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00abdc984b
fq/format/elf/elf.go
Mattias Wadman 502f451cc3 decode: Refactor to use scalar type assert helper
2022-08-08 18:09:49 +02:00

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//nolint:revive
package elf
// https://refspecs.linuxbase.org/elf/gabi4+/contents.html
// https://man7.org/linux/man-pages/man5/elf.5.html
// https://github.com/torvalds/linux/blob/master/include/uapi/linux/elf.h
// TODO: dwarf
import (
"strings"
"github.com/wader/fq/format"
"github.com/wader/fq/pkg/decode"
"github.com/wader/fq/pkg/interp"
"github.com/wader/fq/pkg/scalar"
)
func init() {
interp.RegisterFormat(decode.Format{
Name: format.ELF,
Description: "Executable and Linkable Format",
Groups: []string{format.PROBE},
DecodeFn: elfDecode,
})
}
const (
LITTLE_ENDIAN = 1
BIG_ENDIAN = 2
)
var endianNames = scalar.UToSymStr{
LITTLE_ENDIAN: "little_endian",
BIG_ENDIAN: "big_endian",
}
var classBits = scalar.UToSymU{
1: 32,
2: 64,
}
const (
CLASS_32 = 1
CLASS_64 = 2
)
var osABINames = scalar.UToSymStr{
0: "sysv",
1: "hpux",
2: "netbsd",
3: "linux",
4: "hurd",
5: "86open",
6: "solaris",
7: "monterey",
8: "irix",
9: "freebsd",
10: "tru64",
11: "modesto",
12: "openbsd",
97: "arm",
255: "standalone",
}
var typeNames = scalar.URangeToScalar{
{Range: [2]uint64{0x00, 0x00}, S: scalar.S{Sym: "none"}},
{Range: [2]uint64{0x01, 0x01}, S: scalar.S{Sym: "rel"}},
{Range: [2]uint64{0x02, 0x02}, S: scalar.S{Sym: "exec"}},
{Range: [2]uint64{0x03, 0x03}, S: scalar.S{Sym: "dyn"}},
{Range: [2]uint64{0x04, 0x04}, S: scalar.S{Sym: "core"}},
{Range: [2]uint64{0xfe00, 0xfeff}, S: scalar.S{Sym: "os"}},
{Range: [2]uint64{0xff00, 0xffff}, S: scalar.S{Sym: "proc"}},
}
const (
EM_X86_64 = 0x3e
EM_ARM64 = 0xb7
)
var machineNames = scalar.UToScalar{
0x00: {Description: "No specific instruction set"},
0x01: {Sym: "we_32100", Description: "AT&T WE 32100"},
0x02: {Sym: "sparc", Description: "SPARC"},
0x03: {Sym: "x86", Description: "x86"},
0x04: {Sym: "m68k", Description: "Motorola 68000 (M68k)"},
0x05: {Sym: "m88k", Description: "Motorola 88000 (M88k)"},
0x06: {Sym: "intel_mcu", Description: "Intel MCU"},
0x07: {Sym: "intel_80860", Description: "Intel 80860"},
0x08: {Sym: "mips", Description: "MIPS"},
0x09: {Sym: "s370", Description: "IBM_System/370"},
0x0a: {Sym: "mips_rs3000le", Description: "MIPS RS3000 Little-endian"},
0x0e: {Sym: "pa_risc", Description: "Hewlett-Packard PA-RISC"},
0x0f: {Description: "Reserved for future use"},
0x13: {Sym: "80960", Description: "Intel 80960"},
0x14: {Sym: "powerpc", Description: "PowerPC"},
0x15: {Sym: "powerpc64", Description: "PowerPC (64-bit)"},
0x16: {Sym: "s390", Description: "S390, including S390x"},
0x17: {Sym: "ibm_spu_spc", Description: "IBM SPU/SPC"},
0x24: {Sym: "nec_v800", Description: "NEC V800"},
0x25: {Sym: "fr20", Description: "Fujitsu FR20"},
0x26: {Sym: "trw_rh_32", Description: "TRW RH-32"},
0x27: {Sym: "motorola_rce", Description: "Motorola RCE"},
0x28: {Sym: "arm", Description: "ARM (up to ARMv7/Aarch32)"},
0x29: {Sym: "alpha", Description: "Digital Alpha"},
0x2a: {Sym: "superh", Description: "SuperH"},
0x2b: {Sym: "sparc_v9", Description: "SPARC Version 9"},
0x2c: {Sym: "siemens_tricore", Description: "Siemens TriCore embedded processor"},
