15. ELF TOOLS
This sections documents llvm ELF command-line tools along with detailed examples of their usage
llvm-readelf <options> <file>
Inspect ELF files
-h
Display ELF header information:
$ llvm-readelf -h a.out ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) Machine: QUALCOMM DSP6 Processor Version: 0x1 Entry point address: 0x0 Start of program headers: 52 (bytes into file) Start of section headers: 228768 (bytes into file) Flags: 0x68 Size of this header: 52 (bytes) Size of program headers: 32 (bytes) Number of program headers: 4 Size of section headers: 40 (bytes) Number of section headers: 17 Section header string table index: 14-S
List ELF Sections
$ llvm-readelf -S a.out There are 17 section headers, starting at offset 0x37da0: Section Headers: [Nr] Name Type Addr Off Size ES Flg Lk Inf Al [ 0] NULL 00000000 000000 000000 00 0 0 0 [ 1] .start PROGBITS 00000000 001000 0046c8 00 WAX 0 0 64 [ 2] .init PROGBITS 00005000 006000 000064 00 AX 0 0 32 [ 3] .text PROGBITS 00006000 007000 018bcc 00 AX 0 0 4096 [ 4] .fini PROGBITS 0001ebe0 01fbe0 000030 00 AX 0 0 32 ... [11] .sdata PROGBITS 00027000 028000 000170 00 WAp 0 0 4096 [12] .bss NOBITS 00027170 028170 0017d8 00 WA 0 0 8 [13] .comment PROGBITS 00000000 028170 000083 00 MS 0 0 1 [14] .shstrtab STRTAB 00000000 0281f3 000081 00 0 0 1 [15] .symtab SYMTAB 00000000 028274 006d50 10 16 530 4 [16] .strtab STRTAB 00000000 02efc4 008dbd 00 0 0 1-l
List ELF segments:
$ llvm-readelf -l a.out Elf file type is EXEC (Executable file) Entry point 0x0 There are 4 program headers, starting at offset 52 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x001000 0x00000000 0x00000000 0x046c8 0x046c8 RWE 0x1000 LOAD 0x006000 0x00005000 0x00005000 0x1f658 0x1f658 R E 0x1000 LOAD 0x026000 0x00025000 0x00025000 0x02170 0x03948 RW 0x1000 GNU_RELRO 0x026000 0x00025000 0x00025000 0x00044 0x00044 RW 0x4 Section to Segment mapping: Segment Sections... 00 .start 01 .init .text .fini .rodata .eh_frame .gcc_except_table 02 .ctors .dtors .data .sdata .bss 03 .ctors .dtors-s
Display the symbol table
$ llvm-readelf -s hello.o Symbol table '.symtab' contains 324 entries: Num: Value Size Type Bind Vis Ndx Name 0: 00000000 0 NOTYPE LOCAL DEFAULT UND 1: 00000000 0 FILE LOCAL DEFAULT ABS hello.cc 2: 00000090 0 NOTYPE LOCAL DEFAULT 7 GCC_except_table10 3: 00000230 0 NOTYPE LOCAL DEFAULT 7 GCC_except_table100 4: 00000240 0 NOTYPE LOCAL DEFAULT 7 GCC_except_table121 5: 00000268 0 NOTYPE LOCAL DEFAULT 7 GCC_except_table128 ...-r = –relocations
Display relocation entries
$ cat 1.c int foo() { printf("hello world\n"); return 0; } $ clang -c 1.c $ llvm-readelf -r 1.o Relocation section '.rela.text' at offset 0x110 contains 3 entries: Offset Info Type Sym. Value Symbol's Name + Addend 00000004 00000211 R_HEX_32_6_X 00000000 .rodata.str1.1 + 0 00000008 00000217 R_HEX_16_X 00000000 .rodata.str1.1 + 0 0000000c 00000401 R_HEX_B22_PCREL 00000000 printf–string-dump <section>
Treat the contents of a section as a string and print it
$cat 1.c int foo() { printf("hello world\n"); return 0; } $clang 1.c -c $llvm-readelf -S 1.o There are 9 section headers, starting at offset 0x194: Section Headers: [Nr] Name Type Address Off Size ES Flg Lk Inf Al [ 0] NULL 00000000 000000 000000 00 0 0 0 [ 1] .strtab STRTAB 00000000 000131 000061 00 0 0 1 [ 2] .text PROGBITS 00000000 000040 000018 00 AX 0 0 16 [ 3] .rela.text RELA 00000000 00010c 000024 0c 8 2 4 [ 4] .rodata.str1.1 PROGBITS 00000000 000058 00000d 01 AMS 0 0 1 ... $llvm-readelf --string-dump .rodata.str1.1 1.o String dump of section '.rodata.str1.1': [ 0] hello world.–hex-dump <section>
Print the contents of a section as hex
$cat 1.c void foo() {printf("hello world\n")} $clang 1.c -c $llvm-readelf -S 1.o There are 9 section headers, starting at offset 0x194: Section Headers: [Nr] Name Type Address Off Size ES Flg Lk Inf Al [ 0] NULL 00000000 000000 000000 00 0 0 0 [ 1] .strtab STRTAB 00000000 000131 000061 00 0 0 1 [ 2] .text PROGBITS 00000000 000040 000018 00 AX 0 0 16 [ 3] .rela.text RELA 00000000 00010c 000024 0c 8 2 4 [ 4] .rodata.str1.1 PROGBITS 00000000 000058 00000d 01 AMS 0 0 1 ... $llvm-readelf --hex-dump .rodata.str1.1 1.o Hex dump of section '.rodata.str1.1': 0x00000000 68656c6c 6f20776f 726c640a 00 hello world..
