[v7,0/1] Extend struct r_debug to support multiple namespaces

Message ID 20210907151507.2955460-1-hjl.tools@gmail.com
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  • Extend struct r_debug to support multiple namespaces
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Florian Weimer via Libc-alpha Sept. 7, 2021, 3:15 p.m.
Changes in the v7 patch:

1. Rewrite dl-debug-symbols.S and remove dl-debug-compat-symbols.c.
2. Bump r_version to 2 only when multiple namespaces are used.
3. Verify r_version == 1 without multiple namespaces.
4. Keep the empty (unused) namespace on the namespace linked list.
5. Use atomic_store_release to update r_version and r_next.
6. Add _dl_debug_update without adding the namespace to the namespace
linked list.

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 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 compatibility symbol, _r_debug, with size of struct r_debug,
as an alise of _r_debug_extended, for programs which reference _r_debug.

This fixes BZ #15971.

H.J. Lu (1):
  Extend struct r_debug to support multiple namespaces [BZ #15971]

 NEWS                            | 11 ++++-
 csu/Makefile                    |  3 ++
 csu/rtld-sizes.sym              |  6 +++
 elf/Makefile                    |  7 +++-
 elf/dl-close.c                  |  2 +-
 elf/dl-debug-symbols.S          | 37 +++++++++++++++++
 elf/dl-debug.c                  | 71 ++++++++++++++++++++++++---------
 elf/dl-load.c                   |  2 +-
 elf/dl-open.c                   | 10 ++---
 elf/dl-reloc-static-pie.c       |  2 +-
 elf/link.h                      | 36 ++++++++++++-----
 elf/rtld-debugger-interface.txt | 14 +++++++
 elf/rtld.c                      |  4 +-
 elf/tst-dlmopen4.c              | 68 +++++++++++++++++++++++++++++++
 elf/tst-dlopen-nodelete-reloc.c |  2 +
 include/link.h                  |  4 ++
 sysdeps/generic/ldsodefs.h      | 12 ++++--
 17 files changed, 245 insertions(+), 46 deletions(-)
 create mode 100644 csu/rtld-sizes.sym
 create mode 100644 elf/dl-debug-symbols.S
 create mode 100644 elf/tst-dlmopen4.c

-- 
2.31.1