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tclLoadAix.c

/*
 * tclLoadAix.c --
 *
 *    This file implements the dlopen and dlsym APIs under the AIX operating
 *    system, to enable the Tcl "load" command to work. This code was
 *    provided by Jens-Uwe Mager.
 *
 *    This file is subject to the following copyright notice, which is
 *    different from the notice used elsewhere in Tcl. The file has been
 *    modified to incorporate the file dlfcn.h in-line.
 *
 *    Copyright (c) 1992,1993,1995,1996, Jens-Uwe Mager, Helios Software GmbH
 *    Not derived from licensed software.
 *
 *    Permission is granted to freely use, copy, modify, and redistribute
 *    this software, provided that the author is not construed to be liable
 *    for any results of using the software, alterations are clearly marked
 *    as such, and this notice is not modified.
 *
 * RCS: @(#) $Id: tclLoadAix.c,v 1.6 2007/04/16 13:36:36 dkf Exp $
 *
 * Note: this file has been altered from the original in a few ways in order
 * to work properly with Tcl.
 */

/*
 * @(#)dlfcn.c    1.7 revision of 95/08/14  19:08:38
 * This is an unpublished work copyright (c) 1992 HELIOS Software GmbH
 * 30159 Hannover, Germany
 */

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ldr.h>
#include <a.out.h>
#include <ldfcn.h>
#include "../compat/dlfcn.h"

/*
 * We simulate dlopen() et al. through a call to load. Because AIX has no call
 * to find an exported symbol we read the loader section of the loaded module
 * and build a list of exported symbols and their virtual address.
 */

typedef struct {
    char *name;               /* The symbols's name. */
    void *addr;               /* Its relocated virtual address. */
} Export, *ExportPtr;

/*
 * xlC uses the following structure to list its constructors and destructors.
 * This is gleaned from the output of munch.
 */

typedef struct {
    void (*init)(void);       /* call static constructors */
    void (*term)(void);       /* call static destructors */
} Cdtor, *CdtorPtr;

/*
 * The void * handle returned from dlopen is actually a ModulePtr.
 */

typedef struct Module {
    struct Module *next;
    char *name;               /* module name for refcounting */
    int refCnt;               /* the number of references */
    void *entry;        /* entry point from load */
    struct dl_info *info;     /* optional init/terminate functions */
    CdtorPtr cdtors;          /* optional C++ constructors */
    int nExports;       /* the number of exports found */
    ExportPtr exports;        /* the array of exports */
} Module, *ModulePtr;

/*
 * We keep a list of all loaded modules to be able to call the fini handlers
 * and destructors at atexit() time.
 */

static ModulePtr modList;

/*
 * The last error from one of the dl* routines is kept in static variables
 * here. Each error is returned only once to the caller.
 */

static char errbuf[BUFSIZ];
static int errvalid;

static void caterr(char *);
static int readExports(ModulePtr);
static void terminate(void);
static void *findMain(void);

void *
dlopen(
    const char *path,
    int mode)
{
    register ModulePtr mp;
    static void *mainModule;

    /*
     * Upon the first call register a terminate handler that will close all
     * libraries. Also get a reference to the main module for use with
     * loadbind.
     */

    if (!mainModule) {
      mainModule = findMain();
      if (mainModule == NULL) {
          return NULL;
      }
      atexit(terminate);
    }

    /*
     * Scan the list of modules if we have the module already loaded.
     */

    for (mp = modList; mp; mp = mp->next) {
      if (strcmp(mp->name, path) == 0) {
          mp->refCnt++;
          return (void *) mp;
      }
    }

    mp = (ModulePtr) calloc(1, sizeof(*mp));
    if (mp == NULL) {
      errvalid++;
      strcpy(errbuf, "calloc: ");
      strcat(errbuf, strerror(errno));
      return NULL;
    }

    mp->name = malloc((unsigned) (strlen(path) + 1));
    strcpy(mp->name, path);

    /*
     * load should be declared load(const char *...). Thus we cast the path to
     * a normal char *. Ugly.
     */

    mp->entry = (void *) load((char *)path, L_NOAUTODEFER, NULL);
    if (mp->entry == NULL) {
      free(mp->name);
      free(mp);
      errvalid++;
      strcpy(errbuf, "dlopen: ");
      strcat(errbuf, path);
      strcat(errbuf, ": ");

      /*
       * If AIX says the file is not executable, the error can be further
       * described by querying the loader about the last error.
       */

      if (errno == ENOEXEC) {
          char *tmp[BUFSIZ/sizeof(char *)], **p;

          if (loadquery(L_GETMESSAGES, tmp, sizeof(tmp)) == -1) {
            strcpy(errbuf, strerror(errno));
          } else {
            for (p=tmp ; *p ; p++) {
                caterr(*p);
            }
          }
      } else {
          strcat(errbuf, strerror(errno));
      }
      return NULL;
    }

    mp->refCnt = 1;
    mp->next = modList;
    modList = mp;

    if (loadbind(0, mainModule, mp->entry) == -1) {
    loadbindFailure:
      dlclose(mp);
      errvalid++;
      strcpy(errbuf, "loadbind: ");
      strcat(errbuf, strerror(errno));
      return NULL;
    }

