gcc hello.c -o hello gcc behind the scene

from chatGPT

 

i just changed hello.c to hello.sh.
then compile use gcc, it reports error. why?

 

When you issue the command:

gcc hello.c -o hello

GCC performs four major stages by default, unless told otherwise. These are:

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1. Preprocessing

• Tool involved: cpp

• Input: hello.c

• Output: preprocessed source (.i file, internally)

• Purpose:

  • Expands macros (#define)

  • Includes headers (#include)

  • Removes comments

  • Processes conditional compilation (#ifdef, etc.)

✅ Result: a "flattened" version of the C code, ready for parsing.

---

2. Compilation

• Tool involved: cc1

• Input: preprocessed .i file

• Output: assembly code (.s file, internally)

• Purpose:

  • Parses and analyzes the C code

  • Performs syntax and semantic checks

  • Converts C code into architecture-specific assembly language

✅ Result: human-readable assembly instructions (but not yet executable).

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3. Assembly

• Tool involved: as (the assembler)

• Input: assembly file (.s)

• Output: object file (.o)

• Purpose:

  • Converts assembly code into machine code (binary)

  • Produces a relocatable object file (not yet a full program)

✅ Result: raw object code — the actual CPU instructions.

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4. Linking

• Tool involved: ld (the linker)

• Input: object file(s) + standard libraries (e.g., libc)

• Output: executable (hello)

• Purpose:

  • Combines your object file with startup code (crt0), standard libraries (like printf), etc.

  • Resolves symbols (e.g., links main to _start)

  • Produces a complete, executable binary

✅ Result: A self-contained executable program.

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Summary Table:

Stage	Tool	Input	Output	Description
Preprocessing	cpp	hello.c	hello.i	Handles macros, headers, etc.
Compilation	cc1	hello.i	hello.s	C → Assembly
Assembly	as	hello.s	hello.o	Assembly → Object Code
Linking	ld	hello.o, libs	hello	Object code → Executable

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Optional:

You can inspect each stage manually:

gcc -E hello.c -o hello.i     # Only preprocessing
gcc -S hello.c -o hello.s     # Compile to assembly
gcc -c hello.c -o hello.o     # Compile+assemble to object
gcc hello.o -o hello          # Link only

This gives you fine-grained control over the pipeline.

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Would you like a diagram of this pipeline, or want to step through it with a concrete example?