arm64: kernel/sys.c - silence initialization warnings.

Building arch/arm64/kernel/sys.o with W=1 throws over 300 warnings:

/usr/src/linux-next/arch/arm64/kernel/sys.c:56:40: warning: initialized field overwritten [-Woverride-init]
56 | #define __SYSCALL(nr, sym) [nr] = __arm64_##sym,
| ^~~~~~~~
/usr/src/linux-next/include/uapi/asm-generic/unistd.h:29:37: note: in expansion of macro '__SYSCALL'
29 | #define __SC_COMP(_nr, _sys, _comp) __SYSCALL(_nr, _sys)
| ^~~~~~~~~
/usr/src/linux-next/include/uapi/asm-generic/unistd.h:34:1: note: in expansion of macro '__SC_COMP'
34 | __SC_COMP(__NR_io_setup, sys_io_setup, compat_sys_io_setup)

      | ^~~~~~~~~

We know that's pretty much the file's purpose in life, so tell the build system to not remind us. This makes the 1 other warning a lot more noticeable.

index ed65576ce710..916b21d2b35b 100644
@@ -8,6 +8,7 @@ CFLAGS_armv8_deprecated.o := -I$(src)
 CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_insn.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
+CFLAGS_sys.o += $(call cc-disable-warning, override-init)
 
 # Object file lists.
 obj-y			:= debug-monitors.o entry.o irq.o fpsimd.o		\

Please just remove the override-init warning, it is not helpful at all.

The tl;dr: Christoph is *probably* correct that it's not flagging any actual bugs. And since *my* interest is "get the kernel tree to a point where W=1 or sparse throwing a warning is something worth looking at", I'm not opposed to a patch to remove it from W=1 tree-wide if it has essentially zero chance of flagging an actual bug.

The longer version:

So I did a quick analysis...

For an x86_64 allmodconfig, there's not that many left:

     16 drivers/ata/ahci.h
      1 drivers/ata/pata_atiixp.c
      1 drivers/ata/pata_cs5520.c
      1 drivers/ata/pata_cs5530.c
      1 drivers/ata/pata_sc1200.c
      1 drivers/ata/pata_serverworks.c
      1 drivers/ata/sata_mv.c
      4 drivers/ata/sata_nv.c
      1 drivers/ata/sata_sil24.c
      1 drivers/block/drbd/drbd_main.c
      6 drivers/gpu/drm/amd/amdgpu/../include/asic_reg/dce/dce_6_0_d.h
      2 drivers/gpu/drm/amd/amdgpu/../include/asic_reg/dce/dce_6_0_sh_mask.h
      1 drivers/input/serio/i8042-x86ia64io.h
      1 include/linux/blkdev.h
      1 kernel/bpf/btf.c
      4 kernel/time/hrtimer.c
      1 lib/errname.c

The drivers/ata *.c warnings all appear to be the same type of thing:

static struct scsi_host_template serverworks_osb4_sht = {
ATA_BMDMA_SHT(DRV_NAME),
.sg_tablesize = LIBATA_DUMB_MAX_PRD,
};

The preprocessor macro defining the struct contents, and then overriding one predefined value. So that's half of x64_64 done right there.

There's a few corners still need looking at, like why drivers/ata/ahci.h throws 16 warnings on x64, but 30 on arm and 28 on arm64, and why there's 4 warnings on include/linux/stddef.h on arm64 but not arm or x86.

But the number is certainly small enough that it's only a day or two's work at most to check every single one. If I go through the rest of x86 and arm and they're all legit, I'll send a patch to nuke it kernel-wide rather than piecemeal.