Re: code that went to process segment now goes to shared segment

[Alexander Monakov <amonakov@ispras.ru>]

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On Fri, 6 Dec 2019, bmuller@inf.ufpr.br wrote:

> After compiling with gcc 5.4.0 (gcc (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0
> 20160609),  the execution shows that the procedure "main" was at address
> 0x400776, that is, in the process segment (along the global variables).
> 
> After compiling with gcc 7.4.0 (gcc (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0),
> the execution  shows that the procedure "main" went to address
> 0x55bbddb7e7fa, that is inside the dynamic segment área (along the global
> variables).
> 
> I guess that this "functional" change occurred along the GCC 6.0 changes,
> but I could not find the motivation for it in the wiki, faq or the 6.0
> change docs.
> 
> My question is if there is some documentation that presents the motivation
> for this changes: advantages, disadvantages and if some abnormal behavior
> was reported.

You're seeing that newer Ubuntu configures GCC to produce position-independent
executables by default (look for --enable-default-pie in output of 'gcc -v').

Each distribution decides for itself whether to enable PIE by default or not,
the motivation is security hardening; I think you can look for articles on
ASLR, address space layout randomization, for further info.

Upstream GCC did not change its defaults with regard to PIE-by-default, this
was and remains up to distributions.

Alexander