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Extend struct r_debug to support multiple namespaces [BZ #15971]

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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 <fweimer@redhat.com>
This commit is contained in:
H.J. Lu
2021-08-17 19:35:48 -07:00
parent 885762aa31
commit a93d9e03a3
16 changed files with 258 additions and 46 deletions
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83
elf/dl-debug.c
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@@ -30,37 +30,80 @@ extern const int verify_link_map_members[(VERIFY_MEMBER (l_addr)
&& VERIFY_MEMBER (l_prev))
? 1 : -1];
/* This structure communicates dl state to the debugger. The debugger
normally finds it via the DT_DEBUG entry in the dynamic section, but in
a statically-linked program there is no dynamic section for the debugger
to examine and it looks for this particular symbol name. */
struct r_debug _r_debug;
/* Update the `r_map' member and return the address of `struct r_debug'
of the namespace NS. */
struct r_debug *
_dl_debug_update (Lmid_t ns)
{
struct r_debug_extended *r;
if (ns == LM_ID_BASE)
r = &_r_debug_extended;
else
r = &GL(dl_ns)[ns]._ns_debug;
if (r->base.r_map == NULL)
atomic_store_release (&r->base.r_map,
(void *) GL(dl_ns)[ns]._ns_loaded);
return &r->base;
}
/* 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. */
/* Initialize _r_debug_extended for the namespace NS. LDBASE is the
run-time load address of the dynamic linker, to be put in
_r_debug_extended.r_ldbase. Return the address of _r_debug. */
struct r_debug *
_dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
{
struct r_debug *r;
struct r_debug_extended *r, **pp = NULL;
if (ns == LM_ID_BASE)
r = &_r_debug;
else
r = &GL(dl_ns)[ns]._ns_debug;
if (r->r_map == NULL || ldbase != 0)
{
/* 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_map = (void *) GL(dl_ns)[ns]._ns_loaded;
r->r_brk = (ElfW(Addr)) &_dl_debug_state;
r = &_r_debug_extended;
/* Initialize r_version to 1. */
if (_r_debug_extended.base.r_version == 0)
_r_debug_extended.base.r_version = 1;
}
else if (DL_NNS > 1)
{
r = &GL(dl_ns)[ns]._ns_debug;
if (r->base.r_brk == 0)
{
/* Add the new namespace to the linked list. After a namespace
is initialized, r_brk becomes non-zero. A namespace becomes
empty (r_map == NULL) when it is unused. But it is never
removed from the linked list. */
struct r_debug_extended *p;
for (pp = &_r_debug_extended.r_next;
(p = *pp) != NULL;
pp = &p->r_next)
;
r->base.r_version = 2;
}
}
return r;
if (r->base.r_brk == 0)
{
/* Tell the debugger where to find the map of loaded objects.
This function is called from dlopen. Initialize the namespace
only once. */
r->base.r_ldbase = ldbase ?: _r_debug_extended.base.r_ldbase;
r->base.r_brk = (ElfW(Addr)) &_dl_debug_state;
r->r_next = NULL;
}
if (r->base.r_map == NULL)
atomic_store_release (&r->base.r_map,
(void *) GL(dl_ns)[ns]._ns_loaded);
if (pp != NULL)
{
atomic_store_release (pp, r);
/* Bump r_version to 2 for the new namespace. */
atomic_store_release (&_r_debug_extended.base.r_version, 2);
}
return &r->base;
}