The following working patchset demonstrates a one step to plugins system: it moves various dependent libraries and stuff out from libs_softmmu or libs_tools to object-specific variables. When that object is linked into final executable, corresponding libs are expanded and appended to the linking command line.
I took block/curl.o as an example (in the last patch). This is a working example which can be used as is as a starting point to convert other similar cases. There are a few questions still. I'm not sure whenever this $(obj)foo.o syntax (instead of $(obj)/foo.o) is okay, using the slash is more natural, but when you realize that objects can be stored in current dir it may be okay. However, it is easy to make mistakes here in new code -- probably trivially catchable. The foo.cflags isn't really necessary, but when you specify one thing one way (target-specific variable), and another thing completely different way, resulting code does not look nice. In particular, the two curl definitions in block/Makefile.objs look somewhat funky if curl.cflags isn't used. It is quite a bit ugly to strip out ../ in the link line, but it is also ugly to add that ../ in the first place. Maybe I should add a comment in Makefile.target where it adds ../ to also refer to rules.mak, and back, for clarity. In configure, we may define $(obj)curl.libs directly, but for that to work we should know where exactly the curl.o is located. At the same time, we may just as well use basenames (without paths) to define per-object variables -- this way we wont need to strip ./ from $(obj) or any other black magic, but we should ensure that all basenames are unique, or else bad things may happen. When you build a library from an object, its libs aren't propagated. It is fixable, by creating library.libs variables and expanding them at executable link time, but since not all objects from the lib may be necessary, this isn't nice. Generally, is is expected that obj.libs variables will be used only for common optional objects like "plugins". Michael Tokarev (4): build-sys: strip leading ./ from $(obj) build-sys: allow object-specific libraries to be used to link executables build-sys: allow per-object foo.cflags variables build-sys: move -lcurl out of libs and specify it for curl.o audio/Makefile.objs | 4 ++-- backends/Makefile.objs | 2 +- block/Makefile.objs | 4 ++-- configure | 3 +-- hw/audio/Makefile.objs | 2 +- rules.mak | 16 ++++++++++------ trace/Makefile.objs | 26 +++++++++++++------------- ui/Makefile.objs | 6 +++--- 8 files changed, 33 insertions(+), 30 deletions(-) -- 1.7.10.4
