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A module that names a shared library in DT_NEEDED now gets it loaded and its imports bound against it, rather than being refused. libelf_insert() does the loading, which is what dlopen() calls anyway: the library lands in the module registry like anything else, its exports come back through libelf_getsymbol() -- the same call dlsym() uses -- and a library named by two modules is loaded once. A bare name is looked for along LD_LIBRARY_PATH, where dlopen() looks for it. Undefined symbols resolve against the globally registered symbols first, then the modules this one depends on, then the table exec() supplied. Nothing here calls into dlfcn, because this loader is also the kernel's module loader, which has none. Each library becomes one of the module's dependencies[], and the dependency holds it in place of the reference libelf_insert() took. So a library loaded only for DT_NEEDED is kept by the modules that depend on it, and libelf_undepend() unloads it with the last of them; one that dlopen() or insmod also opened stays until that reference goes too. CONFIG_LIBC_ELF_MAXDEPEND bounds how many libraries a module may name, which is what it already meant. Six things had to be fixed to make it work, none of which a build shows. reldata was a file-scope global. Loading a library from inside libelf_relocatedyn() makes that function reentrant, so the nested load overwrote the outer one's relocation offsets and the module resumed binding with the library's DT_REL. It is now per call. A cross-object call needs the callee's data base, not the caller's. A symbol resolved from an FDPIC library comes back as a descriptor, and R_ARM_FUNCDESC_VALUE was treating it as a code address and pairing it with the importing module's GOT. It now copies both words, so the library runs with its own. An object with no imports has no PLT and so no DT_PLTGOT, but it still has a GOT and still has to be entered with it. Without the fallback its descriptors carried a data base of zero and the library read its globals through a null pointer. R_ARM_FUNCDESC, a pointer to a descriptor, wrapped a library's descriptor in a second one. It now stores the library's descriptor as it is. The flag that says a resolved value is a descriptor was set only for an import and never cleared, so the next relocation against a symbol of the module itself took that symbol for a descriptor too. It is cleared there. libelf_symname() was static, and reading a DT_NEEDED name needs it. A module with DT_NEEDED is refused where CONFIG_LIBC_ELF_MAXDEPEND is zero, since that is where the dependency logic is compiled out. A DT_NEEDED library is one shared instance, its data included, because the loader returns the object already in the registry. A module started with exec() is different: that path loads the module afresh each time, so two running instances have separate data while sharing one copy of the text. Built for mps3-an547:picostest with CONFIG_FDPIC both ways. Run on mps2-an500:xipfs under QEMU: fdpicxip solib loads libcounter.so by name out of DT_NEEDED, two instances share one pinned copy of its text, and the library is unloaded, and its pin given back, when the second one exits. A library also opened with dlopen() stays loaded after its DT_NEEDED user exits, and dlclose() unloads it. With CONFIG_ARCH_ADDRENV the program runs in its own address space, which a library libelf_insert() loads cannot reach, so DT_NEEDED is refused there as before. Assisted-by: Claude Code:claude-opus-5-5 Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>
385 lines
13 KiB
C
385 lines
13 KiB
C
/****************************************************************************
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* libs/libc/elf/elf.h
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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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#ifndef __LIBS_LIBC_LIBC_ELF_LIBC_ELF_H
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#define __LIBS_LIBC_LIBC_ELF_LIBC_ELF_H
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/addrenv.h>
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#include <nuttx/lib/elf.h>
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/****************************************************************************
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* Public Function Prototypes
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****************************************************************************/
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/****************************************************************************
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* Name: libelf_verifyheader
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*
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* Description:
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* Given the header from a possible ELF executable, verify that it is
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* an ELF executable.
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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****************************************************************************/
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int libelf_verifyheader(FAR const Elf_Ehdr *header);
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/****************************************************************************
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* Name: libelf_findsymtab
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*
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* Description:
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* Find the symbol table section.
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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****************************************************************************/
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int libelf_findsymtab(FAR struct mod_loadinfo_s *loadinfo);
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/****************************************************************************
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* Name: libelf_readsym
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*
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* Description:
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* Read the ELF symbol structure at the specified index into memory.
