unix: add consts for ELF handling

This adds a few constants that help to handle ELF files and coredumps.

Change-Id: Ifd4c1bd4c8839065af4233ccbf42964a8e96fdf8
Reviewed-on: https://go-review.googlesource.com/c/sys/+/713980
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Auto-Submit: Sean Liao <sean@liao.dev>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
diff --git a/unix/mkerrors.sh b/unix/mkerrors.sh
index d1c8b26..4251707 100755
--- a/unix/mkerrors.sh
+++ b/unix/mkerrors.sh
@@ -226,6 +226,7 @@
 #include <linux/cryptouser.h>
 #include <linux/devlink.h>
 #include <linux/dm-ioctl.h>
+#include <linux/elf.h>
 #include <linux/errqueue.h>
 #include <linux/ethtool_netlink.h>
 #include <linux/falloc.h>
@@ -529,6 +530,7 @@
 		$2 ~ /^O[CNPFPL][A-Z]+[^_][A-Z]+$/ ||
 		$2 ~ /^(NL|CR|TAB|BS|VT|FF)DLY$/ ||
 		$2 ~ /^(NL|CR|TAB|BS|VT|FF)[0-9]$/ ||
+		$2 ~ /^(DT|EI|ELF|EV|NN|NT|PF|SHF|SHN|SHT|STB|STT|VER)_/ ||
 		$2 ~ /^O?XTABS$/ ||
 		$2 ~ /^TC[IO](ON|OFF)$/ ||
 		$2 ~ /^IN_/ ||
diff --git a/unix/zerrors_linux.go b/unix/zerrors_linux.go
index b6db27d..d0a75da 100644
--- a/unix/zerrors_linux.go
+++ b/unix/zerrors_linux.go
@@ -853,20 +853,86 @@
 	DM_VERSION_MAJOR                            = 0x4
 	DM_VERSION_MINOR                            = 0x32
 	DM_VERSION_PATCHLEVEL                       = 0x0
+	DT_ADDRRNGHI                                = 0x6ffffeff
+	DT_ADDRRNGLO                                = 0x6ffffe00
 	DT_BLK                                      = 0x6
 	DT_CHR                                      = 0x2
+	DT_DEBUG                                    = 0x15
 	DT_DIR                                      = 0x4
+	DT_ENCODING                                 = 0x20
 	DT_FIFO                                     = 0x1
+	DT_FINI                                     = 0xd
+	DT_FLAGS_1                                  = 0x6ffffffb
+	DT_GNU_HASH                                 = 0x6ffffef5
+	DT_HASH                                     = 0x4
+	DT_HIOS                                     = 0x6ffff000
+	DT_HIPROC                                   = 0x7fffffff
+	DT_INIT                                     = 0xc
+	DT_JMPREL                                   = 0x17
 	DT_LNK                                      = 0xa
+	DT_LOOS                                     = 0x6000000d
+	DT_LOPROC                                   = 0x70000000
+	DT_NEEDED                                   = 0x1
+	DT_NULL                                     = 0x0
+	DT_PLTGOT                                   = 0x3
+	DT_PLTREL                                   = 0x14
+	DT_PLTRELSZ                                 = 0x2
 	DT_REG                                      = 0x8
+	DT_REL                                      = 0x11
+	DT_RELA                                     = 0x7
+	DT_RELACOUNT                                = 0x6ffffff9
+	DT_RELAENT                                  = 0x9
+	DT_RELASZ                                   = 0x8
+	DT_RELCOUNT                                 = 0x6ffffffa
+	DT_RELENT                                   = 0x13
+	DT_RELSZ                                    = 0x12
+	DT_RPATH                                    = 0xf
 	DT_SOCK                                     = 0xc
+	DT_SONAME                                   = 0xe
+	DT_STRSZ                                    = 0xa
+	DT_STRTAB                                   = 0x5
+	DT_SYMBOLIC                                 = 0x10
+	DT_SYMENT                                   = 0xb
+	DT_SYMTAB                                   = 0x6
+	DT_TEXTREL                                  = 0x16
 	DT_UNKNOWN                                  = 0x0
+	DT_VALRNGHI                                 = 0x6ffffdff
+	DT_VALRNGLO                                 = 0x6ffffd00
+	DT_VERDEF                                   = 0x6ffffffc
+	DT_VERDEFNUM                                = 0x6ffffffd
+	DT_VERNEED                                  = 0x6ffffffe
+	DT_VERNEEDNUM                               = 0x6fffffff
+	DT_VERSYM                                   = 0x6ffffff0
 	DT_WHT                                      = 0xe
