Potential of a compiler that creates the executable at once

[sfp]

On Friday, 11 February 2022 at 06:33:20 UTC, Walter Bright wrote:
> On 2/10/2022 7:45 PM, max haughton wrote:
>> If by hook you mean a callback of sorts that can be overrided, 
>> then the problem solved is not strictly the same as a weakly 
>> defined function. If you have multiple library's in the same 
>> playpen then it simply doesn't work to have them all trying to 
>> override the same symbols. If they can neatly hook and unhook 
>> things that goes away.
>
> That's not how multiple libraries work.
>
> Suppose you have 3 libraries, A, B, and C. You have an object 
> file X. The linker command is:
>
>     link X.obj A.lib B.lib C.lib
>
> X refers to "foo". All 4 define "foo". Which one gets picked?
>
>    X.foo
>
> That's it. There are no unresolved symbols to look for.
>
> Now, suppose only B and C define "foo". Which one gets picked?
>
>    B.foo
>
> because it is not in X. Then, A is looked at, and it is not in 
> A. Then, B is looked at, and it is in B. C is not looked at 
> because it is now resolved.
>
> It has nothing to do with weak definitions. It's a simple "foo" 
> is referenced. Got to find a definition. Look in the libraries 
> in the order they are supplied to the linker.
>
> That's it.
>
> Want to not use the library definition? Define it yourself in 
> X. No need for hooking. No need for anything clever at all. 
> Just define it in your .obj file.
>
> ----
>
> Now suppose X.obj and Y.obj both define foo. Link with:
>
>     link X.obj Y.obj A.lib B.lib C.lib
>
> You get a message:
>
>     Multiple definition of "foo", found in X.obj and Y.obj
>
> because order does not matter for .obj files as far as symbols 
> go. All the symbols in .obj files get added.

You have now successfully explained this to at least one 
programmer! :-) Very good explanation, and very simple mechanism 
indeed. Had no idea it worked this way.

Inspired by this, I did a little searching and found this blog 
post:

http://www.samanbarghi.com/blog/2014/09/05/how-to-wrap-a-system-call-libc-function-in-linux/

One of these days I should get around to learning all the things 
the toolchain can actually do for me!