0x2d: {Sym: "argonaut_risc", Description: "Argonaut RISC Core"},
0x2e: {Sym: "h8_300", Description: "Hitachi H8/300"},
0x2f: {Sym: "h8_300h", Description: "Hitachi H8/300H"},
0x30: {Sym: "h8s", Description: "Hitachi H8S"},
0x31: {Sym: "h8/500", Description: "Hitachi H8/500"},
0x32: {Sym: "ia_64", Description: "IA-64"},
0x33: {Sym: "mips_x", Description: "Stanford MIPS-X"},
0x34: {Sym: "coldfire", Description: "Motorola ColdFire"},
0x35: {Sym: "m68hc12", Description: "Motorola M68HC12"},
0x36: {Sym: "fujitsu_mma", Description: "Fujitsu MMA Multimedia Accelerator"},
0x37: {Sym: "siemens_pcp", Description: "Siemens PCP"},
0x38: {Sym: "sony_ncpu_risc", Description: "Sony nCPU embedded RISC processor"},
0x39: {Sym: "denso_ndr1", Description: "Denso NDR1 microprocessor"},
0x3a: {Sym: "motorola_star", Description: "Motorola Star*Core processor"},
0x3b: {Sym: "toyota_me16", Description: "Toyota ME16 processor"},
0x3c: {Sym: "st100", Description: "STMicroelectronics ST100 processor"},
0x3d: {Sym: "tinyj", Description: "Advanced Logic Corp. TinyJ embedded processor family"},
EM_X86_64: {Sym: "x86_64", Description: "AMD x86-64"},
0x8c: {Sym: "tms320C6000", Description: "TMS320C6000 Family"},
EM_ARM64: {Sym: "arm64", Description: "ARM 64-bits (ARMv8/Aarch64)"},
0xf3: {Sym: "risc_v", Description: "RISC-V"},
0xf7: {Sym: "bpf", Description: "Berkeley Packet Filter"},
0x101: {Sym: "wdc_65C816", Description: "WDC 65C816"},
}
var phTypeNames = scalar.URangeToScalar{
{Range: [2]uint64{0x00000000, 0x00000000}, S: scalar.S{Sym: "null", Description: "Unused element"}},
{Range: [2]uint64{0x00000001, 0x00000001}, S: scalar.S{Sym: "load", Description: "Loadable segment"}},
{Range: [2]uint64{0x00000002, 0x00000002}, S: scalar.S{Sym: "dynamic", Description: "Dynamic linking information"}},
{Range: [2]uint64{0x00000003, 0x00000003}, S: scalar.S{Sym: "interp", Description: "Interpreter to invoke"}},
{Range: [2]uint64{0x00000004, 0x00000004}, S: scalar.S{Sym: "note", Description: "Auxiliary information"}},
{Range: [2]uint64{0x00000005, 0x00000005}, S: scalar.S{Sym: "shlib", Description: "Reserved but has unspecified"}},
{Range: [2]uint64{0x00000006, 0x00000006}, S: scalar.S{Sym: "phdr", Description: "Program header location and size"}},
{Range: [2]uint64{0x00000007, 0x00000007}, S: scalar.S{Sym: "tls", Description: "Thread-Local Storage template"}},
{Range: [2]uint64{0x6474e550, 0x6474e550}, S: scalar.S{Sym: "gnu_eh_frame", Description: "GNU frame unwind information"}},
{Range: [2]uint64{0x6474e551, 0x6474e551}, S: scalar.S{Sym: "gnu_stack", Description: "GNU stack permission"}},
{Range: [2]uint64{0x6474e552, 0x6474e552}, S: scalar.S{Sym: "gnu_relro", Description: "GNU read-only after relocation"}},
{Range: [2]uint64{0x60000000, 0x6fffffff}, S: scalar.S{Sym: "os", Description: "Operating system-specific"}},
{Range: [2]uint64{0x70000000, 0x7fffffff}, S: scalar.S{Sym: "proc", Description: "Processor-specific"}},
}
const (
SHT_NULL = 0x0
SHT_PROGBITS = 0x1
SHT_SYMTAB = 0x2
SHT_STRTAB = 0x3
SHT_RELA = 0x4
SHT_HASH = 0x5
SHT_DYNAMIC = 0x6
SHT_NOTE = 0x7
SHT_NOBITS = 0x8
SHT_REL = 0x9
SHT_SHLIB = 0x0a
SHT_DYNSYM = 0x0b
SHT_INIT_ARRAY = 0x0e
SHT_FINI_ARRAY = 0x0f
SHT_PREINIT_ARRAY = 0x10
SHT_GROUP = 0x11
SHT_SYMTAB_SHNDX = 0x12
SHT_GNU_HASH = 0x6ffffff6
)
var sectionHeaderTypeMap = scalar.UToScalar{