 	ECHO                                        = 0x8
 	ECRYPTFS_SUPER_MAGIC                        = 0xf15f
 	EFD_SEMAPHORE                               = 0x1
 	EFIVARFS_MAGIC                              = 0xde5e81e4
 	EFS_SUPER_MAGIC                             = 0x414a53
+	EI_CLASS                                    = 0x4
+	EI_DATA                                     = 0x5
+	EI_MAG0                                     = 0x0
+	EI_MAG1                                     = 0x1
+	EI_MAG2                                     = 0x2
+	EI_MAG3                                     = 0x3
+	EI_NIDENT                                   = 0x10
+	EI_OSABI                                    = 0x7
+	EI_PAD                                      = 0x8
+	EI_VERSION                                  = 0x6
+	ELFCLASS32                                  = 0x1
+	ELFCLASS64                                  = 0x2
+	ELFCLASSNONE                                = 0x0
+	ELFCLASSNUM                                 = 0x3
+	ELFDATA2LSB                                 = 0x1
+	ELFDATA2MSB                                 = 0x2
+	ELFDATANONE                                 = 0x0
+	ELFMAG                                      = "\177ELF"
+	ELFMAG0                                     = 0x7f
+	ELFMAG1                                     = 'E'
+	ELFMAG2                                     = 'L'
+	ELFMAG3                                     = 'F'
+	ELFOSABI_LINUX                              = 0x3
+	ELFOSABI_NONE                               = 0x0
 	EM_386                                      = 0x3
 	EM_486                                      = 0x6
 	EM_68K                                      = 0x4
@@ -1152,14 +1218,24 @@
 	ETH_P_WCCP                                  = 0x883e
 	ETH_P_X25                                   = 0x805
 	ETH_P_XDSA                                  = 0xf8
+	ET_CORE                                     = 0x4
+	ET_DYN                                      = 0x3
+	ET_EXEC                                     = 0x2
+	ET_HIPROC                                   = 0xffff
+	ET_LOPROC                                   = 0xff00
+	ET_NONE                                     = 0x0
+	ET_REL                                      = 0x1
 	EV_ABS                                      = 0x3
 	EV_CNT                                      = 0x20
+	EV_CURRENT                                  = 0x1
 	EV_FF                                       = 0x15
 	EV_FF_STATUS                                = 0x17
 	EV_KEY                                      = 0x1
 	EV_LED                                      = 0x11
 	EV_MAX                                      = 0x1f
 	EV_MSC                                      = 0x4
+	EV_NONE                                     = 0x0
+	EV_NUM                                      = 0x2
 	EV_PWR                                      = 0x16
 	EV_REL                                      = 0x2
 	EV_REP                                      = 0x14
@@ -2276,7 +2352,167 @@
 	NLM_F_REPLACE                               = 0x100
 	NLM_F_REQUEST                               = 0x1
 	NLM_F_ROOT                                  = 0x100
+	NN_386_IOPERM                               = "LINUX"
+	NN_386_TLS                                  = "LINUX"
+	NN_ARC_V2                                   = "LINUX"
+	NN_ARM_FPMR                                 = "LINUX"
+	NN_ARM_GCS                                  = "LINUX"
+	NN_ARM_HW_BREAK                             = "LINUX"
+	NN_ARM_HW_WATCH                             = "LINUX"
+	NN_ARM_PACA_KEYS                            = "LINUX"
+	NN_ARM_PACG_KEYS                            = "LINUX"
+	NN_ARM_PAC_ENABLED_KEYS                     = "LINUX"
+	NN_ARM_PAC_MASK                             = "LINUX"
+	NN_ARM_POE                                  = "LINUX"
+	NN_ARM_SSVE                                 = "LINUX"
+	NN_ARM_SVE                                  = "LINUX"
+	NN_ARM_SYSTEM_CALL                          = "LINUX"
+	NN_ARM_TAGGED_ADDR_CTRL                     = "LINUX"
+	NN_ARM_TLS                                  = "LINUX"
