Why does dynamic linker search global scope before local scope?

[Fengkai Sun <qcloud1014@gmail.com>]

Hi list,

After reading some LD_DEBUG messages, I've found that the dynamic linker
searches the global scope before the local scope, and the flag
RTLD_DEEPBIND can change this behavior.

I'm really curious about the reason why the dynamic linker won't search the
local scope first by default. To me, the static linker finds out the
dependencies of a DSO, and there is a very high probability that they are
defined in one of the DT_NEEDED entries. One can use the symbols in the
global scope to do interposition, but that is quite rare, so always
searching in the global scope seems tedious.

Currently, LD_PRELOAD is in the global scope, after the main executable.
Though the use of RTLD_DEEPBIND may invalidate the preload semantics, it's
just a design choice. The dynamic linker can search local scope first, and
add LD_PRELOAD somewhere in the local scope.

So I'm wondering why the dynamic linker is designed like this in the first
place.

Thanks for your time.


Best
Fengkai