[mercury-users] Order of --link-object args

[Zoltan Somogyi]

On 20-Aug-2010, Ondrej Bojar <bojar at ufal.mff.cuni.cz> wrote:
> I'm linking against a library originally implemented in C and against a 
> Mercury wrapper library (not "installed"). If I run:
>
> mmc --make \
>   ...
>   --link-object lib-the-c-one.a \
>   --link-object lib-the-wrapper.a \
>   target
>
> I get lot of undefined references to symbols actually present in 
> lib-the-c-one.a (I double checked with nm).
>
> If I reorder the two --link-object arguments, it links correctly:
>
> mmc --make \
>   ...
>   --link-object lib-the-wrapper.a \
>   --link-object lib-the-c-one.a \
>   target

Basically, the order in which you supply things to be linked is the order
in which mmc gives those things to the linker. If the linker has not seen
any reference to any of the symbols defined by lib-the-c-one.a when it
processes lib-the-c-one.a, then it won't pull any object files from
lib-the-c-one.a into the executable. By the time it sees such references
in lib-the-wrapper.a, it is too late; the linker never goes back to process
a previously processed library again.

This behavior is WHY mmc allows you to control the order of libraries to be
linked by naming them in the order you want them to be given to the linker.

Zoltan.
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