+	NN_ARM_VFP                                  = "LINUX"
+	NN_ARM_ZA                                   = "LINUX"
+	NN_ARM_ZT                                   = "LINUX"
+	NN_AUXV                                     = "CORE"
+	NN_FILE                                     = "CORE"
+	NN_GNU_PROPERTY_TYPE_0                      = "GNU"
+	NN_LOONGARCH_CPUCFG                         = "LINUX"
+	NN_LOONGARCH_CSR                            = "LINUX"
+	NN_LOONGARCH_HW_BREAK                       = "LINUX"
+	NN_LOONGARCH_HW_WATCH                       = "LINUX"
+	NN_LOONGARCH_LASX                           = "LINUX"
+	NN_LOONGARCH_LBT                            = "LINUX"
+	NN_LOONGARCH_LSX                            = "LINUX"
+	NN_MIPS_DSP                                 = "LINUX"
+	NN_MIPS_FP_MODE                             = "LINUX"
+	NN_MIPS_MSA                                 = "LINUX"
+	NN_PPC_DEXCR                                = "LINUX"
+	NN_PPC_DSCR                                 = "LINUX"
+	NN_PPC_EBB                                  = "LINUX"
+	NN_PPC_HASHKEYR                             = "LINUX"
+	NN_PPC_PKEY                                 = "LINUX"
+	NN_PPC_PMU                                  = "LINUX"
+	NN_PPC_PPR                                  = "LINUX"
+	NN_PPC_SPE                                  = "LINUX"
+	NN_PPC_TAR                                  = "LINUX"
+	NN_PPC_TM_CDSCR                             = "LINUX"
+	NN_PPC_TM_CFPR                              = "LINUX"
+	NN_PPC_TM_CGPR                              = "LINUX"
+	NN_PPC_TM_CPPR                              = "LINUX"
+	NN_PPC_TM_CTAR                              = "LINUX"
+	NN_PPC_TM_CVMX                              = "LINUX"
+	NN_PPC_TM_CVSX                              = "LINUX"
+	NN_PPC_TM_SPR                               = "LINUX"
+	NN_PPC_VMX                                  = "LINUX"
+	NN_PPC_VSX                                  = "LINUX"
+	NN_PRFPREG                                  = "CORE"
+	NN_PRPSINFO                                 = "CORE"
+	NN_PRSTATUS                                 = "CORE"
+	NN_PRXFPREG                                 = "LINUX"
+	NN_RISCV_CSR                                = "LINUX"
+	NN_RISCV_TAGGED_ADDR_CTRL                   = "LINUX"
+	NN_RISCV_VECTOR                             = "LINUX"
+	NN_S390_CTRS                                = "LINUX"
+	NN_S390_GS_BC                               = "LINUX"
+	NN_S390_GS_CB                               = "LINUX"
+	NN_S390_HIGH_GPRS                           = "LINUX"
+	NN_S390_LAST_BREAK                          = "LINUX"
+	NN_S390_PREFIX                              = "LINUX"
+	NN_S390_PV_CPU_DATA                         = "LINUX"
+	NN_S390_RI_CB                               = "LINUX"
+	NN_S390_SYSTEM_CALL                         = "LINUX"
+	NN_S390_TDB                                 = "LINUX"
+	NN_S390_TIMER                               = "LINUX"
+	NN_S390_TODCMP                              = "LINUX"
+	NN_S390_TODPREG                             = "LINUX"
+	NN_S390_VXRS_HIGH                           = "LINUX"
+	NN_S390_VXRS_LOW                            = "LINUX"
+	NN_SIGINFO                                  = "CORE"
+	NN_TASKSTRUCT                               = "CORE"
+	NN_VMCOREDD                                 = "LINUX"
+	NN_X86_SHSTK                                = "LINUX"
+	NN_X86_XSAVE_LAYOUT                         = "LINUX"
+	NN_X86_XSTATE                               = "LINUX"
 	NSFS_MAGIC                                  = 0x6e736673
+	NT_386_IOPERM                               = 0x201
+	NT_386_TLS                                  = 0x200
+	NT_ARC_V2                                   = 0x600
+	NT_ARM_FPMR                                 = 0x40e
+	NT_ARM_GCS                                  = 0x410
+	NT_ARM_HW_BREAK                             = 0x402
+	NT_ARM_HW_WATCH                             = 0x403
+	NT_ARM_PACA_KEYS                            = 0x407
+	NT_ARM_PACG_KEYS                            = 0x408