SHT_NULL: {Sym: "null", Description: "Header inactive"},
SHT_PROGBITS: {Sym: "progbits", Description: "Information defined by the program"},
SHT_SYMTAB: {Sym: "symtab", Description: "Symbol table"},
SHT_STRTAB: {Sym: "strtab", Description: "String table"},
SHT_RELA: {Sym: "rela", Description: "Relocation entries with explicit addends"},
SHT_HASH: {Sym: "hash", Description: "Symbol hash table"},
SHT_DYNAMIC: {Sym: "dynamic", Description: "Information for dynamic linking"},
SHT_NOTE: {Sym: "note", Description: "Information that marks the file in some way"},
SHT_NOBITS: {Sym: "nobits", Description: "No space in the file"},
SHT_REL: {Sym: "rel", Description: "Relocation entries without explicit addends"},
SHT_SHLIB: {Sym: "shlib", Description: "Reserved but has unspecified semantics"},
SHT_DYNSYM: {Sym: "dynsym", Description: "Dynamic linking symbol table"},
SHT_INIT_ARRAY: {Sym: "init_array", Description: "Initialization functions"},
SHT_FINI_ARRAY: {Sym: "fini_array", Description: "Termination functions"},
SHT_PREINIT_ARRAY: {Sym: "preinit_array", Description: "Pre initialization functions"},
SHT_GROUP: {Sym: "group", Description: "Section group"},
SHT_SYMTAB_SHNDX: {Sym: "symtab_shndx", Description: ""},
SHT_GNU_HASH: {Sym: "gnu_hash", Description: "GNU symbol hash table"},
}
const (
STRTAB_DYNSTR = ".dynstr"
STRTAB_SHSTRTAB = ".shstrtab"
STRTAB_STRTAB = ".strtab"
)
const (
DT_NULL = 0
DT_NEEDED = 1
DT_PLTRELSZ = 2
DT_PLTGOT = 3
DT_HASH = 4
DT_STRTAB = 5
DT_SYMTAB = 6
DT_RELA = 7
DT_RELASZ = 8
DT_RELAENT = 9
DT_STRSZ = 10
DT_SYMENT = 11
DT_INIT = 12
DT_FINI = 13
DT_SONAME = 14
DT_RPATH = 15
DT_SYMBOLIC = 16
DT_REL = 17
DT_RELSZ = 18
DT_RELENT = 19
DT_PLTREL = 20
DT_DEBUG = 21
DT_TEXTREL = 22
DT_JMPREL = 23
DT_BIND_NOW = 24
DT_INIT_ARRAY = 25
DT_FINI_ARRAY = 26
DT_INIT_ARRAYSZ = 27
DT_FINI_ARRAYSZ = 28
DT_RUNPATH = 29
DT_FLAGS = 30 // TODO: flag map
DT_ENCODING = 32 // or DT_PREINIT_ARRAY ?
DT_PREINIT_ARRAYSZ = 33
DT_LOOS = 0x6000000D
DT_HIOS = 0x6ffff000
DT_LOPROC = 0x70000000
DT_HIPROC = 0x7fffffff
)
const (
dUnIgnored = iota
dUnVal
dUnPtr
dUnUnspecified
)
type dtEntry struct {
r [2]uint64
dUn int
s scalar.S
}
type dynamicTableEntries []dtEntry
func (d dynamicTableEntries) lookup(u uint64) (dtEntry, bool) {
for _, de := range d {
if de.r[0] >= u && de.r[1] <= u {
return de, true
}
}
return dtEntry{}, false
}
func (d dynamicTableEntries) MapScalar(s scalar.S) (scalar.S, error) {
u := s.ActualU()
if de, ok := d.lookup(u); ok {
s = de.s
s.Actual = u
}
return s, nil
}
var dynamicTableMap = dynamicTableEntries{
{r: [2]uint64{DT_NULL, DT_NULL}, dUn: dUnIgnored, s: scalar.S{Sym: "null", Description: "Marks end of dynamic section"}},
{r: [2]uint64{DT_NEEDED, DT_NEEDED}, dUn: dUnVal, s: scalar.S{Sym: "needed", Description: "String table offset to name of a needed library"}},
{r: [2]uint64{DT_PLTRELSZ, DT_PLTRELSZ}, dUn: dUnVal, s: scalar.S{Sym: "pltrelsz", Description: "Size in bytes of PLT relocation entries"}},
{r: [2]uint64{DT_PLTGOT, DT_PLTGOT}, dUn: dUnPtr, s: scalar.S{Sym: "pltgot", Description: "Address of PLT and/or GOT"}},
{r: [2]uint64{DT_HASH, DT_HASH}, dUn: dUnPtr, s: scalar.S{Sym: "hash", Description: "Address of symbol hash table"}},
{r: [2]uint64{DT_STRTAB, DT_STRTAB}, dUn: dUnPtr, s: scalar.S{Sym: "strtab", Description: "Address of string table"}},
