Setting the LD_DUMP_REL_PRE or LD_DUMP_REL_POST environment variables
cause rtld-elf to output a table of all relocations.
This is useful for debugging.
While I'm here:
- Let lm_add() call strdup() on its own behalf.
- Use a temporary pointer when parsing constraints; only set the
constraint pointer on a totally successful match.
PR: bin/52783
Submitted by: David P. Reese Jr. <daver@gomerbud.com>
Approved by: re (rwatson)
implementation in case default one provided by rtld is
not suitable.
Consolidate various identical MD lock implementation into
a single file using appropriate machine/atomic.h.
Approved by: re (scottl)
DT_NEEDED links is not flexible enough for cases where dynamically
loaded modules form a dependency cycle.
This should fix an infinite recursion problem encountered by Yahoo.
Approved by: re (jhb)
This is an optional feature, disabled by default.
This will be useful to people testing the various POSIX threading
libraries under -CURRENT but can easily serve other needs.
objects.
Programs such as sshd depend on two pointers to the same function being
equal in a given process. However, the current ia64 implementation
ensures that they're equal when both the pointers are instantiated in
the same ELF object. The attached patch ensures that they're equal
irrespective of where they're instantiated.
Reviewed by marcel@ (mentor) and kan@
Introduce a new unlink_object() function and call it in
unload_object() instead. Removing the object in unref_dag() is
too early, rtld calls _fini() function after that and shared
objects might fail resolve their own symbols.
Introdice RTLD_SELF special handle and properly process it within
dlsym() and dlinfo() functions.
The intention is to improve our compatibility with Solaris and
to make a Java port easier.
Partially submitted by: phantom
associated lists:
remove RTLD_GLOBAL objects from global objects list;
remove the parent object from dldags list of its children.
Previosly we were doing that only to the top-level object OF the DAG
being unloaded and all its dependencies were ignored, leading to
mysterious crashes later.
Submitted by: peter (partially)
skipping read-only pages, which can result in valuable non-text-related
data not getting dumped, the ELF loader and the dynamic loader now mark
read-only text pages NOCORE and the coredump code only checks (primarily) for
complete inaccessibility of the page or NOCORE being set.
Certain applications which map large amounts of read-only data will
produce much larger cores. A new sysctl has been added,
debug.elf_legacy_coredump, which will revert to the old behavior.
This commit represents collaborative work by all parties involved.
The PR contains a program demonstrating the problem.
PR: kern/45994
Submitted by: "Peter Edwards" <pmedwards@eircom.net>, Archie Cobbs <archie@dellroad.org>
Reviewed by: jdp, dillon
MFC after: 7 days
before referencing object's DAG. This makes it possible for
C++ exceptions to work across shared libraries and brings
us closer to the search order used by Solaris/Linux.
Reviewed by: jdp
Approved by: obrien
MFC after: 1 month
even if there was no error occured (when trying to dlopen(3) object that
already linked into executable which does dlopen(3) call). This is more
proper fix for `ldd /usr/lib/libc.so' problem, because the new behaviour
conforms to documentation.
Remove workaround from ldd.c (rev.1.32).
PR: 35099
Submitted by: Nathan Hawkins <utsl@quic.net>
MFC after: 1 week
for the DT_IA64_PLT_RESERVE dynamic table entry. When a shared object
does not have any PLT relocations, the linker apparently doesn't find
it necessary to actually reserve the space for the BOR (Bind On
Reference) entries as pointed to by the DTE. As a result, relocatable
data in the PLT was overwritten, causing some unexpected control flow
with annoyingly predictable outcome: coredump.
To reproduce:
% echo 'int main() { return 0; }' > foo.c
% cc -o foo foo.c -lxpg4
objects' reference counts. This function is called by the atexit
mechanism at program shutdown. I don't think the locking is necessary
here. It caused OpenOffice builds to hang more often than not.
Credit to Martin Blapp and Matt Dillon for helping to diagnose this
problem and for testing the fix.
They provided little benefit (if any) and they caused some problems
in OpenOffice, at least in post-KSE -current and perhaps in other
environments too. The nanosleep calls prevented the profiling timer
from advancing during the spinloops, thereby preventing the thread
scheduler from ever pre-empting the spinning thread. Alexander
Kabaev diagnosed this problem, Martin Blapp helped with testing,
and Matt Dillon provided some helpful suggestions.
