dlgetfileinfo(3C)

NAME

dlgetfileinfo() — return file information for a library prior to loading it

SYNOPSIS

cc [flag... ] file... -ldl [library]...

#include <dlfcn.h>

uint64_t dlgetfileinfo(const char *file,
                       size_t info_size,
                       struct dlfileinfo *info);

Multithread Usage

This routine is thread-safe.

DESCRIPTION

dlgetfileinfo() is one of a family of routines that give the user direct access to the dynamic linking facilities (using the -ldl option on the compiler or ld command line). dlgetfileinfo() returns file information for a library prior to loading it. This information can be used to allocate load segments before calling dlopene().

file is used to construct a path name to the library. The dynamic loader searches for the library using the standard search rules used by dlopen() and dlopene(). If the library is found and is a valid shared library, dlgetfileinfo returns information about the library through the info parameter.

info_size is the size in bytes of the info buffer.

info is a pointer to a buffer allocated by the user program. The dynamic loader fills this buffer with file information.

A dlfileinfo structure has the following members:

struct dlfileinfo {
   size_t text_size;
   size_t data_size;
   char *filename;
}

text_size is the size in bytes of a shared library's text segment.

data_size is the size in bytes of a shared library's data segment.

filename is the path to the shared library. This path may be passed to a subsequent dlopen() or dlopene() call to avoid searching for the library a second time. The caller of dlgetfileinfo() must copy the value of filename to insure that it is not corrupted.

EXAMPLES

The following example illustrates the use of dlgetfileinfo() to allocate memory for mapping a shared library's data segment. For simplicity, error checking has been omitted.

      #include <dlfcn.h>
      #include <string.h>

      /* allocate_data is a user-supplied routine that allocates a
       * a memory buffer of at least "data_size" bytes and returns
       * a pointer to the buffer.
       */
      extern char *allocate_data(size_t data_size);

      int main() {
          void   *handle;
          int    status;
          char   *pathname;
          struct dlfileinfo  info;
          struct dlopen_opts opts;

          /* Locate library and get file information */
          status = dlgetfileinfo("mylib.so", sizeof(info), &info);

          if (status == 0) {

              /* Make a copy of the library pathname returned by
               * dlgetfileinfo().
               */
              pathname = strdup(info.filename);

              /* Allocate data segment */
              opts.data_addr = allocate_data(info.data_size);

              /* Not preallocating text segment */
              opts.text_addr = 0;

              /* Set dlopene() flags to indicate the data segment
               * has been preallocated.
               */
              opts.flags = RTLD_EXT_DATA_ADDR;

              /* Call dlopene() to load the library using the path
               * where dlgetfileinfo found the library and the
               * preallocated memory buffer for mapping the library's
               * data segment.
               */
              handle = dlopene(pathname, RTLD_LAZY, &opts);

              /* Remove copy of library pathname */
              free(pathname);

              /* Insert code here to use library */

              /* Close library */
              status = dlclose(handle);

              /* Insert code here to free storage allocated by
               * allocate_data().
               */
          }
      }

RETURN VALUE

If successful, dlgetfileinfo() returns 0, otherwise a non-0 value is returned. More detailed diagnostic information is available through dlerror() or dlerrno().

ERRORS

If dlgetfileinfo() fails, a subsequent call to dlerrno() returns one of the following values:

RTLD_ERR_BAD_ELF_VER: Unknown ELF version in library.
RTLD_ERR_LIB_OPEN: Unable to find library.
RTLD_ERR_NO_MEMORY: Cannot allocate dynamic memory.
RTLD_ERR_INTERNAL_ERROR: Internal error encountered in dlgetfileinfo().
RTLD_ERR_CANT_APPLY_RELOC: Failed to apply relocation while resolving call to dlgetfileinfo().
RTLD_ERR_SIGINHIBIT_FAILED: siginhibit call failed on entry to dlgetfileinfo().
RTLD_ERR_SIGENABLE_FAILED: sigenable call failed on exit from dlgetfileinfo().
RTLD_ERR_BAD_ABI1: ABI mismatch because a 64-bit program found a 32-bit shared library.
RTLD_ERR_BAD_ABI2: ABI mismatch because a 32-bit program found a 64-bit shared library.
RTLD_ERR_BAD_DLL_MAGIC_NUM: The library is invalid due to a bad magic number.
RTLD_ERR_BAD_DLL_BAD_MACHINE: The library is invalid due to a bad machine type.
RTLD_ERR_BAD_DLL_BAD_OBJFILE: The library is invalid due to a bad object file type.
RTLD_ERR_SETCANCELSTATE_FAILED: __thread_setcancelstate failed on entry to or exit from dlgetfileinfo().
RTLD_ERR_DLGETFILEINFO_MTEXT: Cannot return file information because the library has multiple text segments.
RTLD_ERR_DLGETFILEINFO_MDATA: Cannot return file information because the library has multiple data segments.
RTLD_ERR_INV_DLGETFILEINFO_ARGUMENT: Invalid argument in call to dlgetfileinfo().
RTLD_ERR_DLGETFILEINFO_IO: An IO error occurred while reading the file information.

dlgetfileinfo(3C)

Technical documentation

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