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/* vi: set sw=4 ts=4: */
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* A small little ldd implementation for uClibc
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* Copyright (C) 2000 by Lineo, inc.
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* Copyright (C) 2000,2001 Erik Andersen <andersee@debian.org>
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* Written by Erik Andersen <andersee@debian.org>
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* Several functions in this file (specifically, elf_find_section_type(),
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* elf_find_phdr_type(), and elf_find_dynamic(), were stolen from elflib.c from
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* elfvector (http://www.BitWagon.com/elfvector.html) by John F. Reiser
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* <jreiser@BitWagon.com>, which is copyright 2000 BitWagon Software LLC
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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#include <sys/types.h>
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struct library *lib_list = NULL;
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char not_found[] = "not found";
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Elf32_Shdr * elf_find_section_type( int key, Elf32_Ehdr *ehdr)
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Elf32_Shdr *shdr = (Elf32_Shdr *)(ehdr->e_shoff + (char *)ehdr);
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for (j = ehdr->e_shnum; --j>=0; ++shdr) {
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if (shdr->sh_type == key) {
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Elf32_Phdr * elf_find_phdr_type( int type, Elf32_Ehdr *ehdr)
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Elf32_Phdr *phdr = (Elf32_Phdr *)(ehdr->e_phoff + (char *)ehdr);
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for (j = ehdr->e_phnum; --j>=0; ++phdr) {
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if (type==phdr->p_type) {
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/* Returns value if return_val==1, ptr otherwise */
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void * elf_find_dynamic(int const key, Elf32_Dyn *dynp,
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Elf32_Ehdr *ehdr, int return_val)
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Elf32_Phdr *pt_text = elf_find_phdr_type(PT_LOAD, ehdr);
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unsigned tx_reloc = pt_text->p_vaddr - pt_text->p_offset;
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for (; DT_NULL!=dynp->d_tag; ++dynp) {
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if (dynp->d_tag == key) {
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return (void *)dynp->d_un.d_val;
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return (void *)(dynp->d_un.d_val - tx_reloc + (char *)ehdr );
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int check_elf_header(Elf32_Ehdr const *const ehdr)
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if (! ehdr || strncmp((void *)ehdr, ELFMAG, SELFMAG) != 0 ||
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ehdr->e_ident[EI_CLASS] != ELFCLASS32 ||
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ehdr->e_ident[EI_VERSION] != EV_CURRENT)
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/* This function's behavior must exactly match that
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* in uClibc/ldso/d-link/readelflib1.c */
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static void search_for_named_library(char *name, char *result, const char *path_list)
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struct stat filestat;
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/* We need a writable copy of this string */
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path = strdup(path_list);
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fprintf(stderr, "Out of memory!\n");
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/* Eliminate all double //s */
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while((path_n=strstr(path_n, "//"))) {
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memmove(path_n, path_n+1, i-1);
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/* Replace colons with zeros in path_list and count them */
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for(i=strlen(path); i > 0; i--) {
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for (i = 0; i < count; i++) {
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strcat(result, path_n);
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strcat(result, name);
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if (stat (result, &filestat) == 0 && filestat.st_mode & S_IRUSR) {
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path_n += (strlen(path_n) + 1);
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void locate_library_file(Elf32_Ehdr* ehdr, Elf32_Dyn* dynamic, char *strtab, int is_suid, struct library *lib)
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struct stat filestat;
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/* If this is a fully resolved name, our job is easy */
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if (stat (lib->name, &filestat) == 0) {
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lib->path = lib->name;
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/* We need some elbow room here. Make some room...*/
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fprintf(stderr, "Out of memory!\n");
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/* This function must match the behavior of _dl_load_shared_library
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* in readelflib1.c or things won't work out as expected... */
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/* The ABI specifies that RPATH is searched first, so do that now. */
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path = (char *)elf_find_dynamic(DT_RPATH, dynamic, ehdr, 0);
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search_for_named_library(lib->name, buf, path);
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/* Next check LD_{ELF_}LIBRARY_PATH if specified and allowed.
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* Since this app doesn't actually run an executable I will skip
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* the suid check, and just use LD_{ELF_}LIBRARY_PATH if set */
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path = getenv("LD_LIBRARY_PATH");
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search_for_named_library(lib->name, buf, path);
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/* FIXME -- add code to check the Cache here */
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/* Lastly, search the standard list of paths for the library.