{r: [2]uint64{DT_SYMTAB, DT_SYMTAB}, dUn: dUnPtr, s: scalar.S{Sym: "symtab", Description: "Address of symbol table"}},
{r: [2]uint64{DT_RELA, DT_RELA}, dUn: dUnPtr, s: scalar.S{Sym: "rela", Description: "Address of Rela relocation table"}},
{r: [2]uint64{DT_RELASZ, DT_RELASZ}, dUn: dUnVal, s: scalar.S{Sym: "relasz", Description: "Size in bytes of the Rela relocation table"}},
{r: [2]uint64{DT_RELAENT, DT_RELAENT}, dUn: dUnVal, s: scalar.S{Sym: "relaent", Description: "Size in bytes of a Rela relocation table entry"}},
{r: [2]uint64{DT_STRSZ, DT_STRSZ}, dUn: dUnVal, s: scalar.S{Sym: "strsz", Description: "Size in bytes of string table"}},
{r: [2]uint64{DT_SYMENT, DT_SYMENT}, dUn: dUnVal, s: scalar.S{Sym: "syment", Description: "Size in bytes of a symbol table entry"}},
{r: [2]uint64{DT_INIT, DT_INIT}, dUn: dUnPtr, s: scalar.S{Sym: "init", Description: "Address of the initialization function"}},
{r: [2]uint64{DT_FINI, DT_FINI}, dUn: dUnPtr, s: scalar.S{Sym: "fini", Description: "Address of the termination function"}},
{r: [2]uint64{DT_SONAME, DT_SONAME}, dUn: dUnVal, s: scalar.S{Sym: "soname", Description: "String table offset to name of shared object"}},
{r: [2]uint64{DT_RPATH, DT_RPATH}, dUn: dUnVal, s: scalar.S{Sym: "rpath", Description: "String table offset to library search path (deprecated)"}},
{r: [2]uint64{DT_SYMBOLIC, DT_SYMBOLIC}, dUn: dUnIgnored, s: scalar.S{Sym: "symbolic", Description: "Alert linker to search this shared object before the executable for symbols DT_REL Address of Rel relocation table"}},
{r: [2]uint64{DT_REL, DT_REL}, dUn: dUnPtr, s: scalar.S{Sym: "rel", Description: ""}},
{r: [2]uint64{DT_RELSZ, DT_RELSZ}, dUn: dUnVal, s: scalar.S{Sym: "relsz", Description: "Size in bytes of Rel relocation table"}},
{r: [2]uint64{DT_RELENT, DT_RELENT}, dUn: dUnVal, s: scalar.S{Sym: "relent", Description: "Size in bytes of a Rel table entry"}},
{r: [2]uint64{DT_PLTREL, DT_PLTREL}, dUn: dUnVal, s: scalar.S{Sym: "pltrel", Description: "Type of relocation entry to which the PLT refers (Rela or Rel)"}},
{r: [2]uint64{DT_DEBUG, DT_DEBUG}, dUn: dUnPtr, s: scalar.S{Sym: "debug", Description: "Undefined use for debugging"}},
{r: [2]uint64{DT_TEXTREL, DT_TEXTREL}, dUn: dUnIgnored, s: scalar.S{Sym: "textrel", Description: "Absence of this entry indicates that no relocation entries should apply to a nonwritable segment"}},
{r: [2]uint64{DT_JMPREL, DT_JMPREL}, dUn: dUnPtr, s: scalar.S{Sym: "jmprel", Description: "Address of relocation entries associated solely with the PLT"}},
{r: [2]uint64{DT_BIND_NOW, DT_BIND_NOW}, dUn: dUnIgnored, s: scalar.S{Sym: "bind_now", Description: "Instruct dynamic linker to process all relocations before transferring control to the executable"}},
{r: [2]uint64{DT_INIT_ARRAY, DT_INIT_ARRAY}, dUn: dUnPtr, s: scalar.S{Sym: "init_array", Description: "Address of the array of pointers to initialization functions"}},
{r: [2]uint64{DT_FINI_ARRAY, DT_FINI_ARRAY}, dUn: dUnPtr, s: scalar.S{Sym: "fini_array", Description: "Address of the array of pointers to termination functions"}},
{r: [2]uint64{DT_INIT_ARRAYSZ, DT_INIT_ARRAYSZ}, dUn: dUnVal, s: scalar.S{Sym: "init_arraysz", Description: "Size in bytes of the array of initialization functions"}},
