @@
+/* Get a pointer to _r_debug from PT_DYNAMIC.
+ 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/>. */
+
+/* Return the value in DT_DEBUG. */
+
+struct r_debug *
+dl_get_r_debug (ElfW(Dyn) *d)
+{
+ for (; d->d_tag != DT_NULL; ++d)
+ if (d->d_tag == DT_DEBUG)
+ return (struct r_debug *) d->d_un.d_val;
+ return NULL;
+}
--
2.31.1
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2021-08-02 20:42 [PATCH v2 2/2] ld.so: Hide _r_debug to support DT_DEBUG [BZ #28130] H.J. Lu via Libc-alpha
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