Re: [Qemu-devel] [RFC 48/48] plugin: add a couple of very simple examples

[Emilio G. Cota]

On Thu, Nov 29, 2018 at 23:45:18 +0300, Roman Bolshakov wrote:
> On Thu, Oct 25, 2018 at 01:20:57PM -0400, Emilio G. Cota wrote:
> > +
> > +lib%.so: %.o
> > +   $(CC) -shared -Wl,-soname,$@ -o $@ $^ $(LDLIBS)
> 
> The rule should be a bit different for macOS:
> %.bundle: %.o
>        $(CC) -bundle -Wl,-bundle_loader,PATH_TO_QEMU_EXE -o $@ $^ $(LDLIBS)
> 
> "-bundle" flag is needed because macOS has two kinds of Mach-O
> dynamically loaded executables:
>  - dylib (MH_DYLIB) - it's like an ELF shared object used for dynamic
>    linking. Can be loaded, preloaded for sake of function interposing
>    but cannot be explicitly unloaded.
>  - bundle (MH_BUNDLE) - similar to an ELF shared object used in plugin
>    dlopen/dlclose scenario.
> 
> We can pick any (enabled in configure) qemu-system executable as
> bundle_loader. We specify it to check if all symbols in a bundle,
> including the ones coming from the executable are defined. FWIW, here's
> the reference for bundle_loader flag:
>   -bundle_loader executable
>       This specifies the executable that will be loading the bundle
>       output file being linked. Undefined symbols from the bundle are
>       checked against the specified executable like it was one of the
>       dynamic libraries the bundle was linked with
> 
> 
> The ".bundle" extension is not required but IMO it feels more native to
> the system than ".so".

The goal of the examples is to be target-independent, so I'm not
convinced that we want to bury $PATH_TO_QEMU_EXE in the build recipe
(or get configure involved in this).

Since you say the "bundle" business isn't a requirement, I'll leave just
the .so rule in v2.

Thanks,

                Emilio