{r: [2]uint64{DT_FINI_ARRAYSZ, DT_FINI_ARRAYSZ}, dUn: dUnVal, s: scalar.S{Sym: "fini_arraysz", Description: "Size in bytes of the array of termination functions "}},
{r: [2]uint64{DT_RUNPATH, DT_RUNPATH}, dUn: dUnVal, s: scalar.S{Sym: "runpath", Description: "String table offset to library search path"}},
{r: [2]uint64{DT_FLAGS, DT_FLAGS}, dUn: dUnVal, s: scalar.S{Sym: "flags", Description: "Flag values specific to the object being loaded"}}, // TODO: flag ma}},
{r: [2]uint64{DT_ENCODING, DT_ENCODING}, dUn: dUnUnspecified, s: scalar.S{Sym: "encoding", Description: ""}}, // or DT_PREINIT_ARRAY }},
{r: [2]uint64{DT_PREINIT_ARRAYSZ, DT_PREINIT_ARRAYSZ}, dUn: dUnVal, s: scalar.S{Sym: "preinit_arraysz", Description: "Address of the array of pointers to pre-initialization functions"}},
{r: [2]uint64{DT_LOOS, DT_HIOS}, dUn: dUnUnspecified, s: scalar.S{Sym: "lo", Description: "Operating system-specific semantics"}},
{r: [2]uint64{DT_LOPROC, DT_HIPROC}, dUn: dUnUnspecified, s: scalar.S{Sym: "proc", Description: "Processor-specific semantics"}},
}
var symbolTableBindingMap = scalar.UToSymStr{
0: "local",
1: "global",
2: "weak",
10: "loos",
12: "hios",
13: "proc",
14: "proc",
15: "proc",
}
var symbolTableTypeMap = scalar.UToSymStr{
0: "notype",
1: "object",
2: "func",
3: "section",
4: "file",
5: "common",
6: "tls",
10: "loos",
12: "hios",
13: "proc",
14: "proc",
15: "proc",
}
var symbolTableVisibilityMap = scalar.UToSymStr{
0: "default",
1: "internal",
2: "hidden",
3: "protected",
}
func strIndexNull(idx int, s string) string {
if idx > len(s) {
return ""
}
i := strings.IndexByte(s[idx:], 0)
if i == -1 {
return s
}
return s[idx : idx+i]
}
type strTable string
func (m strTable) MapScalar(s scalar.S) (scalar.S, error) {
s.Sym = strIndexNull(int(s.ActualU()), string(m))
return s, nil
}
func elfDecodeSymbolHashTable(d *decode.D) {
nBucket := d.FieldU32("nbucket")
nChain := d.FieldU32("nchain")
repeatFn := func(r int, fn func(d *decode.D)) func(d *decode.D) {
return func(d *decode.D) {
for i := 0; i < r; i++ {
fn(d)
}
}
}
d.FieldArray("buckets", repeatFn(int(nBucket), func(d *decode.D) { d.FieldU32("bucket") }))
d.FieldArray("chains", repeatFn(int(nChain), func(d *decode.D) { d.FieldU32("chain") }))
}
func elfDecodeSymbolTable(d *decode.D, ec elfContext, nEntries int, strTab string) {
for i := 0; i < nEntries; i++ {
d.FieldStruct("symbol", func(d *decode.D) {
switch ec.archBits {
case 32:
d.FieldU32("name", strTable(strTab))
d.FieldU32("value")
d.FieldU32("size")
d.FieldU4("bind", symbolTableBindingMap)
d.FieldU4("type", symbolTableTypeMap)
d.FieldU6("other_unused")
d.FieldU2("visibility", symbolTableVisibilityMap)
d.FieldU16("shndx")
case 64:
d.FieldU32("name", strTable(strTab))
d.FieldU4("bind", symbolTableBindingMap)
d.FieldU4("type", symbolTableTypeMap)
d.FieldU6("other_unused")
d.FieldU2("visibility", symbolTableVisibilityMap)
d.FieldU16("shndx")
d.FieldU64("value")
d.FieldU64("size")
}
})
}
}
func elfDecodeGNUHash(d *decode.D, ec elfContext, size int64, strTab string) {
d.FramedFn(size, func(d *decode.D) {
nBuckets := d.FieldU32("nbuckets")
d.FieldU32("symndx")
maskwords := d.FieldU32("maskwords")
d.FieldU32("shift2")
repeatFn := func(r int, fn func(d *decode.D)) func(d *decode.D) {
return func(d *decode.D) {
for i := 0; i < r; i++ {
fn(d)
}
}
}
// TODO: possible to map to symbols?