+	NT_ARM_PAC_ENABLED_KEYS                     = 0x40a
+	NT_ARM_PAC_MASK                             = 0x406
+	NT_ARM_POE                                  = 0x40f
+	NT_ARM_SSVE                                 = 0x40b
+	NT_ARM_SVE                                  = 0x405
+	NT_ARM_SYSTEM_CALL                          = 0x404
+	NT_ARM_TAGGED_ADDR_CTRL                     = 0x409
+	NT_ARM_TLS                                  = 0x401
+	NT_ARM_VFP                                  = 0x400
+	NT_ARM_ZA                                   = 0x40c
+	NT_ARM_ZT                                   = 0x40d
+	NT_AUXV                                     = 0x6
+	NT_FILE                                     = 0x46494c45
+	NT_GNU_PROPERTY_TYPE_0                      = 0x5
+	NT_LOONGARCH_CPUCFG                         = 0xa00
+	NT_LOONGARCH_CSR                            = 0xa01
+	NT_LOONGARCH_HW_BREAK                       = 0xa05
+	NT_LOONGARCH_HW_WATCH                       = 0xa06
+	NT_LOONGARCH_LASX                           = 0xa03
+	NT_LOONGARCH_LBT                            = 0xa04
+	NT_LOONGARCH_LSX                            = 0xa02
+	NT_MIPS_DSP                                 = 0x800
+	NT_MIPS_FP_MODE                             = 0x801
+	NT_MIPS_MSA                                 = 0x802
+	NT_PPC_DEXCR                                = 0x111
+	NT_PPC_DSCR                                 = 0x105
+	NT_PPC_EBB                                  = 0x106
+	NT_PPC_HASHKEYR                             = 0x112
+	NT_PPC_PKEY                                 = 0x110
+	NT_PPC_PMU                                  = 0x107
+	NT_PPC_PPR                                  = 0x104
+	NT_PPC_SPE                                  = 0x101
+	NT_PPC_TAR                                  = 0x103
+	NT_PPC_TM_CDSCR                             = 0x10f
+	NT_PPC_TM_CFPR                              = 0x109
+	NT_PPC_TM_CGPR                              = 0x108
+	NT_PPC_TM_CPPR                              = 0x10e
+	NT_PPC_TM_CTAR                              = 0x10d
+	NT_PPC_TM_CVMX                              = 0x10a
+	NT_PPC_TM_CVSX                              = 0x10b
+	NT_PPC_TM_SPR                               = 0x10c
+	NT_PPC_VMX                                  = 0x100
+	NT_PPC_VSX                                  = 0x102
+	NT_PRFPREG                                  = 0x2
+	NT_PRPSINFO                                 = 0x3
+	NT_PRSTATUS                                 = 0x1
+	NT_PRXFPREG                                 = 0x46e62b7f
+	NT_RISCV_CSR                                = 0x900
+	NT_RISCV_TAGGED_ADDR_CTRL                   = 0x902
+	NT_RISCV_VECTOR                             = 0x901
+	NT_S390_CTRS                                = 0x304
+	NT_S390_GS_BC                               = 0x30c
+	NT_S390_GS_CB                               = 0x30b
+	NT_S390_HIGH_GPRS                           = 0x300
+	NT_S390_LAST_BREAK                          = 0x306
+	NT_S390_PREFIX                              = 0x305
+	NT_S390_PV_CPU_DATA                         = 0x30e
+	NT_S390_RI_CB                               = 0x30d
+	NT_S390_SYSTEM_CALL                         = 0x307
+	NT_S390_TDB                                 = 0x308
+	NT_S390_TIMER                               = 0x301
+	NT_S390_TODCMP                              = 0x302
+	NT_S390_TODPREG                             = 0x303
+	NT_S390_VXRS_HIGH                           = 0x30a
+	NT_S390_VXRS_LOW                            = 0x309
+	NT_SIGINFO                                  = 0x53494749
+	NT_TASKSTRUCT                               = 0x4
+	NT_VMCOREDD                                 = 0x700
+	NT_X86_SHSTK                                = 0x204
+	NT_X86_XSAVE_LAYOUT                         = 0x205
+	NT_X86_XSTATE                               = 0x202
 	OCFS2_SUPER_MAGIC                           = 0x7461636f
 	OCRNL                                       = 0x8
 	OFDEL                                       = 0x80
@@ -2463,6 +2699,59 @@
 	PERF_RECORD_MISC_USER                       = 0x2
 	PERF_SAMPLE_BRANCH_PLM_ALL                  = 0x7