llvm-objdump <options> <file>
Disassembler
-d
Show assembler contents of executable sections:
$ llvm-objdump -d a.out a.out: file format ELF32-hexagon Disassembly of section .start: 0000000000000000 start: 0: 4c c0 00 58 5800c04c { jump 0x98 } 4: 3e c0 00 58 5800c03e { jump 0x80 } 8: 42 c0 00 58 5800c042 { jump 0x8c } ...
-r
Display relocation entries involved during linking:
$ llvm-objdump -d -r hello.o hello.o: file format ELF32-hexagon Disassembly of section .text: 0000000000000000 __cxx_global_var_init: 0: 01 c0 9d a0 a09dc001 { allocframe(#8) } 4: 00 40 00 00 00004000 { immext(#0) 00000004: R_HEX_32_6_X .bss 8: 02 c0 00 78 7800c002 r2 = ##0 } 00000008: R_HEX_16_X .bss c: 00 c0 62 70 7062c000 { r0 = r2 } 10: ff e2 9e a7 a79ee2ff { memw(r30+#-4) = r2 } 14: 00 c0 00 5a 5a00c000 { call 0x14 } 00000014: R_HEX_B22_PCREL _ZNSt8ios_base4InitC1Ev ...
llvm-nm <options> <file>
Lists symbols in a file
no args
list regular symbols
$cat 1.c int bar() { return 10; } int foo() { return 1 + bar(); } $clang -c 1.c $llvm-nm 1.o 00000000 T bar 0000000c T foo-D = -dynamic
List dynamic symbols
$cat 1.c int bar() { return 10; } int foo() { return 1 + bar(); } $clang 1.c -o lib.so -fPIC -shared $llvm-nm -D lib.so 000003a0 T _fini 00000240 T _init 00000370 T bar 0000037c T foo-C
List symbols with demangling
llvm-objcopy <options> <input file> <output file>
Copy and translate binary files
no args <input file> <output file>
Create identical copy of one file to another, perform no translation
if no output file is specified, input file will be modified in place
$llvm-objcopy 1.o 1.o.copy–input-target <bfdname>, –output-target <bfdname>
translate from input target to output target
$file 1.o 1.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped $llvm-objcopy --input-target elf32-i386 --output-target elf32-x86-64 1.o 1.o.copy $file 1.o.copy 1.o.copy: ELF 32-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped–add-section <section=file>
insert a section into the output file with name section and contents of file for ELF files, inserted section will be of type SHT_NOTE if section name begins with “.note” otherwise will have type SHT_PROGBITS
$cat insert hello world $llvm-objcopy 1.o 1.o.copy --add-section newSection=insert $llvm-readelf --string-dump newSection String dump of section 'newSection': [ 0] hello world
llvm-ar <options>
Combine several input files into an archive library that can be linked with a program
-cr <output file> <input files>
Create an archive file containing given input files
$ llvm-ar -cr lib.a 1.o 2.o 3.o $ file lib.a lib.a: current ar archive-t <archive>
list archive objects in an archive file
$ llvm-ar -cr lib.a 1.o 2.o 3.o $ llvm-ar -t lib.a 1.o 2.o 3.o-x <archive> <files>
extract files from archive
$ ls lib.a $ llvm-ar -t lib.a 1.o 2.o 3.o $ llvm-ar -x lib.a 1.o 2.o $ ls 1.o 2.o lib.a
llvm-strings <options> <files>
Dump printable strings from binary files to stdout
no-args <files>
Dump printable strings from input file(s) to stdout. If no file is specified, stdin is used
$ cat 1.c $ void foo() {printf("hello world\n");} $ clang 1.c -c hello world clang version 8.0.0 (tags/RELEASE_800/final) .rela.text .comment .note.GNU-stack .llvm_addrsig printf .rela.eh_frame .strtab .symtab .rodata.str1.1–print-file-name <files>
Display the file containing the string before each string
$llvm-strings 1.o a.out 1.o: hello world ... 1.o: .strtab 1.o: .symtab 1.o: .rodata.str1.1 a.out: /lib64/ld-linux-x86-64.so.2 a.out: libc.so.6 a.out: printf a.out: __libc_start_main ... a.out: __frame_dummy_init_array_entry