_ = strTab
d.FieldArray("bloom_filter", repeatFn(int(maskwords), func(d *decode.D) { d.FieldU("maskword", ec.archBits) }))
d.FieldArray("buckets", repeatFn(int(nBuckets), func(d *decode.D) { d.FieldU32("bucket") }))
d.FieldArray("values", func(d *decode.D) {
for !d.End() {
d.FieldU32("value")
}
})
})
}
type dynamicContext struct {
entries int
strTabPtr int64
strSzVal int64
strTab string
symEnt int64
}
func elfReadDynamicTags(d *decode.D, ec *elfContext) dynamicContext {
var strTabPtr int64
var strSzVal int64
var symEnt int64
var entries int
seenNull := false
for !seenNull {
entries++
tag := d.U(ec.archBits)
valPtr := d.U(ec.archBits)
switch tag {
case DT_STRTAB:
strTabPtr = int64(valPtr) * 8
case DT_STRSZ:
strSzVal = int64(valPtr) * 8
case DT_SYMENT:
symEnt = int64(valPtr) * 8
case DT_NULL:
seenNull = true
}
}
return dynamicContext{
entries: entries,
strTabPtr: strTabPtr,
strSzVal: strSzVal,
symEnt: symEnt,
}
}
type symbol struct {
name uint64
value uint64
}
func elfReadSymbolTable(d *decode.D, ec *elfContext, sh sectionHeader) []symbol {
var ss []symbol
for i := 0; i < int(sh.size/sh.entSize); i++ {
var name uint64
var value uint64
switch ec.archBits {
case 32:
name = d.U32() // name
value = d.U32() // value
d.U32() // size
d.U4() // bind
d.U4() // type
d.U6() // other_unused
d.U2() // visibility
d.U16() // shndx
case 64:
name = d.U32() // name
d.U4() // bind
d.U4() // type
d.U6() // other_unused
d.U2() // visibility
d.U16() // shndx
value = d.U64() // value
d.U64() // size
}
ss = append(ss, symbol{name: name, value: value})
}
return ss
}
type sectionHeader struct {
addr int64
offset int64
size int64
entSize int64
name int
typ int
dc dynamicContext // if SHT_DYNAMIC
symbols []symbol
}
const maxStrTabSize = 100_000_000
func readStrTab(d *decode.D, firstBit int64, nBytes int64) string {
if nBytes > maxStrTabSize {
d.Errorf("string table too large %d > %d", nBytes, maxStrTabSize)
}
return string(d.BytesRange(firstBit, int(nBytes)))
}
func elfReadSectionHeaders(d *decode.D, ec *elfContext) {
for i := 0; i < ec.shNum; i++ {
d.SeekAbs(ec.shOff + int64(i)*ec.shEntSize)
var sh sectionHeader
switch ec.archBits {
case 32:
sh.name = int(d.U32())
sh.typ = int(d.U32())
d.U32() // flags
sh.addr = int64(d.U32() * 8) // addr
sh.offset = int64(d.U32()) * 8
sh.size = int64(d.U32()) * 8
d.U32() // link
d.U32() // info
d.U32() // addralign
sh.entSize = int64(d.U32()) * 8
case 64:
sh.name = int(d.U32())
sh.typ = int(d.U32())
d.U64() // addr
sh.addr = int64(d.U64() * 8) // flags
sh.offset = int64(d.U64()) * 8
sh.size = int64(d.U64()) * 8
d.U32() // link
d.U32() // info
d.U64() // addralign
sh.entSize = int64(d.U64()) * 8
default:
panic("unreachable")
}
switch sh.typ {
case SHT_DYNAMIC:
d.SeekAbs(sh.offset)
sh.dc = elfReadDynamicTags(d, ec)
case SHT_SYMTAB:
d.SeekAbs(sh.offset)
sh.symbols = elfReadSymbolTable(d, ec, sh)
}
ec.sections = append(ec.sections, sh)
}
// for dynamic linking sections find offset to string table by looking up
// section by address using string stable address
for i := range ec.sections {
sh := &ec.sections[i]
if sh.typ != SHT_DYNAMIC {
continue
}
if i, ok := ec.sectionIndexByAddr(sh.dc.strTabPtr); ok {
strTabSh := ec.sections[i]
sh.dc.strTab = readStrTab(d, strTabSh.offset, sh.dc.strSzVal/8)
}
}
ec.strTabMap = map[string]string{}
var shStrTab string
if ec.shStrNdx >= len(ec.sections) {
d.Fatalf("can't find shStrNdx %d", ec.shStrNdx)
}
sh := ec.sections[ec.shStrNdx]
shStrTab = readStrTab(d, sh.offset, sh.size/8)
for _, sh := range ec.sections {
if sh.typ != SHT_STRTAB {
continue
}
ec.strTabMap[strIndexNull(sh.name, shStrTab)] = readStrTab(d, sh.offset, sh.size/8)
}
}
type elfContext struct {
archBits int
machine int
endian decode.Endian
phOff int64
phNum int
phSize int64
shOff int64
shNum int
shEntSize int64
shStrNdx int
sections []sectionHeader
strTabMap map[string]string
}
func (ec *elfContext) sectionIndexByAddr(addr int64) (int, bool) {
for i, s := range ec.sections {
if s.addr == addr {
return i, true
}
}
return 0, false
}
func elfDecodeHeader(d *decode.D, ec *elfContext) {
var class uint64
var archBits int
var endian uint64
d.FieldStruct("ident", func(d *decode.D) {
d.FieldRawLen("magic", 4*8, d.AssertBitBuf([]byte("\x7fELF")))