 	PERF_SAMPLE_WEIGHT_TYPE                     = 0x1004000
+	PF_ALG                                      = 0x26
+	PF_APPLETALK                                = 0x5
+	PF_ASH                                      = 0x12
+	PF_ATMPVC                                   = 0x8
+	PF_ATMSVC                                   = 0x14
+	PF_AX25                                     = 0x3
+	PF_BLUETOOTH                                = 0x1f
+	PF_BRIDGE                                   = 0x7
+	PF_CAIF                                     = 0x25
+	PF_CAN                                      = 0x1d
+	PF_DECnet                                   = 0xc
+	PF_ECONET                                   = 0x13
+	PF_FILE                                     = 0x1
+	PF_IB                                       = 0x1b
+	PF_IEEE802154                               = 0x24
+	PF_INET                                     = 0x2
+	PF_INET6                                    = 0xa
+	PF_IPX                                      = 0x4
+	PF_IRDA                                     = 0x17
+	PF_ISDN                                     = 0x22
+	PF_IUCV                                     = 0x20
+	PF_KCM                                      = 0x29
+	PF_KEY                                      = 0xf
+	PF_LLC                                      = 0x1a
+	PF_LOCAL                                    = 0x1
+	PF_MAX                                      = 0x2e
+	PF_MCTP                                     = 0x2d
+	PF_MPLS                                     = 0x1c
+	PF_NETBEUI                                  = 0xd
+	PF_NETLINK                                  = 0x10
+	PF_NETROM                                   = 0x6
+	PF_NFC                                      = 0x27
+	PF_PACKET                                   = 0x11
+	PF_PHONET                                   = 0x23
+	PF_PPPOX                                    = 0x18
+	PF_QIPCRTR                                  = 0x2a
+	PF_R                                        = 0x4
+	PF_RDS                                      = 0x15
+	PF_ROSE                                     = 0xb
+	PF_ROUTE                                    = 0x10
+	PF_RXRPC                                    = 0x21
+	PF_SECURITY                                 = 0xe
+	PF_SMC                                      = 0x2b
+	PF_SNA                                      = 0x16
+	PF_TIPC                                     = 0x1e
+	PF_UNIX                                     = 0x1
+	PF_UNSPEC                                   = 0x0
+	PF_VSOCK                                    = 0x28
+	PF_W                                        = 0x2
+	PF_WANPIPE                                  = 0x19
+	PF_X                                        = 0x1
+	PF_X25                                      = 0x9
+	PF_XDP                                      = 0x2c
 	PID_FS_MAGIC                                = 0x50494446
 	PIPEFS_MAGIC                                = 0x50495045
 	PPPIOCGNPMODE                               = 0xc008744c
@@ -2758,6 +3047,23 @@
 	PTRACE_SYSCALL_INFO_NONE                    = 0x0
 	PTRACE_SYSCALL_INFO_SECCOMP                 = 0x3
 	PTRACE_TRACEME                              = 0x0
+	PT_AARCH64_MEMTAG_MTE                       = 0x70000002
+	PT_DYNAMIC                                  = 0x2
+	PT_GNU_EH_FRAME                             = 0x6474e550
+	PT_GNU_PROPERTY                             = 0x6474e553
+	PT_GNU_RELRO                                = 0x6474e552
+	PT_GNU_STACK                                = 0x6474e551
+	PT_HIOS                                     = 0x6fffffff
+	PT_HIPROC                                   = 0x7fffffff
+	PT_INTERP                                   = 0x3
+	PT_LOAD                                     = 0x1
+	PT_LOOS                                     = 0x60000000
+	PT_LOPROC                                   = 0x70000000
+	PT_NOTE                                     = 0x4
+	PT_NULL                                     = 0x0
+	PT_PHDR                                     = 0x6
+	PT_SHLIB                                    = 0x5
