Eduardo Habkost <ehabk...@redhat.com> writes:
> On Thu, Oct 01, 2020 at 04:41:52PM +0200, Philippe Mathieu-Daudé wrote:
>> Only qemu-system-FOO and qemu-storage-daemon provide QMP
>> monitors, therefore such declarations and definitions are
>> irrelevant for user-mode emulation.
>>
>> Restricting the x86-specific commands to machine-target.json
>> pulls less QAPI-generated code into user-mode.
>
> Is this still true without "qapi: Restrict code generated for
> user-mode"?
>
> Markus, Eric: what's the difference between machine.json and
> machine-target.json? commit 7f7b4e7abef4 ("qapi: Split
> machine-target.json off target.json and misc.json") explains what
> but not why.
My bad.
Short explanation: machine-target.json can use preprocessor symbols with
'if' that are only available in target-specific code: TARGET_S390X,
TARGET_I386, TARGET_ARM, ... This requires compiling per target.
machine.json can't use these, because it's compiled just once.
Same for misc-target.json and misc.json.
Now the long explanation.
The clue is buried in the patch:
diff --git a/qapi/Makefile.objs b/qapi/Makefile.objs
index 01dced01aa..4e87bef6e1 100644
--- a/qapi/Makefile.objs
+++ b/qapi/Makefile.objs
@@ -9,7 +9,7 @@ QAPI_COMMON_MODULES = audio authz block-core block char
common crypto
QAPI_COMMON_MODULES += introspect job machine migration misc net
QAPI_COMMON_MODULES += qdev qom rdma rocker run-state sockets tpm
QAPI_COMMON_MODULES += trace transaction ui
-QAPI_TARGET_MODULES = target
+QAPI_TARGET_MODULES = machine-target target
QAPI_MODULES = $(QAPI_COMMON_MODULES) $(QAPI_TARGET_MODULES)
util-obj-y += qapi-builtin-types.o
QAPI_TARGET_MODULES appears in commit 61eb9e80d5:
qapi: New module target.json
We can't add appropriate target-specific conditionals to misc.json,
because that would make all of misc.json unusable in
target-independent code. To keep misc.json target-independent, we
need to split off target-dependent target.json.
This commit doesn't actually split off anything, it merely creates the
empty module. The next few patches will move stuff from misc.json
there.
Signed-off-by: Markus Armbruster <arm...@redhat.com>
Aha: it's about compiling per target, to make target-specific
conditionals available.
This part of qapi/Makefile.objs has since morphed into
qapi_inputs = []
qapi_specific_outputs = []
foreach module : qapi_all_modules
qapi_inputs += [ files(module + '.json') ]
qapi_module_outputs = [
...
]
if module.endswith('-target')
qapi_specific_outputs += qapi_module_outputs
else
qapi_util_outputs += qapi_module_outputs
endif
endforeach
in qapi/meson.build. Further down:
# Now go through all the outputs and add them to the right sourceset.
# These loops must be synchronized with the output of the above custom
target.
i = 0
foreach output : qapi_util_outputs
if output.endswith('.h')
genh += qapi_files[i]
endif
util_ss.add(qapi_files[i])
i = i + 1
endforeach
foreach output : qapi_specific_outputs + qapi_nonmodule_outputs
if output.endswith('.h')
genh += qapi_files[i]
endif
specific_ss.add(when: 'CONFIG_SOFTMMU', if_true: qapi_files[i])
i = i + 1
endforeach
The source files generated for the "common" modules are added to
sourceset util_ss, and the ones for the "target" modules are added to
sourceset specific_ss.
The former gets compiled just once, and the .o get linked into pretty
much everything.
The latter gets compiled per target, and the .o get linked into
target-specific executables.
Clear as mud?
[...]
