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elf.go
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//go:build !remote
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package emulation
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import (
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	"debug/elf"
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	"encoding/binary"
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	"fmt"
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	"sync"
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	"github.com/sirupsen/logrus"
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)
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type elfPlatform struct {
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	platform string
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	osabi    []elf.OSABI
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	class    elf.Class
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	data     elf.Data
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	alsoNone bool // also try with data=none,version=0
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	machine  elf.Machine
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	flags    []uint32
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}
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var (
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	// knownELFPlatformHeaders is a mapping from target platform names and
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	// plausible headers for the binaries built for those platforms.  Call
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	// getKnownELFPlatformHeaders() instead of reading this map directly.
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	knownELFPlatformHeaders     = make(map[string][][]byte)
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	knownELFPlatformHeadersOnce sync.Once
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	// knownELFPlatforms is a table of target platforms that we built a
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	// trivial program for, and the other fields are filled in based on
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	// what we got when we ran eu-readelf -h against the results.
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	knownELFPlatforms = []elfPlatform{
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		{
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			platform: "linux/386",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS32,
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			data:     elf.ELFDATA2LSB,
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			alsoNone: true,
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			machine:  elf.EM_386,
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		},
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		{
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			platform: "linux/amd64",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS64,
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			data:     elf.ELFDATA2LSB,
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			alsoNone: true,
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			machine:  elf.EM_X86_64,
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		},
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		{
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			platform: "linux/arm",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS32,
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			data:     elf.ELFDATA2LSB,
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			machine:  elf.EM_ARM,
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		},
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		{
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			platform: "linux/arm64",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS64,
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			data:     elf.ELFDATA2LSB,
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			machine:  elf.EM_AARCH64,
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		},
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		{
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			platform: "linux/arm64be",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS64,
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			data:     elf.ELFDATA2MSB,
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			machine:  elf.EM_AARCH64,
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		},
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		{
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			platform: "linux/loong64",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS64,
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			data:     elf.ELFDATA2LSB,
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			machine:  elf.EM_LOONGARCH,
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		},
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		{
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			platform: "linux/mips",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS32,
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			data:     elf.ELFDATA2MSB,
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			machine:  elf.EM_MIPS,
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			flags:    []uint32{0, 2}, // elf.EF_MIPS_PIC set, or not
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		},
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		{
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			platform: "linux/mipsle",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS32,
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			data:     elf.ELFDATA2LSB,
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			machine:  elf.EM_MIPS_RS3_LE,
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			flags:    []uint32{0, 2}, // elf.EF_MIPS_PIC set, or not
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		},
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		{
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			platform: "linux/mips64",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS64,
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			data:     elf.ELFDATA2MSB,
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			machine:  elf.EM_MIPS,
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			flags:    []uint32{0, 2}, // elf.EF_MIPS_PIC set, or not
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		},
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		{
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			platform: "linux/mips64le",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS64,
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			data:     elf.ELFDATA2LSB,
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			machine:  elf.EM_MIPS_RS3_LE,
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			flags:    []uint32{0, 2}, // elf.EF_MIPS_PIC set, or not
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		},
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		{
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			platform: "linux/ppc",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS32,
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			data:     elf.ELFDATA2MSB,
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			machine:  elf.EM_PPC,
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		},
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		{
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			platform: "linux/ppc64",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS64,
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			data:     elf.ELFDATA2MSB,
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			machine:  elf.EM_PPC64,
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		},
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		{
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			platform: "linux/ppc64le",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS64,
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			data:     elf.ELFDATA2LSB,
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			machine:  elf.EM_PPC64,
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		},
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		{
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			platform: "linux/riscv32",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS32,
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			data:     elf.ELFDATA2LSB,
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			machine:  elf.EM_RISCV,
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		},
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		{
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			platform: "linux/riscv64",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS64,
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			data:     elf.ELFDATA2LSB,
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			machine:  elf.EM_RISCV,
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		},
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		{
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			platform: "linux/s390x",
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			osabi:    []elf.OSABI{elf.ELFOSABI_NONE, elf.ELFOSABI_LINUX},
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			class:    elf.ELFCLASS64,
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			data:     elf.ELFDATA2MSB,
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			machine:  elf.EM_S390,
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		},
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	}
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)
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// header generates an approximation of what the initial N bytes of a binary
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// built for a given target looks like
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func (e *elfPlatform) header() ([][]byte, error) {
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	var headers [][]byte
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	osabi := e.osabi
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	if len(osabi) == 0 {
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		osabi = []elf.OSABI{elf.ELFOSABI_NONE}
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	}
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	for i := range osabi {
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		flags := e.flags
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		if len(flags) == 0 {
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			flags = []uint32{0}
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		}
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		for f := range flags {
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			var endian binary.ByteOrder
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			var entrySize, phoffSize, shoffSize int
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			header := make([]byte, 40)
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			copy(header, elf.ELFMAG)
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			switch e.class {
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			case elf.ELFCLASS32:
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				entrySize, phoffSize, shoffSize = 2, 2, 2
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			case elf.ELFCLASS64:
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				entrySize, phoffSize, shoffSize = 4, 4, 4
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			}
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			switch e.data {
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			case elf.ELFDATA2LSB:
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				endian = binary.LittleEndian
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			case elf.ELFDATA2MSB:
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				endian = binary.BigEndian
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			default:
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				return nil, fmt.Errorf("internal error in entry for %q", e.platform)
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			}
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			header[elf.EI_OSABI] = byte(osabi[i])
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			header[elf.EI_CLASS] = byte(e.class)
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			header[elf.EI_DATA] = byte(e.data)
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			header[elf.EI_VERSION] = byte(elf.EV_CURRENT)
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			header[elf.EI_ABIVERSION] = 0
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			endian.PutUint16(header[16:], uint16(elf.ET_EXEC))
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			endian.PutUint16(header[18:], uint16(e.machine))
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			endian.PutUint32(header[20:], uint32(elf.EV_CURRENT))
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			endian.PutUint32(header[24+entrySize+phoffSize+shoffSize:], flags[f])
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			headers = append(headers, append([]byte{}, header...))
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			if e.alsoNone {
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				header[elf.EI_DATA] = byte(elf.ELFDATANONE)
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				header[elf.EI_VERSION] = byte(elf.EV_NONE)
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				endian.PutUint32(header[20:], uint32(elf.EV_NONE))
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				headers = append(headers, append([]byte{}, header...))
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			}
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		}
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	}
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	return headers, nil
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}
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func getKnownELFPlatformHeaders() map[string][][]byte {
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	knownELFPlatformHeadersOnce.Do(func() {
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		for _, p := range knownELFPlatforms {
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			headerList, err := p.header()
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			if err != nil {
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				logrus.Errorf("generating headers for %q: %v\n", p.platform, err)
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				continue
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			}
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			knownELFPlatformHeaders[p.platform] = headerList
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		}
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	})
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	return knownELFPlatformHeaders
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}
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