On Wed, Jul 15, 2020 at 2:07 PM Lee Jones <[email protected]> wrote: > > On Wed, 15 Jul 2020, Lee Jones wrote: > > > On Wed, 15 Jul 2020, Rafael J. Wysocki wrote: > > > > > On Wed, Jul 15, 2020 at 1:34 PM Lee Jones <[email protected]> wrote: > > > > > > > > On Wed, 15 Jul 2020, Rafael J. Wysocki wrote: > > > > > > > > > On Wed, Jul 15, 2020 at 5:27 AM Viresh Kumar > > > > > <[email protected]> wrote: > > > > > > > > > > > > On 15-07-20, 08:54, Viresh Kumar wrote: > > > > > > > On 14-07-20, 22:03, Lee Jones wrote: > > > > > > > > On Tue, 14 Jul 2020, Rafael J. Wysocki wrote: > > > > > > > > > > > > > > > > > On Tue, Jul 14, 2020 at 4:51 PM Lee Jones > > > > > > > > > <[email protected]> wrote: > > > > > > > > > > > > > > > > > > > > Can't see them being used anywhere and the compiler doesn't > > > > > > > > > > complain > > > > > > > > > > that they're missing, so ... > > > > > > > > > > > > > > > > > > Aren't they needed for automatic module loading in certain > > > > > > > > > configurations? > > > > > > > > > > > > > > > > Any idea how that works, or where the code is for that? > > > > > > > > > > > > > > The MODULE_DEVICE_TABLE() thingy creates a map of vendor-id, > > > > > > > product-id that the kernel keeps after boot (and so there is no > > > > > > > static > > > > > > > reference of it for the compiler), later when a device is > > > > > > > hotplugged > > > > > > > into the kernel it refers to the map to find the related driver > > > > > > > for it > > > > > > > and loads it if it isn't already loaded. > > > > > > > > > > > > > > This has some of it, search for MODULE_DEVICE_TABLE() in it. > > > > > > > Documentation/driver-api/usb/hotplug.rst > > > > > > > > > > > > And you just need to add __maybe_unused to them to suppress the > > > > > > warning. > > > > > > > > > > Wouldn't that cause the compiler to optimize them away if it doesn't > > > > > see any users? > > > > > > > > It looks like they're only unused when !MODULE, > > > > > > OK > > > > > > > in which case optimising them away would be the correct thing to do, no? > > > > It would be good if someone with a little more knowledge could provide > > a second opinion though. I would think (hope) that the compiler would > > be smart enough to see when its actually in use. After all, it is the > > compiler that places the information into the device table. > > > > If that is not the case, then the MODULE_DEVICE_TABLE() magic is > > broken and will need fixing. Removing boiler-plate is good, but not > > at the expense of obfuscation. > > Okay, I'm satisfied. This test build is without __maybe_unused: > > # All configs built as modules (MODULE) - the compiler knows to use the tables > > $ ccache make -f Makefile -j24 KBUILD_OUTPUT=../builds/build-x86 allmodconfig > $ ccache make -f Makefile -j24 KBUILD_OUTPUT=../builds/build-x86 W=1 > drivers/cpufreq/ > [...] > CC [M] drivers/cpufreq/pcc-cpufreq.o > > # All configs built-in (!MODULE) - the compiler sees that they are unused > > $ ccache make -f Makefile -j24 KBUILD_OUTPUT=../builds/build-x86 allyesconfig > $ ccache make -f Makefile -j24 KBUILD_OUTPUT=../builds/build-x86 W=1 > drivers/cpufreq/ > CC drivers/cpufreq/pcc-cpufreq.o > drivers/cpufreq/pcc-cpufreq.c:619:36: warning: ‘processor_device_ids’ > defined but not used [-Wunused-const-variable=] > 619 | static const struct acpi_device_id processor_device_ids[] = { > | ^~~~~~~~~~~~~~~~~~~~ >
OK I thought that this would be the case. :-)