This is a short-term fix for a larger problem. The use of spinlocking
isn't guaranteed to work in all cases. For example, if the spinning
thread has higher priority than all other threads, it may never be
pre-empted, and the thread holding the lock may never progress far
enough to release the lock. On the other hand, spinlocking is the
only locking that can work with an arbitrary unknown threads package.
I have some ideas for a much better fix in the longer term. It
would eliminate all locking inside the dynamic linker by making it
safe for symbol lookups and lazy binding to proceed in parallel
with a call to dlopen or dlclose. This means that the only mutual
exclusion needed would be to prevent multiple simultaneous calls
to dlopen and/or dlclose. That mutual exclusion could be put into
the native pthreads library. Applications using foreign threads
packages would have to make their own arrangements to ensure that
they did not have multiple threads in dlopen and/or dlclose -- a
reasonable requirement in my opinion.
MFC after: 3 days
matching constraints where appropriate. This makes the dynamic
linker buildable at -O0 again.
Thanks to Bruce Evans for identifying the cause of the build
problem.
MFC after: 1 week
Untested (testing request went unanswered), but sparc64 is not expected to
cause problems. IA64 is not expected to cause problems but the patch was
slightly more complex so the possibility exists.
Approved by: jdp
goto target was so the cache could be freed. So free the cache after
done: rather then before done: (!)
Submitted by: Gavin Atkinson <gavin@ury.york.ac.uk>
Martin Blapp determined that the elf dynamic loader was at fault. In
particular, the loader uses alloca() to allocate a symbol cache on the
stack. Normally this would work just fine, but if the loader is called
from a threaded program and the object being loaded is fairly large the
alloca() can blow away the thread stack and effect other nearby thread
stacks as well. My testing showed that the symbol cache can be as large
as 250KBytes during the openoffice port build and install sequence. Martin
was able to work around the problem by disabling the symbol cache
(cache = NULL;). However, this solution is not adequate for commit because
it can cause an enormous cpu burden for applications which do a lot of
dynamic loading (e.g. like konqueror).
The solution is to use anonymous mmap() to temporarily allocate space to
hold the symbol cache. In testing I found that replacing the alloca()
with mmap() has no observable degredation in performance.
It should be noted that this bug does not necessarily cause an immediate
crash but can instead result in long term corruption and instability in
applications that load modules from threads. The bug is almost certainly
responsible for some of the instabilities found in konqueror, for example,
and possibly netscape too.
Sleuthing work by: Martin Blapp <mb@imp.ch>
X-MFC after: Before or after the 4.6 release depending on the release engineers
o Set st_shndx for sym_zero to SHN_UNDEF instead of SHN_ABS.
This gives us something to reliably test against.
o For weak references to undefined sysmbols (as indicated by
having st_shndx equals SHN_UNDEF) in the context of OPDs,
the address of the OPD is to be zero, not the address of
the function it contains.
o For weak references to undefined symbols in all other cases
(only DIR64LSB at this time), the actual relocated value is
to be zero, not the value prior to relocating.
Roughly speaking, weak references to undefined symbols are no-ops.
Tested on: i386, ia64
relocation identifies the symbol to which we need to bind. This
solves a problem seen on ia64 where the symbol hash table does not
contain local symbols and thus resulted in unresolved symbols.
Tested on: alpha, i386, ia64
objects were not being correctly set to zero. Instead, the function
descriptor pointer was set to the load address of the .so object. This
caused gcc generated binaries to segfault on exit when crtbegin.asm's
_fini code tested the __cxa_finalize() function pointer for zero.
This is a bit of a hack because of a problem nearby workaround for
find_symdef and its quirks (failures) for local symbols. This still
needs to be fixed.
produced by ld(8) (ie: that _DYNAMIC immediately follows the _GOT).
The new binutils import changed that, and the intial GOT relocation
broke. Use a custom linker script to provide a real end-of-GOT symbol.
Update ld.so to deal with the new (faster) PLT format that gcc-3.1 and
binutils can produce.
This is probably incomplete, but appears to be working again.
Obtained from: NetBSD
(And a fix to a silly mistake that I made by: gallatin)
and sbrk's prototype from char *sbrk(int) to void *sbrk(intptr_t).
