From a93d9e03a31ec14405cb3a09aa95413b67067380 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Tue, 17 Aug 2021 19:35:48 -0700 Subject: 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 --- elf/link.h | 35 ++++++++++++++++++++++++++--------- 1 file changed, 26 insertions(+), 9 deletions(-) (limited to 'elf/link.h') diff --git a/elf/link.h b/elf/link.h index ff3a85c847..200d40c9c6 100644 --- a/elf/link.h +++ b/elf/link.h @@ -34,14 +34,13 @@ #include /* Defines __ELF_NATIVE_CLASS. */ #include -/* 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' -- cgit v1.2.3