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*
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* Input Parameters:
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* loadinfo - Load state information
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* index - Symbol table index
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* sym - Location to return the table entry
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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****************************************************************************/
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int libelf_readsym(FAR struct mod_loadinfo_s *loadinfo, int index,
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FAR Elf_Sym *sym, FAR Elf_Shdr *shdr);
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/****************************************************************************
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* Name: libelf_symvalue
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*
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* Description:
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* Get the value of a symbol. The updated value of the symbol is returned
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* in the st_value field of the symbol table entry.
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*
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* Input Parameters:
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* modp - Module state information
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* loadinfo - Load state information
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* sym - Symbol table entry (value might be undefined)
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* sh_offset - Offset of strtab
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* exports - Pointer to the symbol table
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* nexports - Number of symbols in the symbol table*
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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* EINVAL - There is something inconsistent in the symbol table (should
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* only happen if the file is corrupted)
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* ENOSYS - Symbol lies in common
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* ESRCH - Symbol has no name
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* ENOENT - Symbol undefined and not provided via a symbol table
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*
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****************************************************************************/
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int libelf_symvalue(FAR struct module_s *modp,
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FAR struct mod_loadinfo_s *loadinfo, FAR Elf_Sym *sym,
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Elf_Off sh_offset,
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FAR const struct symtab_s *exports, int nexports);
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/****************************************************************************
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* Name: libelf_insertsymtab
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*
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* Description:
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* Insert a symbol table for the current module.
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*
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* Input Parameters:
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* modp - Module state information
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* loadinfo - Module load information
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* shdr - Symbol table section header
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* sym - Symbol table entry
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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* ENOMEM - Symbol undefined and not provided via a symbol table
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*
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****************************************************************************/
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int libelf_insertsymtab(FAR struct module_s *modp,
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FAR struct mod_loadinfo_s *loadinfo,
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FAR Elf_Shdr *shdr,
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FAR Elf_Sym *sym);
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/****************************************************************************
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* Name: libelf_findglobal
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*
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* Description:
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* Find a symbol in the global symbol table
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*
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* Input Parameters:
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* modp - Module state information
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* loadinfo - Module load information
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* shdr - Symbol table section header
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* sym - Symbol table entry
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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* ENOMEM - Symbol undefined and not provided via a symbol table
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*
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****************************************************************************/
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void *libelf_findglobal(FAR struct module_s *modp,
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FAR struct mod_loadinfo_s *loadinfo,
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FAR Elf_Shdr *shdr,
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FAR Elf_Sym *sym);
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/****************************************************************************
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* Name: libelf_loadhdrs
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*
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* Description:
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* Loads program and section headers into memory.
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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****************************************************************************/
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int libelf_loadhdrs(FAR struct mod_loadinfo_s *loadinfo);
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/****************************************************************************
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* Name: libelf_sectname
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*
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* Description:
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* Get the symbol name in loadinfo->iobuffer[].
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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****************************************************************************/
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int libelf_sectname(FAR struct mod_loadinfo_s *loadinfo,
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FAR const Elf_Shdr *shdr);
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/****************************************************************************
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* Name: libelf_allocbuffer
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*
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* Description:
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* Perform the initial allocation of the I/O buffer, if it has not already
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* been allocated.
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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****************************************************************************/
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int libelf_allocbuffer(FAR struct mod_loadinfo_s *loadinfo);
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/****************************************************************************
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* Name: libelf_reallocbuffer
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*
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* Description:
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* Increase the size of I/O buffer by the specified buffer increment.
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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****************************************************************************/
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int libelf_reallocbuffer(FAR struct mod_loadinfo_s *loadinfo,
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size_t increment);
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/****************************************************************************
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* Name: libelf_freebuffers
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*
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* Description:
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* Release all working buffers.
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*
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* Returned Value:
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* 0 (OK) is returned on success and a negated errno is returned on
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* failure.
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*
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****************************************************************************/
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int libelf_freebuffers(FAR struct mod_loadinfo_s *loadinfo);
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/****************************************************************************
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* Name: libelf_symname
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*
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* Description:
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* Read a name out of a string table into the I/O buffer.
