Differentiate b/w dynamic and static executables.

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Differentiate b/w dynamic and static executables.

Umesh Kalappa
Hi All,

We have a situation, where we defined the program segments like in the
linker script

PHDRS
{
  headers PT_PHDR PHDRS ;
  interp PT_INTERP ;
  text PT_LOAD FILEHDR PHDRS ;
  data PT_LOAD ;
  tls PT_TLS ;
  dynamic PT_DYNAMIC ;
  note PT_NOTE ;
  stack PT_GNU_STACK FLAGS(6);
}

for the static executable, where we don't need PT_DYNAMIC segment, but
still  the final executable has the program segments like

Elf file type is EXEC (Executable file)
Entry point 0x2000037f1
There are 8 program headers, starting at offset 64

Program Headers:
  Type           Offset   VirtAddr           PhysAddr           FileSiz
 MemSiz   Flg Align
  PHDR           0x000040 0x0000000200000040 0x0000000200000040 0x0001c0
0x0001c0 R   0x8
  INTERP         0x000200 0x0000000200000200 0x0000000200000200 0x00000f
0x00000f R   0x1
      [Requesting program interpreter: /lib/ld64.so.1]
  LOAD           0x000000 0x0000000200000000 0x0000000200000000 0x011100
0x011100 R E 0x1000
  LOAD           0x011fd0 0x0000000200013fd0 0x0000000200013fd0 0x000330
0x000898 RW  0x1000
  TLS            0x000000 0x0000000000000000 0x0000000000000000 0x000000
0x000000     0x8
  DYNAMIC        0x000000 0x0000000000000000 0x0000000000000000 0x000000
0x000000     0x8
readelf: Warning: the .dynamic section is not contained within the dynamic
segment
  NOTE           0x000000 0x0000000000000000 0x0000000000000000 0x000000
0x000000     0x8
  GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000
0x000000 RW  0x8

Version used :

GNU ld (GNU Binutils) 2.33.1
Copyright (C) 2019 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) a later
version.
This program has absolutely no warranty.

$file final.exe
ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked,
interpreter *empty*, not stripped

the same script used both static and dynamic executables, one solution
would be like have two scripts with PT_DYNAMIC and without.

But any inputs or suggestions, how we can use the unified script for both
static and dynamic executables?

Thank you
~Umesh
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Re: Differentiate b/w dynamic and static executables.

Simon Richter-2
Hi,

On 26.12.19 14:46, Umesh Kalappa wrote:

> for the static executable, where we don't need PT_DYNAMIC segment, but
> still  the final executable has the program segments like

The static executable also doesn't need a PT_INTERP segment, in fact it
shouldn't have one.

It might in theory be possible to build a unified linker script, but I'd
expect separate scripts to be more maintainable. If you do something
interesting in a script like collect fragments into lists (like C++
global initializers) then it is usually better to make a preliminary
link with a linker script that resolves the common parts and generates
another relocatable output, and then a final link that maps the sections
to segments.

Note that the standard C and C++ libraries are very much dependent on
their startup code, and that startup code defines a set of sections that
need to be linked in a particular way to work, so at the very least your
scripts also need to know about the requirements of the C/C++ libraries
you use.

The linker scripts shipped with the compiler are generated with a
preprocessor from a common source, but separate scripts are generated
for different cases (static/dynamic/shared/... debug/nodebug ...), so it
is likely not possible in a sensible way.

   Simon


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