mbox series

[v6,0/2] Extend struct r_debug to support multiple namespaces

Message ID 20210830173844.458727-1-hjl.tools@gmail.com
Headers show
Series Extend struct r_debug to support multiple namespaces | expand

Message

H.J. Lu Aug. 30, 2021, 5:38 p.m. UTC
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