How does GDB know the architecture of an executable?

[Joel Brobecker]

> I'm wondering how does GDB know the architecture of an executable, for
> example, if I use -m32 options in gcc and I can get an i386
> executable, if I use nothing I'll get a x86-64 executable while I am
> compiling code on a 64-bit Linux.
> 
> I've see the source code for one day but I cannot get what I want, at
> first I think '''struct gdbarch''' has something with it. Can anyone
> help me? I want to know everything about this.

There are a number of elements GDB uses to determine the exact
"arch" to use. A lot of it relies on the "bfd" library, which
is part of binutils, to tell us. On GNU/Linux, I'd take a look
at the ELF documentation.

-- 
Joel