    /*
     * If the user wants global binding, loadbind against all other loaded
     * modules.
     */

    if (mode & RTLD_GLOBAL) {
      register ModulePtr mp1;

      for (mp1 = mp->next; mp1; mp1 = mp1->next) {
          if (loadbind(0, mp1->entry, mp->entry) == -1) {
            goto loadbindFailure;
          }
      }
    }

    if (readExports(mp) == -1) {
      dlclose(mp);
      return NULL;
    }

    /*
     * If there is a dl_info structure, call the init function.
     */

    if (mp->info = (struct dl_info *)dlsym(mp, "dl_info")) {
      if (mp->info->init) {
          (*mp->info->init)();
      }
    } else {
      errvalid = 0;
    }

    /*
     * If the shared object was compiled using xlC we will need to call static
     * constructors (and later on dlclose destructors).
     */

    if (mp->cdtors = (CdtorPtr) dlsym(mp, "__cdtors")) {
      while (mp->cdtors->init) {
          (*mp->cdtors->init)();
          mp->cdtors++;
      }
    } else {
      errvalid = 0;
    }

    return (void *) mp;
}

/*
 * Attempt to decipher an AIX loader error message and append it to our static
 * error message buffer.
 */

static void
caterr(
    char *s)
{
    register char *p = s;

    while (*p >= '0' && *p <= '9') {
      p++;
    }
    switch (atoi(s)) {        /* INTL: "C", UTF safe. */
    case L_ERROR_TOOMANY:
      strcat(errbuf, "to many errors");
      break;
    case L_ERROR_NOLIB:
      strcat(errbuf, "can't load library");
      strcat(errbuf, p);
      break;
    case L_ERROR_UNDEF:
      strcat(errbuf, "can't find symbol");
      strcat(errbuf, p);
      break;
    case L_ERROR_RLDBAD:
      strcat(errbuf, "bad RLD");
      strcat(errbuf, p);
      break;
    case L_ERROR_FORMAT:
      strcat(errbuf, "bad exec format in");
      strcat(errbuf, p);
      break;
    case L_ERROR_ERRNO:
      strcat(errbuf, strerror(atoi(++p)));      /* INTL: "C", UTF safe. */
      break;
    default:
      strcat(errbuf, s);
      break;
    }
}

void *
dlsym(
    void *handle,
    const char *symbol)
{
    register ModulePtr mp = (ModulePtr)handle;
    register ExportPtr ep;
    register int i;

    /*
     * Could speed up the search, but I assume that one assigns the result to
     * function pointers anyways.
     */

    for (ep = mp->exports, i = mp->nExports; i; i--, ep++) {
      if (strcmp(ep->name, symbol) == 0) {
          return ep->addr;
      }
    }

    errvalid++;
    strcpy(errbuf, "dlsym: undefined symbol ");
    strcat(errbuf, symbol);
    return NULL;
}

char *
dlerror(void)
{
    if (errvalid) {
      errvalid = 0;
      return errbuf;
    }
    return NULL;
}

int
dlclose(
    void *handle)
{
    register ModulePtr mp = (ModulePtr)handle;
    int result;
    register ModulePtr mp1;

    if (--mp->refCnt > 0) {
      return 0;
    }

    if (mp->info && mp->info->fini) {
      (*mp->info->fini)();
    }

    if (mp->cdtors) {
      while (mp->cdtors->term) {
          (*mp->cdtors->term)();
          mp->cdtors++;
      }
    }

    result = unload(mp->entry);
    if (result == -1) {
      errvalid++;
      strcpy(errbuf, strerror(errno));
    }

    if (mp->exports) {
      register ExportPtr ep;
      register int i;
      for (ep = mp->exports, i = mp->nExports; i; i--, ep++) {
          if (ep->name) {
            free(ep->name);
          }
      }
      free(mp->exports);
    }

    if (mp == modList) {
      modList = mp->next;
    } else {
      for (mp1 = modList; mp1; mp1 = mp1->next) {
          if (mp1->next == mp) {
            mp1->next = mp->next;
            break;
          }
      }
    }

    free(mp->name);
    free(mp);
    return result;
}

static void
terminate(void)
{
    while (modList) {
      dlclose(modList);
    }
}

/*
 * Build the export table from the XCOFF .loader section.
 */

static int
readExports(
    ModulePtr mp)
{
    LDFILE *ldp = NULL;
    SCNHDR sh, shdata;
    LDHDR *lhp;
    char *ldbuf;
    LDSYM *ls;
    int i;
    ExportPtr ep;
    const char *errMsg;

#define Error(msg) do{errMsg=(msg);goto error;}while(0)
#define SysErr() Error(strerror(errno))

    ldp = ldopen(mp->name, ldp);
    if (ldp == NULL) {
      struct ld_info *lp;
      char *buf;
      int size = 0;

      if (errno != ENOENT) {
          SysErr();
      }

      /*
       * The module might be loaded due to the LIBPATH environment variable.
       * Search for the loaded module using L_GETINFO.
       */

      while (1) {
          size += 4 * 1024;
          buf = malloc(size);
          if (buf == NULL) {
            SysErr();
          }

          i = loadquery(L_GETINFO, buf, size);

          if (i != -1) {
            break;
          }
          free(buf);
          if (errno != ENOMEM) {
            SysErr();
          }
      }

