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e47be608d5
dlopen() of a library that is already loaded fails. libelf_insert() rejects a name that is already in the module registry with EEXIST, and dlinsert() passes that straight out, so the second caller gets NULL. POSIX says dlopen() shall return a handle to the object, and there is no way today for two modules to hold the same library at once -- which is what a shared library is for. So dlopen() now takes another reference on a library that is already there, and dlclose() only tears it down when the last handle goes. The count lives in the dlfcn layer rather than in libelf_insert() so that insmod keeps its own behaviour: a second insmod of the same name still fails with EEXIST, which is right for a kernel module. The module name is what makes any of this possible, and a PROTECTED build did not have one. Names were defined for CONFIG_BUILD_FLAT or the kernel side of a split build, on the reasoning that only the kernel needed them, which predates dlopen() being usable from user space. Without a name the user-space copy of libelf cannot recognise a second open of a library, cannot count opens, and cannot make dlclose() mean anything -- two dlopen()s there produce two independent copies of the library and lose track of the first. Names are therefore defined wherever CONFIG_LIBC_DLFCN is, which costs NAME_MAX per loaded module in that configuration. The path no longer has to be copied either. The module name is the basename of the file and libelf_insert() takes it as a const string, so dlinsert() finds it with strrchr() instead of handing a writable duplicate of the whole path to basename(). BUILD_KERNEL is deliberately untouched. dlopen() returns NULL there unconditionally: dlinsert() is a stub, because sharing a library between processes with separate address spaces needs the text in a shared region and the data per process at a matching virtual address, which is a different problem from this one. Built for mps3-an547:picostest with and without CONFIG_LIBC_DLFCN, and for stm32f4discovery:kostest, a PROTECTED configuration, with it enabled. Assisted-by: Claude Opus 5 (1M context) <noreply@anthropic.com> Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>
117 lines
4.9 KiB
C
117 lines
4.9 KiB
C
/****************************************************************************
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* libs/libc/dlfcn/lib_dlclose.c
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <dlfcn.h>
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#include <nuttx/lib/elf.h>
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: dlclose
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*
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* Description:
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* dlclose() is used to inform the system that the object referenced by a
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* handle returned from a previous dlopen() invocation is no longer needed
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* by the application.
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*
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* The use of dlclose() reflects a statement of intent on the part of the
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* process, but does not create any requirement upon the implementation,
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* such as removal of the code or symbols referenced by handle. Once an
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* object has been closed using dlclose() an application should assume
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* that its symbols are no longer available to dlsym(). All objects loaded
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* automatically as a result of invoking dlopen() on the referenced object
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* are also closed.
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*
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* Although a dlclose() operation is not required to remove structures
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* from an address space, neither is an implementation prohibited from
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* doing so. The only restriction on such a removal is that no object will
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* be removed to which references have been relocated, until or unless all
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* such references are removed. For instance, an object that had been
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* loaded with a dlopen() operation specifying the RTLD_GLOBAL flag might
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* provide a target for dynamic relocations performed in the processing of
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* other objects - in such environments, an application may assume that no
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* relocation, once made, will be undone or remade unless the object
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* requiring the relocation has itself been removed.
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*
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* Input Parameters:
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* handle - The opaque, non-NULL value returned by a previous successful
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* call to dlopen().
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*
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* Returned Value:
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* If the referenced object was successfully closed, dlclose() returns 0.
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* If the object could not be closed, or if handle does not refer to an
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* open object, dlclose() returns a non-zero value. More detailed
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* diagnostic information will be available through dlerror().
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*
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* Reference: OpenGroup.org
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*
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****************************************************************************/
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int dlclose(FAR void *handle)
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{
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#if defined(CONFIG_BUILD_FLAT) || defined(CONFIG_BUILD_PROTECTED)
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/* In the FLAT build, a shared library is essentially the same as a kernel
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* module.
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*
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* The PROTECTED build is equivalent to the FLAT build EXCEPT that there
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* must be two copies of the module logic: One residing in kernel
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* space and using the kernel symbol table and one residing in user space
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* using the user space symbol table.
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*
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* dlremove() is essentially a clone of rmmod().
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*/
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/* libelf_remove() gives back a reference and unloads only when the last
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* one goes, so closing one of two handles leaves the other usable.
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*/
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return libelf_remove(handle);
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#else /* if defined(CONFIG_BUILD_KERNEL) */
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/* The KERNEL build is considerably more complex: In order to be shared,
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* the .text portion of the module must be (1) build for PIC/PID operation
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* and (2) must like in a shared memory region accessible from all
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* processes. The .data/.bss portion of the module must be allocated in
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* the user space of each process, but must lie at the same virtual address
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* so that it can be referenced from the one copy of the text in the shared
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* memory region.
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*/
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/* #warning Missing logic */
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return -ENOSYS;
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#endif
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}
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