[PATCH][lld][PECOFF] Add Support for entry point symbol name

[Jesús Serrano]

It's perfectly ok to me that you submit the patch just as it is, as you 
said, it is useful.

In the other hand, I've been thinking how to implement the final link 
behavior. The search of the entry point symbol must be done obviously 
after the input reading. I think that also after the resolve phase, 
since the " _main" symbol could be defined in a shared library. One 
possible solution would be to search inside a new Pass before the 
writing. What do you think?


On 23/08/2013 1:19, Rui Ueyama wrote:
> Thank you for the investigation. This is more complex than I thought 
> and very interesting. This behavior needs to be implemented for 
> link.exe compatibility. It doesn't make sense to implement this in the 
> driver as you wrote and should be in the linking context.
>
> I want submit your patch for now, as it's useful. You'll be able to 
> remove the code from the driver and add new code to the linking 
> context. Does this sound good?
>
> On Tue, Aug 20, 2013 at 1:07 PM, Jesús Serrano <dagonoweda at gmail.com 
> <mailto:dagonoweda at gmail.com>> wrote:
>
>
>         I've attached a new patch with this changes. Now the windows
>         driver sets the entry symbol name according to the
>         corresponding options. However, this won't work in all cases.
>         Depending onwhether the crt is compiled as multibyte or
>         unicode, the entry point symbol name changes from
>         "mainCRTStartup" to "wmainCRTStartup", and the same for the
>         windows subsystem. The problem with this is that the use of
>         unicode is unknown at link time (or at least I don't know how
>         to retrieve this option from object files). One possible
>         solution would be to have two entry point names in the linking
>         context, and find a symbol mathing any of them, but I don't
>         like it so much. Any ideas on this?
>
>
>     I've looking into this, and seems that LINK.EXE behavior for
>     executable images is to "select" the CRT entry point depending on
>     the symbols defined in the object files.
>      If neither the subsystem nor the entry point are defined in
>     command line arguments, the linker searches for the symbols
>     "_main", "_wmain", "_WinMain" and "_wWinMain". Depending on the
>     found symbols, the linker chooses the subsystem and the CRT entry
>     point, having "_main" the highest priority and "_wWinMain" the
>     lesser. This is, if "_main" is defined, the subsystem will be
>     CONSOLE and the CRT entry point "_mainCRTStartup", and so on. If
>     several of these entry point symbols for the same subsystem are
>     defined, the linker chooses the symbol of higher priority and
>     prints a warning.
>     If the subsystem is defined in the command line, then the linker
>     searches only for the corresponding entry point symbols to choose
>     between the unicode and the multibyte CRT entry point.
>     If the entry point symbol is defined in the command line, but not
>     the subsystem, the linker forces to choose one and throws an error.
>
>     If we want to follow this behavior, it has no sense to let the
>     driver to choose the entry point symbol name. This could be
>     handled by the linking context after the file parsing or the by
>     writer, what do you think about that?
>
>

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