Linker – S3lab

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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Hardening binaries (VI) – RELRO

Sat, 04 Feb 2017 15:11:25 +0000

In this post we are going to talk about two options that can happen to the linker to make certain sections of our executable more secure: -Wl, -z, relro, -z, now. When a program calls a function not defined in the program, which is in a shared library, the GOT (Global Shift Table) and PLT (Procedure Linking Table) sections come into play, which are responsible for specifying where that Function we need (see this link for a more detailed explanation). For example, if we use printing in a program and look at what is happening in assembly:

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