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*
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****************************************************************************/
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int libelf_symname(FAR struct mod_loadinfo_s *loadinfo,
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FAR const Elf_Sym *sym, Elf_Off sh_offset);
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/****************************************************************************
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* Name: libelf_addr
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*
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* Description:
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* Translate a link-time address in a loaded object to the address it
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* occupies now. An address below the data segment's link-time base
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* belongs to text, anything at or above it to data.
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*
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* Input Parameters:
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* loadinfo - Load state information
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* vaddr - The link-time address to translate
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*
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* Returned Value:
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* The run-time address.
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*
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****************************************************************************/
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static inline uintptr_t libelf_addr(FAR struct mod_loadinfo_s *loadinfo,
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uintptr_t vaddr)
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{
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if (loadinfo->datasec != 0 && vaddr >= loadinfo->datasec)
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{
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return loadinfo->datastart + (vaddr - loadinfo->datasec);
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}
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return loadinfo->textalloc + vaddr;
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}
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#ifdef CONFIG_ARCH_ADDRENV
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/****************************************************************************
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* Name: libelf_addrenv_alloc
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*
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* Description:
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* Allocate memory for the ELF image (textalloc and datastart). If
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* CONFIG_ARCH_ADDRENV=n, textalloc will be allocated using kmm_zalloc()
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* and datastart will be a offset from textalloc. If
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* CONFIG_ARCH_ADDRENV=y, then textalloc and datastart will be allocated
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* using up_addrenv_create(). In either case, there will be a unique
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* instance of textalloc and datastart (and stack) for each instance of a
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* process.
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*
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* Input Parameters:
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* loadinfo - Load state information
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* textsize - The size (in bytes) of the .text address environment needed
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* for the ELF image (read/execute).
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* datasize - The size (in bytes) of the .bss/.data address environment
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* needed for the ELF image (read/write).
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*
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* Returned Value:
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* Zero (OK) on success; a negated errno value on failure.
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*
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****************************************************************************/
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int libelf_addrenv_alloc(FAR struct mod_loadinfo_s *loadinfo,
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size_t textsize, size_t datasize);
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/****************************************************************************
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* Name: libelf_addrenv_select
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*
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* Description:
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* Temporarily select the task's address environment.
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*
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* Input Parameters:
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* loadinfo - Load state information
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*
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* Returned Value:
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* Zero (OK) on success; a negated errno value on failure.
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*
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****************************************************************************/
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int libelf_addrenv_select(FAR struct mod_loadinfo_s *loadinfo);
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/****************************************************************************
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* Name: libelf_addrenv_restore
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*
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* Description:
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* Restore the address environment before libelf_addrenv_select() was
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* called.
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*
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* Input Parameters:
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* loadinfo - Load state information
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*
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* Returned Value:
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* Zero (OK) on success; a negated errno value on failure.
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*
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****************************************************************************/
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int libelf_addrenv_restore(FAR struct mod_loadinfo_s *loadinfo);
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/****************************************************************************
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* Name: libelf_addrenv_free
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*
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* Description:
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* Release the address environment previously created by
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* libelf_addrenv_alloc(). This function is called only under certain
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* error conditions after the module has been loaded but not yet started.
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* After the module has been started, the address environment will
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* automatically be freed when the module exits.
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*
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* Input Parameters:
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* loadinfo - Load state information
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*
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* Returned Value:
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* None.
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*
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****************************************************************************/
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void libelf_addrenv_free(FAR struct mod_loadinfo_s *loadinfo);
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#endif /* CONFIG_ARCH_ADDRENV */
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#ifdef HAVE_LIBC_ELF_PIN
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/****************************************************************************
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* Name: libelf_pinrelease
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*
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* Description:
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* Give back an XIP pin that the loader took, and the file that holds it.
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* Does nothing if the loader took no pin.
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*
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* Input Parameters:
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* pinfile - The held file. Cleared on return.
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*
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* Returned Value:
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* None.
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*
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****************************************************************************/
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void libelf_pinrelease(FAR struct file **pinfile);
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#endif
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#endif /* __LIBS_LIBC_LIBC_ELF_LIBC_ELF_H */
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