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

[Rui Ueyama]

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> 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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