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Message-Id: <20210830173844.458727-1-hjl.tools@gmail.com>
Date: Mon, 30 Aug 2021 10:38:42 -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 0/2] Extend struct r_debug to support multiple namespaces
Changes in the v6 patch:
1. Add comments for dl-debug-compat-symbols.[o|os] usage.
Changes in the v5 patch:
1. Use struct r_debug as the base for struct r_debug_extended.
2. Keep _dl_debug_initialize return type.
Changes in the v4 patch:
1. Improve the empty namespace removal from the namespace linked list.
2. Check r_version == 0 for the unused namespace.
Changes in the v3 patch:
1. Remove the empty namespace from the namespace linked list.
2. Properly add the new namespace to the linked list.
Changes in the v2 patch:
1. Bump r_version to 2.
2. Don't add DT_DEBUGSZ.
3. Add struct r_debug_extended to extend struct r_debug.
4. Don't update the r_state field in the copy of _r_debug in executable
since it is not consumed by the program.
---
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.
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.
H.J. Lu (2):
Add declare_object_symbol_alias for assembly codes [BZ #28128]
Extend struct r_debug to support multiple namespaces
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/libc-symbols.h | 12 +++---
include/link.h | 4 ++
sysdeps/generic/ldsodefs.h | 8 ++--
16 files changed, 270 insertions(+), 44 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
--
2.31.1
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