It's incorrect to speak of "the" text segment, since there may be more than one (guaranteed for the usual case when you have shared libraries, but it's still possible for a single ELF binary to have multiple PT_LOAD sections with the same flags anyway).
The following sample program dumps out all the information returned by dl_iterate_phr. You're interested in any segment of type PT_LOAD with the PF_X flag (note that PT_GNU_STACK will include the flag if -z execstack is passed to the linker, so you really do have to check both).
#define _GNU_SOURCE
#include <link.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
const char *type_str(ElfW(Word) type)
{
switch (type)
{
case PT_NULL:
return "PT_NULL"; // should not be seen at runtime, only in the file!
case PT_LOAD:
return "PT_LOAD";
case PT_DYNAMIC:
return "PT_DYNAMIC";
case PT_INTERP:
return "PT_INTERP";
case PT_NOTE:
return "PT_NOTE";
case PT_SHLIB:
return "PT_SHLIB";
case PT_PHDR:
return "PT_PHDR";
case PT_TLS:
return "PT_TLS";
case PT_GNU_EH_FRAME:
return "PT_GNU_EH_FRAME";
case PT_GNU_STACK:
return "PT_GNU_STACK";
case PT_GNU_RELRO:
return "PT_GNU_RELRO";
case PT_SUNWBSS:
return "PT_SUNWBSS";
case PT_SUNWSTACK:
return "PT_SUNWSTACK";
default:
if (PT_LOOS <= type && type <= PT_HIOS)
{
return "Unknown OS-specific";
}
if (PT_LOPROC <= type && type <= PT_HIPROC)
{
return "Unknown processor-specific";
}
return "Unknown";
}
}
const char *flags_str(ElfW(Word) flags)
{
switch (flags & (PF_R | PF_W | PF_X))
{
case 0 | 0 | 0:
return "none";
case 0 | 0 | PF_X:
return "x";
case 0 | PF_W | 0:
return "w";
case 0 | PF_W | PF_X:
return "wx";
case PF_R | 0 | 0:
return "r";
case PF_R | 0 | PF_X:
return "rx";
case PF_R | PF_W | 0:
return "rw";
case PF_R | PF_W | PF_X:
return "rwx";
}
__builtin_unreachable();
}
static int callback(struct dl_phdr_info *info, size_t size, void *data)
{
int j;
(void)data;
printf("object \"%s\"\n", info->dlpi_name);
printf(" base address: %p\n", (void *)info->dlpi_addr);
if (size > offsetof(struct dl_phdr_info, dlpi_adds))
{
printf(" adds: %lld\n", info->dlpi_adds);
}
if (size > offsetof(struct dl_phdr_info, dlpi_subs))
{
printf(" subs: %lld\n", info->dlpi_subs);
}
if (size > offsetof(struct dl_phdr_info, dlpi_tls_modid))
{
printf(" tls modid: %zu\n", info->dlpi_tls_modid);
}
if (size > offsetof(struct dl_phdr_info, dlpi_tls_data))
{
printf(" tls data: %p\n", info->dlpi_tls_data);
}
printf(" segments: %d\n", info->dlpi_phnum);
for (j = 0; j < info->dlpi_phnum; j++)
{
const ElfW(Phdr) *hdr = &info->dlpi_phdr[j];
printf(" segment %2d\n", j);
printf(" type: 0x%08X (%s)\n", hdr->p_type, type_str(hdr->p_type));
printf(" file offset: 0x%08zX\n", hdr->p_offset);
printf(" virtual addr: %p\n", (void *)hdr->p_vaddr);
printf(" physical addr: %p\n", (void *)hdr->p_paddr);
printf(" file size: 0x%08zX\n", hdr->p_filesz);
printf(" memory size: 0x%08zX\n", hdr->p_memsz);
printf(" flags: 0x%08X (%s)\n", hdr->p_flags, flags_str(hdr->p_flags));
printf(" align: %zd\n", hdr->p_align);
if (hdr->p_memsz)
{
printf(" derived address range: %p to %p\n",
(void *) (info->dlpi_addr + hdr->p_vaddr),
(void *) (info->dlpi_addr + hdr->p_vaddr + hdr->p_memsz));
}
}
return 0;
}
int main(void)
{
dl_iterate_phdr(callback, NULL);
exit(EXIT_SUCCESS);
}