      /*
       * Traverse the list of loaded modules. The entry point returned by
       * load() does actually point to the data segment origin.
       */

      lp = (struct ld_info *) buf;
      while (lp) {
          if (lp->ldinfo_dataorg == mp->entry) {
            ldp = ldopen(lp->ldinfo_filename, ldp);
            break;
          }
          if (lp->ldinfo_next == 0) {
            lp = NULL;
          } else {
            lp = (struct ld_info *)((char *)lp + lp->ldinfo_next);
          }
      }

      free(buf);

      if (!ldp) {
          SysErr();
      }
    }

    if (TYPE(ldp) != U802TOCMAGIC) {
      Error("bad magic");
    }

    /*
     * Get the padding for the data section. This is needed for AIX 4.1
     * compilers. This is used when building the final function pointer to the
     * exported symbol.
     */

    if (ldnshread(ldp, _DATA, &shdata) != SUCCESS) {
      Error("cannot read data section header");
    }

    if (ldnshread(ldp, _LOADER, &sh) != SUCCESS) {
      Error("cannot read loader section header");
    }

    /*
     * We read the complete loader section in one chunk, this makes finding
     * long symbol names residing in the string table easier.
     */

    ldbuf = (char *) malloc(sh.s_size);
    if (ldbuf == NULL) {
      SysErr();
    }

    if (FSEEK(ldp, sh.s_scnptr, BEGINNING) != OKFSEEK) {
      free(ldbuf);
      Error("cannot seek to loader section");
    }

    if (FREAD(ldbuf, sh.s_size, 1, ldp) != 1) {
      free(ldbuf);
      Error("cannot read loader section");
    }

    lhp = (LDHDR *) ldbuf;
    ls = (LDSYM *)(ldbuf + LDHDRSZ);

    /*
     * Count the number of exports to include in our export table.
     */

    for (i = lhp->l_nsyms; i; i--, ls++) {
      if (!LDR_EXPORT(*ls)) {
          continue;
      }
      mp->nExports++;
    }

    mp->exports = (ExportPtr) calloc(mp->nExports, sizeof(*mp->exports));
    if (mp->exports == NULL) {
      free(ldbuf);
      SysErr();
    }

    /*
     * Fill in the export table. All entries are relative to the entry point
     * we got from load.
     */

    ep = mp->exports;
    ls = (LDSYM *)(ldbuf + LDHDRSZ);
    for (i=lhp->l_nsyms ; i!=0 ; i--,ls++) {
      char *symname;
      char tmpsym[SYMNMLEN+1];

      if (!LDR_EXPORT(*ls)) {
          continue;
      }

      if (ls->l_zeroes == 0) {
          symname = ls->l_offset + lhp->l_stoff + ldbuf;
      } else {
          /*
           * The l_name member is not zero terminated, we must copy the
           * first SYMNMLEN chars and make sure we have a zero byte at the
           * end.
           */

          strncpy(tmpsym, ls->l_name, SYMNMLEN);
          tmpsym[SYMNMLEN] = '\0';
          symname = tmpsym;
      }
      ep->name = malloc((unsigned) (strlen(symname) + 1));
      strcpy(ep->name, symname);
      ep->addr = (void *)((unsigned long)
            mp->entry + ls->l_value - shdata.s_vaddr);
      ep++;
    }
    free(ldbuf);
    while (ldclose(ldp) == FAILURE) {
      /* Empty body */
    }
    return 0;

    /*
     * This is a factoring out of the error-handling code to make the rest of
     * the function much simpler to read.
     */

  error:
    errvalid++;
    strcpy(errbuf, "readExports: ");
    strcat(errbuf, errMsg);

    if (ldp != NULL) {
      while (ldclose(ldp) == FAILURE) {
          /* Empty body */
      }
    }
    return -1;
}

/*
 * Find the main modules entry point. This is used as export pointer for
 * loadbind() to be able to resolve references to the main part.
 */

static void *
findMain(void)
{
    struct ld_info *lp;
    char *buf;
    int size = 4*1024;
    int i;
    void *ret;

    buf = malloc(size);
    if (buf == NULL) {
      goto error;
    }

    while ((i = loadquery(L_GETINFO, buf, size)) == -1 && errno == ENOMEM) {
      free(buf);
      size += 4*1024;
      buf = malloc(size);
      if (buf == NULL) {
          goto error;
      }
    }

    if (i == -1) {
      free(buf);
      goto error;
    }

    /*
     * The first entry is the main module. The entry point returned by load()
     * does actually point to the data segment origin.
     */

    lp = (struct ld_info *) buf;
    ret = lp->ldinfo_dataorg;
    free(buf);
    return ret;

  error:
    errvalid++;
    strcpy(errbuf, "findMain: ");
    strcat(errbuf, strerror(errno));
    return NULL;
}

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */

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