This makes us more consistant with NetBSD and standards which include
these functions. Bruce pointed out that ptrdiff_t would probably
have been better than intptr_t, but this doesn't match other
implimentations.
Also remove local declarations of sbrk and unnecessary casting.
PR: 32296
Tested by: Harti Brandt <brandt@fokus.gmd.de>
MFC after: 1 month
DT_INIT and DT_FINI tags pointed to fptr records. In 2.11.2, it points
to the actuall address of the function. On IA64 you cannot just take
an address of a function, store it in a function pointer variable and
call it.. the function pointers point to a fptr data block that has the
target gp and address in it. This is absolutely necessary for using
the in-tree binutils toolchain, but (unfortunately) will not work with
old shared libraries. Save your old ld-elf.so.1 if you want to use
old ones still. Do not mix-and-match.
This is a no-op change for i386 and alpha.
Reviewed by: dfr
Avoid using parenthesis enclosure macros (.Pq and .Po/.Pc) with plain text.
Not only this slows down the mdoc(7) processing significantly, but it also
has an undesired (in this case) effect of disabling hyphenation within the
entire enclosed block.
particularly help programs which load many shared libraries with
a lot of relocations. Large C++ programs such as are found in KDE
are a prime example.
While relocating a shared object, maintain a vector of symbols
which have already been looked up, directly indexed by symbol
number. Typically, symbols which are referenced by a relocation
entry are referenced by many of them. This is the same optimization
I made to the a.out dynamic linker in 1995 (rtld.c revision 1.30).
Also, compare the first character of a sought-after symbol with its
symbol table entry before calling strcmp().
On a PII/400 these changes reduce the start-up time of a typical
KDE program from 833 msec (elapsed) to 370 msec.
MFC after: 5 days
longer includes machine/elf.h.
* consumers of elf.h now use the minimalist elf header possible.
This change is motivated by Binutils 2.11.0 and too much clashing over
our base elf headers and the Binutils elf headers.
The function's callers generate the error message when appropriate.
This eliminates the message ``Undefined symbol "__register_frame_info"''
which was bogusly returned by dlerror() in some cases.
function, thus allowing a debugger or other trace tool
to easily grab the addresses of the needed structures
off the stack.
This change is transparent to gdb, which locates the
link_map list and transfers it to debugger memory
for comparison purposes.
A sample program will be committed showing how this can
be used.
Reviewed by: John Polstra <jdp@FreeBSD.org>
Formerly the init functions were called in the opposite of the
order in which libraries were loaded, and libraries were loaded
according to a breadth-first traversal of the dependency graph.
That ordering came from SVR4.0, and it was easy to implement but
not always sensible.
Now we do a depth-first walk over the dependency graph and call
the init functions in an order such that each shared object's needed
objects are initialized before the shared object itself. At the
same time we build a list of finalization (fini) functions in the
opposite order, to guarantee correct C++ destructor ordering whenever
possible. (It may not be possible if dlopen and dlclose are used
in strange ways, but we come as close as one can come.)
The need for this renovation has become apparent as more programs
have started using multithreading. The multithreaded C library
libc_r requires initialization, whereas the standard libc does not.
Since virtually every other object depends on the C library, it is
important that it get initialized first.
lock against themselves, causing infinite spinning. Brian Feldman
found this problem when testing with Mozilla and supplied the fix,
which I have revised slightly.
Here is the failure scenario. A thread calls dlopen() and acquires
the writer lock. While the thread still holds the lock, a signal
is delivered and caught. The signal handler tries to call a function
which hasn't been bound yet. It thus enters the dynamic linker
and tries to acquire the reader lock. Since the writer lock is
already held, it will spin forever in the signal handler. The
thread holding the lock won't be able to progress and release the
lock.
The solution is to block almost all signals while holding the
exclusive lock.
A similar problem could conceivably occur in the opposite order.
Namely, a thread is holding the reader lock and then a signal
handler calls dlopen() or dlclose() and spins waiting for the writer
lock. We deal with this administratively by proclaiming that signal
handlers aren't allowed to call dlopen() or dlclose(). Actually
we don't have to proclaim a thing, since signal handlers aren't
allowed to call any system functions except those which are explicitly
permitted.
Submitted by: Brian Fundakowski Feldman <green>