class = d.FieldU8("class", classBits)
endian = d.FieldU8("data", endianNames)
d.FieldU8("version")
d.FieldU8("os_abi", osABINames)
d.FieldU8("abi_version")
d.FieldRawLen("pad", 7*8, d.BitBufIsZero())
})
switch class {
case CLASS_32:
archBits = 32
case CLASS_64:
archBits = 64
default:
d.Fatalf("unknown class %d", class)
}
switch endian {
case LITTLE_ENDIAN:
d.Endian = decode.LittleEndian
case BIG_ENDIAN:
d.Endian = decode.BigEndian
default:
d.Fatalf("unknown endian %d", endian)
}
d.FieldU16("type", typeNames, scalar.ActualHex)
machine := d.FieldU16("machine", machineNames, scalar.ActualHex)
d.FieldU32("version")
d.FieldU("entry", archBits)
phOff := d.FieldU("phoff", archBits)
shOff := d.FieldU("shoff", archBits)
d.FieldU32("flags")
d.FieldU16("ehsize")
phSize := d.FieldU16("phentsize")
phNum := d.FieldU16("phnum")
shEntSize := d.FieldU16("shentsize")
shNum := d.FieldU16("shnum")
shStrNdx := d.FieldU16("shstrndx")
ec.archBits = archBits
ec.endian = d.Endian
ec.machine = int(machine)
ec.phOff = int64(phOff) * 8
ec.phNum = int(phNum)
ec.phSize = int64(phSize) * 8
ec.shOff = int64(shOff) * 8
ec.shNum = int(shNum)
ec.shEntSize = int64(shEntSize) * 8
ec.shStrNdx = int(shStrNdx)
}
func elfDecodeProgramHeader(d *decode.D, ec elfContext) {
pFlags := func(d *decode.D) {
d.FieldStruct("flags", func(d *decode.D) {
if d.Endian == decode.LittleEndian {
d.FieldU5("unused0")
d.FieldBool("r")
d.FieldBool("w")
d.FieldBool("x")
d.FieldU24("unused1")
} else {
d.FieldU29("unused0")
d.FieldBool("r")
d.FieldBool("w")
d.FieldBool("x")
}
})
}
var offset uint64
var size uint64
switch ec.archBits {
case 32:
d.FieldU32("type", phTypeNames)
offset = d.FieldU("offset", ec.archBits, scalar.ActualHex)
d.FieldU("vaddr", ec.archBits, scalar.ActualHex)
d.FieldU("paddr", ec.archBits, scalar.ActualHex)
size = d.FieldU32("filesz")
d.FieldU32("memsz")
pFlags(d)
d.FieldU32("align")
case 64:
d.FieldU32("type", phTypeNames)
pFlags(d)
offset = d.FieldU("offset", ec.archBits, scalar.ActualHex)
d.FieldU("vaddr", ec.archBits, scalar.ActualHex)
d.FieldU("paddr", ec.archBits, scalar.ActualHex)
size = d.FieldU64("filesz")
d.FieldU64("memsz")
d.FieldU64("align")
}
d.RangeFn(int64(offset*8), int64(size*8), func(d *decode.D) {
d.FieldRawLen("data", d.BitsLeft())
})
}
func elfDecodeProgramHeaders(d *decode.D, ec elfContext) {
for i := 0; i < ec.phNum; i++ {
d.FieldStruct("program_header", func(d *decode.D) {
d.SeekAbs(ec.phOff + int64(i)*ec.phSize)
elfDecodeProgramHeader(d, ec)
})
}
}
func elfDecodeDynamicTag(d *decode.D, ec elfContext, dc dynamicContext) {
dtTag := d.FieldU("tag", ec.archBits, dynamicTableMap)
name := "unspecified"
dfMapper := scalar.ActualHex
if de, ok := dynamicTableMap.lookup(dtTag); ok {
switch de.dUn {
case dUnIgnored:
name = "ignored"
case dUnVal:
name = "val"
dfMapper = scalar.ActualDec
case dUnPtr:
name = "ptr"
}
}
switch dtTag {
case DT_NEEDED:
d.FieldU(name, ec.archBits, dfMapper, strTable(dc.strTab))
case DT_HASH:
v := d.FieldU(name, ec.archBits, dfMapper)
if i, ok := ec.sectionIndexByAddr(int64(v) * 8); ok {
d.FieldValueU("section_index", uint64(i))
}
case DT_SYMTAB,
DT_STRTAB,
DT_PLTGOT,
DT_JMPREL,
DT_INIT,
DT_FINI:
v := d.FieldU(name, ec.archBits, dfMapper)
if i, ok := ec.sectionIndexByAddr(int64(v) * 8); ok {
d.FieldValueU("section_index", uint64(i))
}
default:
d.FieldU(name, ec.archBits, dfMapper)
}
}
func elfDecodeDynamicTags(d *decode.D, ec elfContext, dc dynamicContext) {
for i := 0; i < dc.entries; i++ {
d.FieldStruct("dynamic_tags", func(d *decode.D) {
elfDecodeDynamicTag(d, ec, dc)
})
}
}
func elfDecodeSectionHeader(d *decode.D, ec elfContext, sh sectionHeader) {
shFlags := func(d *decode.D, archBits int) {
d.FieldStruct("flags", func(d *decode.D) {
if d.Endian == decode.LittleEndian {
d.FieldBool("link_order")
d.FieldBool("info_link")
d.FieldBool("strings")
d.FieldBool("merge")
d.FieldU1("unused0")
d.FieldBool("execinstr")
d.FieldBool("alloc")
d.FieldBool("write")
d.FieldBool("tls")
d.FieldBool("group")
d.FieldBool("os_nonconforming")
d.FieldU9("unused1")
d.FieldU8("os_specific")
d.FieldU4("processor_specific")
if archBits == 64 {
d.FieldU32("unused2")
}
} else {
// TODO: add.FieldUnused that is per decoder?
