objdump: disasm raw binary

1 files changed, 38 insertions, 0 deletions

diff --git a/src/binary/objdump.md b/src/binary/objdump.md
index 636db3f..a76a327 100644
--- a/src/binary/objdump.md
+++ b/src/binary/objdump.md
@@ -16,3 +16,41 @@ For example `.plt` section:
 ```markdown
   objdump -j .plt -d <elf>
 ```
+
+## Example: disassemble raw binary
+This can be helpful for example as a cheap analysis tool when toying with JIT
+generating code. We could just write thee binary code buffer to a file and
+disassemble with `objdump`.
+
+To re-create that case, we just assemble and link some ELF file and then create
+a raw binary of the text section with `objcopy`.
+
+```x86asm
+# file: test.s
+.section .text, "ax"
+
+.global _start
+_start:
+    xor %rax, %rax
+    mov $0x8, %rax
+1:
+    cmp $0, %rax
+    je 2f
+    dec %rax
+    jmp 1b
+2:
+    # x86-64 exit(2) syscall
+    mov $0, %rdi
+    mov $60, %rax
+    syscall
+```
+```bash
+# Assemble & link.
+as -o test.o test.s
+ld -o test test.o testc.o
+# ELF -> binary (only take .text section).
+objcopy -O binary --only-section .text test test-bin
+
+# Disassemble raw binary.
+objdump -D -b binary -m i386:x86-64 test-bin
+```