In fact it all works quite nicely, I've got a test program with a little plugin module that refers back to the main program. When the main program is linked with -optl-export-dynamic the plugin can be loaded up and all symbols resolve correctly. I still had to load copies of the base packages since the plugin .o still refers to symbols not in the main executalbe. (More on that in a moment)
And yes indeed, it works with a vanilla ghc-5.04
Great stuff! I've just linked a copy of GHCi that doesn't need to load up the base package when it starts :-) However, the binary is ~15Mb compared to ~8Mb normally.
To like the whole of the base package into the binary, you can either use --whole-archive with libHSbase.a as suggested by Alastair, or link in HSbase.o. Similarly for the haskell98 package.
I got lots of linking errors about duplicate symbols doing using --whole-archive for the standard packages. Perhaps someone who knows a bit more about linking could advise me.
I couldn't get it to work either - although I didn't get any duplicate symbols when linking, it seems the resulting binary didn't have all the symbol information from the library in it. It looks like -export-dynamic doesn't work properly with --whole-archive.
ghc -optl-export-dynamic -ldl -L/usr/lib/ghc-5.04/ -lHSrts -lHSlang \ TestDLink.o -o TestDLink
since doing
ghc -optl-export-dynamic -ldl -package rst -package lang \ TestDLink.o -o TestDLink
gives: /usr/lib/ghc-5.04/libHSrts.a(RtsAPIDeprec.o): In function `rts_mkAddr': RtsAPIDeprec.o(.text+0x14): undefined reference to `Addr_Azh_con_info' /usr/lib/ghc-5.04/libHSrts.a(RtsAPIDeprec.o): In function `rts_getAddr': RtsAPIDeprec.o(.text+0x2d): undefined reference to `Addr_Azh_con_info' RtsAPIDeprec.o(.text+0x35): undefined reference to `Addr_Azh_static_info' collect2: ld returned 1 exit status
I'm not sure exactly what's going here. RtsAPIDeprec.o does refer to Addr_Azh_con_info, which is defined in the Addr module in the lang package. However, RtsAPIDeprec normally isn't linked in, because nothing refers to anything in it.
So generally quite sucessful. I should probably come up with some tutorial / documentation on doing plugins with ghc.
That's a good plan. We can probably make it easier too, perhaps by providing a flag to do the right magic at link-time. I need to think about this some more. Cheers, Simon