trivial script to find unused CONFIG_<FOO> uses in #ifdef blocks

[Joe Perches <joe@perches.com>]

A kernel janitorial task could be to remove blocks of code like:

	#ifdef CONFIG_<FOO>
		...
	#endif

where the config <FOO> symbol is not used in any Kconfig file.

Here is a trivial script to find these apparently unused Kconfig entries
that are in #ifdef CONFIG_<FOO> blocks and its current output of -next.

An example removal is: https://lore.kernel.org/lkml/997c0cdbd57752252d87129185a973c7d42e491f.camel@perches.com/T/#u

Be aware that some of the entries below are false positives.

For instance 1:
	CONFIG_X86_X32_ABI which is defined and exported in
	arch/x86/Makefile:export CONFIG_X86_X32_ABI

And it's possible other entries are typos of actual Kconfig symbols.

For instance 2:
	CONFIG_CPU_HAS_FP is likely a typo of CONFIG_CPU_HAS_FPU

	arch/csky/kernel/traps.c:#ifdef CONFIG_CPU_HAS_FPU
	arch/csky/kernel/traps.c:#ifdef CONFIG_CPU_HAS_FPU
	arch/csky/kernel/traps.c:#ifdef CONFIG_CPU_HAS_FP
	arch/csky/kernel/traps.c:#ifdef CONFIG_CPU_HAS_FP

But some of the referenced #ifdef blocks in the kernel source tree
could be completely removed.

Some of these entries are leftovers from code that once was enabled,
others are just entries that were never possible to enable.

$ git grep -P '^\s*#\s*if(?:def\s+|\s+defined\s*\(?\s*)CONFIG_[A-Z0-9_]+' | \
  grep -oh -P '\bCONFIG_[A-Z0-9_]+\b' | \
  sort | sed -e 's/^CONFIG_//' -e 's/_MODULE$//' | uniq | \
  while read config ; do \
    echo CONFIG_$config; \
    git grep -w $config -- '*/Kconfig*' | \
    wc -l; \
  done | \
  grep -B1 '^0'
CONFIG_ACORNSCSI_CONSTANTS
0
--
CONFIG_AS_CFI_VAL_OFFSET
0
--
CONFIG_ASYNC_TX_CHANNEL_SWITCH
0
--
CONFIG_B43_PCMCIA
0
--
CONFIG_BAND_CBAND
0
CONFIG_BAND_LBAND
0
CONFIG_BAND_SBAND
0
CONFIG_BAND_UHF
0
CONFIG_BAND_VHF
0
--
CONFIG_CAAM_QI
0
--
CONFIG_COMET_EARLY_UART_DEBUG
0
--
CONFIG_CPU_H300H
0
--
CONFIG_CPU_HAS_FP
0
--
CONFIG_CPU_SUBTYPE_ST40
0
--
CONFIG_DBX500_PRCMU_QOS_POWER
0
--
CONFIG_DEBUG_LL_SER3
0
--
CONFIG_DEBUG_SHIRQ_FIXME
0
--
CONFIG_DEBUG_ZTE_ZX
0
--
CONFIG_DIO_CONSTANTS
0
--
CONFIG_DRM_AMD_DC_DMUB
0
--
CONFIG_EXTRA_DEBUG_CHECKS
0
--
CONFIG_FSCACHE_OBJECT_LIST
0
--
CONFIG_FSL_DPA_PIRQ_FAST
0
CONFIG_FSL_DPA_PIRQ_SLOW
0
--
CONFIG_FUSION_MAX_FC_SGE
0
--
CONFIG_HP_HOOK_WORKAROUND
0
--
CONFIG_IEEE80211_DEBUG
0
--
CONFIG_IMX_GPT_ICAP
0
--
CONFIG_IPX_INTERN
0
CONFIG_IRDA
0
--
CONFIG_LMC_IGNORE_HARDWARE_HANDSHAKE
0
--
CONFIG_MY_KUNIT_TEST
0
--
CONFIG_NCR53C8XX_PREFETCH
0
--
CONFIG_NET_FUNKINESS
0
--
CONFIG_NILFS_POSIX_ACL
0
CONFIG_NILFS_XATTR
0
--
CONFIG_NOUVEAU_I2C_INTERNAL
0
--
CONFIG_OLPC_XO1_5_SCI
0
--
CONFIG_OPEN_FPU_DZE
0
CONFIG_OPEN_FPU_IDE
0
CONFIG_OPEN_FPU_IOE
0
CONFIG_OPEN_FPU_IXE
0
CONFIG_OPEN_FPU_OFE
0
CONFIG_OPEN_FPU_UFE
0
--
CONFIG_PAGE_SIZE_1MB
0
--
CONFIG_PINCTRL_DB8540
0
--
CONFIG_PM_SUSPEND
0
--
CONFIG_PPC_EARLY_DEBUG_MICROWATT
0
--
CONFIG_PXA_FICP
0
--
CONFIG_SA1100_CT6001
0
--
CONFIG_SBMAC_COALESCE
0
--
CONFIG_SCSI_NCR53C8XX_DISABLE_MPARITY_CHECK
0
CONFIG_SCSI_NCR53C8XX_DISABLE_PARITY_CHECK
0
CONFIG_SCSI_NCR53C8XX_FORCE_SYNC_NEGO
0
CONFIG_SCSI_NCR53C8XX_IARB
0
CONFIG_SCSI_NCR53C8XX_INTEGRITY_CHECK
0
--
CONFIG_SCSI_NCR53C8XX_NO_WORD_TRANSFERS
0
--
CONFIG_SGI_IP35
0
--
CONFIG_SOC_SAMA7
0
--
CONFIG_SOMETHING
0
--
CONFIG_SSB_DEBUG
0
--
CONFIG_STANDARD_DAB
0
CONFIG_STANDARD_DVBT
0
--
CONFIG_SYS_ISDBT
0
--
CONFIG_TASKS_RCU_TRACE
0
--
CONFIG_TUNER_DIB0090_P1B_SUPPORT
0
--
CONFIG_UM
0
--
CONFIG_WD33C93_PIO
0
--
CONFIG_X86_X32_ABI
0