+	PT_TLS                                      = 0x7
 	P_ALL                                       = 0x0
 	P_PGID                                      = 0x2
 	P_PID                                       = 0x1
@@ -3091,6 +3397,47 @@
 	SEEK_MAX                                    = 0x4
 	SEEK_SET                                    = 0x0
 	SELINUX_MAGIC                               = 0xf97cff8c
+	SHF_ALLOC                                   = 0x2
+	SHF_EXCLUDE                                 = 0x8000000
+	SHF_EXECINSTR                               = 0x4
+	SHF_GROUP                                   = 0x200
+	SHF_INFO_LINK                               = 0x40
+	SHF_LINK_ORDER                              = 0x80
+	SHF_MASKOS                                  = 0xff00000
+	SHF_MASKPROC                                = 0xf0000000
+	SHF_MERGE                                   = 0x10
+	SHF_ORDERED                                 = 0x4000000
+	SHF_OS_NONCONFORMING                        = 0x100
+	SHF_RELA_LIVEPATCH                          = 0x100000
+	SHF_RO_AFTER_INIT                           = 0x200000
+	SHF_STRINGS                                 = 0x20
+	SHF_TLS                                     = 0x400
+	SHF_WRITE                                   = 0x1
+	SHN_ABS                                     = 0xfff1
+	SHN_COMMON                                  = 0xfff2
+	SHN_HIPROC                                  = 0xff1f
+	SHN_HIRESERVE                               = 0xffff
+	SHN_LIVEPATCH                               = 0xff20
+	SHN_LOPROC                                  = 0xff00
+	SHN_LORESERVE                               = 0xff00
+	SHN_UNDEF                                   = 0x0
+	SHT_DYNAMIC                                 = 0x6
+	SHT_DYNSYM                                  = 0xb
+	SHT_HASH                                    = 0x5
+	SHT_HIPROC                                  = 0x7fffffff
+	SHT_HIUSER                                  = 0xffffffff
+	SHT_LOPROC                                  = 0x70000000
+	SHT_LOUSER                                  = 0x80000000
+	SHT_NOBITS                                  = 0x8
+	SHT_NOTE                                    = 0x7
+	SHT_NULL                                    = 0x0
+	SHT_NUM                                     = 0xc
+	SHT_PROGBITS                                = 0x1
+	SHT_REL                                     = 0x9
+	SHT_RELA                                    = 0x4
+	SHT_SHLIB                                   = 0xa
+	SHT_STRTAB                                  = 0x3
+	SHT_SYMTAB                                  = 0x2
 	SHUT_RD                                     = 0x0
 	SHUT_RDWR                                   = 0x2
 	SHUT_WR                                     = 0x1
@@ -3317,6 +3664,16 @@
 	STATX_UID                                   = 0x8
 	STATX_WRITE_ATOMIC                          = 0x10000
 	STATX__RESERVED                             = 0x80000000
+	STB_GLOBAL                                  = 0x1
+	STB_LOCAL                                   = 0x0
+	STB_WEAK                                    = 0x2
+	STT_COMMON                                  = 0x5
+	STT_FILE                                    = 0x4
+	STT_FUNC                                    = 0x2
+	STT_NOTYPE                                  = 0x0
+	STT_OBJECT                                  = 0x1
+	STT_SECTION                                 = 0x3
+	STT_TLS                                     = 0x6
 	SYNC_FILE_RANGE_WAIT_AFTER                  = 0x4
 	SYNC_FILE_RANGE_WAIT_BEFORE                 = 0x1
 	SYNC_FILE_RANGE_WRITE                       = 0x2
@@ -3553,6 +3910,8 @@
 	UTIME_OMIT                                  = 0x3ffffffe
 	V9FS_MAGIC                                  = 0x1021997
 	VERASE                                      = 0x2
+	VER_FLG_BASE                                = 0x1
+	VER_FLG_WEAK                                = 0x2
 	VINTR                                       = 0x0
 	VKILL                                       = 0x3
 	VLNEXT                                      = 0xf