Irene Díez – S3lab

Fatal optimizations

Tue, 21 Nov 2017 10:57:14 +0000

Compilers transform the code we write to make it more efficient, however, there are times when these optimizations made by the compiler can cause security problems. A clear example of this is the dead code elimination, an optimization that aims…

How does a linker work? (III) – Types of symbols

Sat, 14 Oct 2017 10:00:40 +0000

After learning what information contains the symbol table in the previous post, we can now talk more about the attributes that a symbol can have and what role do they have in the resolution of symbols from the linker point of view.. Remember that the symbols can be global (global), local (local) or weak. Globals are non-static defined functions in addition to the initialized variables defined without static. A local symbol is one defined with a static, and finally the weak symbols are the uninitialized global variables.

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How does a linker work? (II) – The symbol table

Fri, 15 Sep 2017 16:00:08 +0000

In previous posts we talked about that the linkers are the ones in charge of combining different files of translatable object code in an executable. For this they had two fundamental tasks, the resolution of symbols and the transfer; in this installment we are going to start talking about the resolution of symbols, that remember is the act of associating each reference of a symbol with its definition.

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How does a linker work? (I)

Tue, 11 Jul 2017 19:36:41 +0000

In the process of converting the code from a high level language to an executable that understands our system, the linkers have a role that often goes unnoticed, but that is important to know. When we want to convert a .c file into an executable several tools come into play: first the C preprocessor (called cpp) generates an intermediate file, where, among other things, the #define directives are expanded and the comments are deleted.

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Create an unreadable binary with these techniques

Fri, 23 Jun 2017 09:57:36 +0000

Whether for malicious purposes, such as the case of malware authors, for corporate purposes, or for other reasons, obfuscation techniques are used to protect a program by making compiled binary static analysis more costly. Obfuscation therefore consists of transforming a…

How does a compiler work?

Sat, 13 May 2017 18:28:39 +0000

In the series Hardening binaries posts you have seen that many defenses are implanted in the compilers themselves, but how are they implemented? Taking the case of GCC, the GNU compiler collection, let’s explain the general GCC infrastructure and roughly how…