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This list must exactly match the list in uClibc/ldso/d-link/readelflib1.c */
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path = UCLIBC_TARGET_PREFIX "/usr/lib:"
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UCLIBC_TARGET_PREFIX "/lib:"
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UCLIBC_DEVEL_PREFIX "/lib:"
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UCLIBC_BUILD_DIR "/lib:"
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search_for_named_library(lib->name, buf, path);
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lib->path = not_found;
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static int add_library(Elf32_Ehdr* ehdr, Elf32_Dyn* dynamic, char *strtab, int is_setuid, char *s)
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char *tmp, *tmp1, *tmp2;
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struct library *cur, *newlib=lib_list;
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if (!s || !strlen(s))
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/* We add libc.so.0 elsewhere */
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if (strcmp(s, UCLIBC_LDSO)==0)
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for (cur = lib_list; cur; cur=cur->next) {
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/* Check if this library is already in the list */
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tmp1 = tmp2 = cur->name;
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if(strcmp(tmp2, s)==0) {
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//printf("find_elf_interpreter is skipping '%s' (already in list)\n", cur->name);
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/* Ok, this lib needs to be added to the list */
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newlib = malloc(sizeof(struct library));
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newlib->name = malloc(strlen(s)+1);
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strcpy(newlib->name, s);
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newlib->resolved = 0;
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/* Now try and locate where this library might be living... */
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locate_library_file(ehdr, dynamic, strtab, is_setuid, newlib);
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//printf("add_library is adding '%s' to '%s'\n", newlib->name, newlib->path);
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for (cur = lib_list; cur->next; cur=cur->next); /* nothing */
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static void find_needed_libraries(Elf32_Ehdr* ehdr, Elf32_Dyn* dynamic, char *strtab, int is_setuid)
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for (dyns=dynamic; dyns->d_tag!=DT_NULL; ++dyns) {
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if (dyns->d_tag == DT_NEEDED) {
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add_library(ehdr, dynamic, strtab, is_setuid, (char*)strtab + dyns->d_un.d_val);
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static void find_elf_interpreter(Elf32_Ehdr* ehdr, Elf32_Dyn* dynamic, char *strtab, int is_setuid)
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static int been_there_done_that=0;
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if (been_there_done_that==1)
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been_there_done_that=1;
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phdr = elf_find_phdr_type(PT_INTERP, ehdr);
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struct library *cur, *newlib=NULL;
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char *s = (char*)ehdr + phdr->p_offset;
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for (cur = lib_list; cur; cur=cur->next) {
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/* Check if this library is already in the list */
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if(strcmp(cur->name, tmp1)==0) {
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//printf("find_elf_interpreter is replacing '%s' (already in list)\n", cur->name);
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newlib = malloc(sizeof(struct library));
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newlib->name = malloc(strlen(s)+1);
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strcpy(newlib->name, s);
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newlib->path = newlib->name;
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newlib->resolved = 1;
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//printf("find_elf_interpreter is adding '%s' to '%s'\n", newlib->name, newlib->path);
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for (cur = lib_list; cur->next; cur=cur->next); /* nothing */
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/* map the .so, and locate interesting pieces */
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int find_dependancies(char* filename)
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Elf32_Ehdr *ehdr = NULL;
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Elf32_Shdr *dynsec = NULL;
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Elf32_Dyn *dynamic = NULL;
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if (filename == not_found)
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fprintf(stderr, "No filename specified.\n");
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if (!(thefile = fopen(filename, "r"))) {
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if (fstat(fileno(thefile), &statbuf) < 0) {
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if (statbuf.st_size < sizeof(Elf32_Ehdr))
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/* mmap the file to make reading stuff from it effortless */
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ehdr = (Elf32_Ehdr *)mmap(0, statbuf.st_size,
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PROT_READ|PROT_WRITE, MAP_PRIVATE, fileno(thefile), 0);
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/* Check if this looks like a legit ELF file */
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if (check_elf_header(ehdr)) {
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fprintf(stderr, "%s: not an ELF file.\n", filename);
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/* Check if this is the right kind of ELF file */
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if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN) {
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fprintf(stderr, "%s: not a dynamic executable\n", filename);
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if (ehdr->e_type == ET_EXEC) {
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if (statbuf.st_mode & S_ISUID)
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if ((statbuf.st_mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP))
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fprintf(stderr, "%s: is setuid\n", filename);
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dynsec = elf_find_section_type(SHT_DYNAMIC, ehdr);
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dynamic = (Elf32_Dyn*)(dynsec->sh_offset + (int)ehdr);
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dynstr = (char *)elf_find_dynamic(DT_STRTAB, dynamic, ehdr, 0);
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find_needed_libraries(ehdr, dynamic, dynstr, is_suid);
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find_elf_interpreter(ehdr, dynamic, dynstr, is_suid);
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int main( int argc, char** argv)
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char *filename = argv[1];
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fprintf(stderr, "No filename specified.\n");
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find_dependancies(filename);
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/* Keep walking the list till everybody is resolved */
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for (cur = lib_list; cur; cur=cur->next) {
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if (cur->resolved == 0 && cur->path) {
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//printf("checking sub-depends for '%s\n", cur->path);
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find_dependancies(cur->path);
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for (cur = lib_list; cur; cur=cur->next) {
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printf("\t%s => %s\n", cur->name, cur->path);
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printf("\tnot a dynamic executable\n");
added
removed
ldso/util/ldd.c
