On 12/9/22 17:52, Peter Maydell wrote:
Dependencies are usually added near the .c files that use them. That's
a bit messy of course if you have an "#include <>" in a heavily-included
QEMU header. You can consider it a way to discourage heavily-included
headers.
This has always seemed to me to be a recipe for bugs that only
show up in the uncommon case of "some dependent library's
header files have been installed somewhere other than in
a system include directory". Is it possible to get meson to do
things the more standard way, where if a binary has a dependency
declared then the CFLAGS for that dependency get used for all
objects that go into it?
This *is* what Meson does, it's QEMU that has always done non-standard
things in order to share the .o files for target-independent sources.
Back in the day is was -Wl,--whole-archive, then it became foo-obj-y.
Now it's foo_ss but it's the same thing as foo-obj-y in the end.
Once the relation between objects and binaries becomes many-to-many, you
can't really apply "the CFLAGS for the binaries' dependencies" to all
the objects. Pre-Meson, there were three ways to declare dependencies:
- placing pkg-config output directly in $(QEMU_CFLAGS) and $(LIBS).
This caused binaries to have unnecessary dependencies at times.
- mentioning dependencies in $(obj)/foo.o_{CFLAGS,LIBS} or something
like that, declaring dependencies in objects and applying them to
binaries. The Makefile implementation was very buggy.
- a mix of the two, with the include path added to QEMU_CFLAGS and a
target variable definition "foo$(EXESUF): LIBS += ..." that avoided the
unnecessary dependencies.
The sourceset thing was added to Meson specifically for QEMU, inspired
by the second option. Without the bugs[1], everything could become
fine-grained. Only glib stayed in QEMU_CFLAGS (the third option);
anything else was unnecessary because everything includes glib.h through
osdep.h anyway.
The closest thing to what you're suggesting is to keep LIBS fine-grained
while making CFLAGS coarse-grained, i.e. the third option above. That
is what the patches I sent today do when moving the glib tests to Meson,
so it is not hard to expand it to other dependencies; but while it might
avoid the gnutls issues, it will probably cause other issues---think of
SDL messing with "#define main". Overall, I'm not sure it's a win.
Thanks,
Paolo
[1] there is the gnutls issue on macOS, but IIRC the dependency CFLAGS
are just the manifestation of a bug somewhere else that I forgot the
details about (the Meson issue tracker and wiki page has the info, I'll
get back to it some day). This bug only affects gnutls because we do
tend to "#include <>" in .c files only, and did so even before the
switch to Meson.
