汇编链接报错：ld无法找到入口符号_start问题求助

Let’s walk through the most likely reasons your linker is throwing that warning, even after you’ve added section directives:

• You’re not generating the right object file format
  Most assemblers (like NASM) don’t default to producing ELF objects (the format ld expects for linking on Linux/Unix-like systems). If you just run nasm yourfile.s without specifying the format, it’ll output a flat binary instead—this file doesn’t contain symbol tables, so ld can’t find _start at all.
  Fix this by explicitly setting the output format when assembling:

  nasm -f elf64 yourfile.s  # For 64-bit systems
  # OR
  nasm -f elf32 yourfile.s  # For 32-bit systems
  

• Your _start label isn’t in the .text section (or the section is misdeclared)
  Even if you added section .text, the placement matters. Make sure _start lives inside the .text section, and your global declaration is correctly scoped. Here’s the correct structure for NASM:

  section .text
  global _start  # Declare _start as a global symbol
  _start:
      # Your assembly instructions go here
  

  If _start is outside the .text section (or you used a typo like segment .text instead of section .text on some assemblers), the linker might not recognize it as a valid entry point.

• You’re mixing assembler syntaxes
  If you’re using GNU Assembler (as) instead of NASM, the syntax for declaring sections and global symbols is different. For as, your code should look like this:

  .section .text
  .global _start
  _start:
      # Your instructions here (using AT&T syntax)
  

  If you wrote NASM-style syntax (like global instead of .global) but used as to assemble, the assembler won’t mark _start as a global symbol—so ld can’t see it.

• Case sensitivity or typos
  Double-check that you didn’t accidentally capitalize _start (like _Start or _START). Linkers and assemblers are case-sensitive on most systems, so a single typo will break the symbol lookup.

• Unintended linker script overrides
  While your command (ld -o assemblyCode assembly.o -g) doesn’t include any, if you’ve ever used a custom linker script or added the -e flag to specify a different entry point in the past, make sure those aren’t lingering in your workflow. The -e flag tells ld to use a specific symbol instead of _start.

Start with the first fix (checking your assembly command and output format)—that’s the most common culprit for this issue.

内容的提问来源于stack exchange，提问作者John