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/*
* Copyright © 2019-2023 Collabora Ltd.
* SPDX-License-Identifier: MIT
*
* Use libelf to parse ELF headers for DT_NEEDED, and fake the output
* format of ldd closely enough that GObject-Introspection can parse it.
*
* Limitations when compared with real ldd:
* - Only direct dependencies are output: unlike ldd, this is not recursive.
* For GObject-Introspection this is what we ideally want anyway.
* - Only bare SONAMEs are output, no paths or other extraneous information.
*/
#include <fcntl.h>
#include <stddef.h>
#include <stdio.h>
#include <unistd.h>
#include <elf.h>
#include <gelf.h>
#if 0
#define trace(...) fprintf(stderr, __VA_ARGS__)
#else
#define trace(...) do {} while (0)
#endif
int
main (int argc,
char **argv)
{
const char *library;
Elf *elf = NULL;
Elf_Scn *scn = NULL;
GElf_Shdr shdr_mem;
GElf_Shdr *shdr = NULL;
size_t phnum;
size_t i;
Elf_Data *data;
uintptr_t needed_offset = (uintptr_t) -1;
const char *needed;
size_t sh_entsize;
int fd;
if (argc != 2)
{
fprintf (stderr, "Usage: %s LIBRARY\n", argv[0]);
return 2;
}
library = argv[1];
if (elf_version (EV_CURRENT) == EV_NONE)
{
perror ("elf_version(EV_CURRENT)");
return 1;
}
if ((fd = open (library, O_RDONLY | O_CLOEXEC, 0)) < 0)
{
perror (library);
return 1;
}
if ((elf = elf_begin (fd, ELF_C_READ, NULL)) == NULL)
{
fprintf (stderr, "Error reading library %s: %s",
library, elf_errmsg (elf_errno ()));
return 1;
}
if (elf_getphdrnum (elf, &phnum) < 0)
{
fprintf (stderr, "Unable to determine the number of program headers: %s\n",
elf_errmsg (elf_errno ()));
return 1;
}
trace ("phnum=%zu\n", phnum);
for (i = 0; i < phnum; i++)
{
GElf_Phdr phdr_mem;
GElf_Phdr *phdr = gelf_getphdr (elf, i, &phdr_mem);
if (phdr != NULL && phdr->p_type == PT_DYNAMIC)
{
scn = gelf_offscn (elf, phdr->p_offset);
trace ("scn=%p\n", scn);
if (scn == NULL)
{
fprintf (stderr, "Unable to get the section: %s\n",
elf_errmsg (elf_errno ()));
return 1;
}
shdr = gelf_getshdr (scn, &shdr_mem);
trace ("shdr=%p, shdr_mem=%p\n", shdr, &shdr_mem);
if (shdr == NULL)
{
fprintf (stderr, "Unable to get the section header: %s\n",
elf_errmsg (elf_errno ()));
return 1;
}
break;
}
}
if (shdr == NULL)
{
fprintf (stderr, "Unable to find the section header\n");
return 1;
}
data = elf_getdata (scn, NULL);
if (data == NULL)
{
fprintf (stderr, "Unable to get the dynamic section data: %s\n",
elf_errmsg (elf_errno ()));
return 1;
}
trace ("data=%p\n", data);
sh_entsize = gelf_fsize (elf, ELF_T_DYN, 1, EV_CURRENT);
trace ("sh_entsize=%zu\n", sh_entsize);
for (i = 0; i < shdr->sh_size / sh_entsize; i++)
{
GElf_Dyn dyn_mem;
GElf_Dyn *dyn = gelf_getdyn (data, i, &dyn_mem);
if (dyn == NULL)
break;
if (dyn->d_tag == DT_NEEDED)
printf ("%s\n", elf_strptr (elf, shdr->sh_link, dyn->d_un.d_ptr));
}
elf_end (elf);
close (fd);
return 0;
}
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