if archBits == 64 {
d.FieldU32("unused0")
}
d.FieldU4("processor_specific")
d.FieldU8("os_specific")
d.FieldU9("unused1")
d.FieldBool("tls")
d.FieldBool("group")
d.FieldBool("os_nonconforming")
d.FieldBool("link_order")
d.FieldBool("info_link")
d.FieldBool("strings")
d.FieldBool("merge")
d.FieldU1("unused2")
d.FieldBool("execinstr")
d.FieldBool("alloc")
d.FieldBool("write")
}
})
}
var offset int64
var size int64
var entSize int64
var typ uint64
switch ec.archBits {
case 32:
d.FieldU32("name", strTable(ec.strTabMap[STRTAB_SHSTRTAB]))
typ = d.FieldU32("type", sectionHeaderTypeMap, scalar.ActualHex)
shFlags(d, ec.archBits)
d.FieldU("addr", ec.archBits, scalar.ActualHex)
offset = int64(d.FieldU("offset", ec.archBits)) * 8
size = int64(d.FieldU32("size", scalar.ActualHex) * 8)
d.FieldU32("link")
d.FieldU32("info")
d.FieldU32("addralign")
entSize = int64(d.FieldU32("entsize") * 8)
case 64:
d.FieldU32("name", strTable(ec.strTabMap[STRTAB_SHSTRTAB]))
typ = d.FieldU32("type", sectionHeaderTypeMap, scalar.ActualHex)
shFlags(d, ec.archBits)
d.FieldU("addr", ec.archBits, scalar.ActualHex)
offset = int64(d.FieldU("offset", ec.archBits, scalar.ActualHex) * 8)
size = int64(d.FieldU64("size") * 8)
d.FieldU32("link")
d.FieldU32("info")
d.FieldU64("addralign")
entSize = int64(d.FieldU64("entsize") * 8)
}
if typ == SHT_NOBITS {
// section occupies no space in file
return
}
d.SeekAbs(offset)
switch typ {
case SHT_STRTAB:
d.FieldUTF8("string", int(size/8))
case SHT_DYNAMIC:
d.FieldArray("dynamic_tags", func(d *decode.D) {
elfDecodeDynamicTags(d, ec, sh.dc)
})
case SHT_HASH:
d.FieldStruct("symbol_hash_table", elfDecodeSymbolHashTable)
case SHT_SYMTAB:
d.FieldArray("symbol_table", func(d *decode.D) {
elfDecodeSymbolTable(d, ec, int(size/entSize), ec.strTabMap[STRTAB_STRTAB])
})
case SHT_DYNSYM:
d.FieldArray("symbol_table", func(d *decode.D) {
elfDecodeSymbolTable(d, ec, int(size/entSize), ec.strTabMap[STRTAB_DYNSTR])
})
case SHT_PROGBITS:
// TODO: name progbits?
// TODO: decode opcodes
d.FieldRawLen("data", size)
case SHT_GNU_HASH:
d.FieldStruct("gnu_hash", func(d *decode.D) {
elfDecodeGNUHash(d, ec, size, ec.strTabMap[STRTAB_DYNSTR])
})
default:
d.FieldRawLen("data", size)
}
}
func elfDecodeSectionHeaders(d *decode.D, ec elfContext) {
for i := 0; i < ec.shNum; i++ {
d.SeekAbs(ec.shOff + int64(i)*ec.shEntSize)
d.FieldStruct("section_header", func(d *decode.D) {
elfDecodeSectionHeader(d, ec, ec.sections[i])
})
}
}
func elfDecode(d *decode.D, _ any) any {
var ec elfContext
d.FieldStruct("header", func(d *decode.D) { elfDecodeHeader(d, &ec) })
d.Endian = ec.endian
// a first pass to find all sections and string table information etc
elfReadSectionHeaders(d, &ec)
d.FieldArray("program_headers", func(d *decode.D) {
elfDecodeProgramHeaders(d, ec)
})
d.FieldArray("section_headers", func(d *decode.D) {
elfDecodeSectionHeaders(d, ec)
})
return nil
}
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