Please take some time to read the following as I have been reading some
Wikipedia articles about libraries and have a few questions. You don't
have to answer the entire mail at once but please don't ignore it
because it's a bit long. You are my teachers here since I am neither
neither a professional programmer nor do I have a computer science
degree so I am trusting in you...
Glynn Clements wrote:
But for a shared library, the end result will be a library which
cannot actually be shared: effectively just a DLL (dynamically-linked
library) rather than a *shared* library.
I thought dll : Windows :: so : *nix. Apparently it is not so. After
reading your mail I read through the
http://en.wikipedia.org/wiki/Library_(computing) article and learnt some
things but I'm still not fully clear:
1)
A Windows DLL is a dynamic link library. I hope I am right in
understanding that to "link" means to basically resolve external
references in an object module.
http://en.wikipedia.org/wiki/Position_independent_code#Windows_DLLs
tells me that Windows DLLs would largely be shareable only on disk and
not on memory were it not for the fact that they are premapped to
certain addresses in memory.
But Unix SO files are truly shareable on memory since they use PIC.
Is that all the functional difference between Windows DLL-s and Unix SO-s?
2)
Is there a difference between a dynamic link library and a dynamic load
library? Would I be right in understanding that a dynamic link lib needs
to be loaded at the same time as (or previous to) the loading of the
caller, but a dynamic load lib can be loaded *after* the loading of the
caller? This might mean that the latter would be valid for functions. Is
my understanding correct?
3)
Is there a conflict between
http://en.wikipedia.org/wiki/Library_(computing)#Dynamic_linking and
http://en.wikipedia.org/wiki/Linker#Dynamic_linking . They have
different explanations of dynamic linking...
4)
Anyway, the first article has the phrase "index names or numbers" but it
does not say names or numbers of what. (If you tell me I will edit the
article myself.)
5)
The article http://en.wikipedia.org/wiki/Static_Library further confuses
me. It says that a static lib is a lib *in which* references to external
variables/functions are resolved at compile time. I thought it was a lib
which *satisfies* the references present *in a caller* and where the
linking is done at compile time. Should the wording be corrected?
6)
The article also says "... or at runtime by the linker or linking
loader". I think the word "respectively" should be added after "loader",
but still I don't understand how refs to symbols provided by a static
lib can be resolved at runtime. To me it goes against the very nature of
a static lib. What am I missing?
Also, on SELinux systems, you typically need to modify the security
policy to allow such libraries to be used,
Such libraries meaning?
Thanks, as always.
Shriramana.
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