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ECS150-L6

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📗 -> 01/16/26: ECS150-L6

Lecture 3
Lec 4

🎤 Vocab

❗ Unit and Larger Context

Discussion:

  • Covering project 1.2

Lect:

  • Sys Calls and Signals
  • file_descriptors.c - Demo, showing file descriptors
    • Linux, everything is a file. Writing to term echo hello > dev/pts/23
      • Inside /proc/617894/fd/ ?
    • He also includes file_descriptors.txtto describe the code in words
  • Starting on lec4, OS structure

✒️ -> Scratch Notes

Signals

Form of interprocess communication (IPC)
About 30 diff signals (man 7 signals)

OS Structure

Apps:

User function calls, by programmers (int main type things)

Libraries (in C)

Declaration:

  • via standard headers
    Definition
  • pre compiled objects (libc.so.6, libc.a, libm.so)
  • input to linker (gcc -lc -lm)
    Code inclusion
  • included in exec directly (gcc -static)
  • or resolved at load-time

Compilation

GCC can pre-process, compile, assemble and link together

  • Preprocessor (cpp) transform program before compilation
    • .c -> .i
    • script.i
  • Compiler (cc) compiles a program into assembly code
    • .i -> .s
      • Assembly, readable but obtuse
    • script.s
  • Assembler (as) compiles assembly code into relocatable object file
    • .s -> .o
      • Binary, not human readable
    • script.o
  • Linker (ld) links object files into an executable
    • script (or a.out)
Linking

Generally loaded dynamically (unless compiled statically)
Can check dependencies:
$ ldd a.out # outputs libraries it needs

Aside: .so files are shared object files. They are compiled library files. The same as Windows DLL

Dynamic:

$ gcc cos.c -lm
$ ldd a.out
	libm.so.6
	libc.so.6
	/lib64/ld-linux-x86-64.so.2
$ ls -sh a.out
16K a.out
$ ./a.out 2.0 
-0.416147

Static

$ gcc -static cos.c -lm 
$ ldd a.out 
not a dynamic executable 
$ ls -sh a.out 
852K a.out 
$ ./a.out 2.0 
-0.416147

Static compilation MASSIVELY increased the file size

🧪 -> Refresh the Info

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🔗 -> Links

Resources

  • Put useful links here

Connections

  • Link all related words

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