What does KEEP mean in a linker script?

by

Afaik LD keeps the symbols in the section even if symbols are not referenced. (–gc-sections).

Usually used for sections that have some special meaning in the binary startup process, more or less to mark the roots of the dependency tree.

(For Sabuncu below)

Dependency tree:

If you eliminate unused code, you analyze the code and mark all reachable sections (code+global variables + constants).

So you pick a section, mark it as “used” and see what other (unused) section it references, then you mark those section as “used”, and check what they reference etc.

The section that are not marked “used” are then redundant, and can be eliminated.

Since a section can reference multiple other sections (e.g. one procedure calling three different other ones), if you would draw the result you get a tree.

Roots:

The above principle however leaves us with a problem: what is the “first” section that is always used? The first node (root) of the tree so to speak? This is what “keep()” does, it tells the linker which sections (if available) are the first ones to look at. As a consequence these are always linked in.

Typically these are sections that are called from the program loader to perform tasks related to dynamic linking (can be optional, and OS/fileformat dependent), and the entry point of the program.

More Related Contents:

  1. Limiting visibility of symbols when linking shared libraries
  2. Is accessing the “value” of a linker script variable undefined behavior in C?
  3. How do i clear this issue? unable to compile? [closed]
  4. Why does the order of ‘-l’ option in gcc matter? [duplicate]
  5. What are the –start-group and –end-group command line options?
  6. How to print the ld(linker) search path
  7. combine two GCC compiled .o object files into a third .o file
  8. Why an ELF executable could have 4 LOAD segments?
  9. GNU gcc/ld – wrapping a call to symbol with caller and callee defined in the same object file
  10. Minimal executable size now 10x larger after linking than 2 years ago, for tiny programs?
  11. Linking against older symbol version in a .so file
  12. How do I add contents of text file as a section in an ELF file?
  13. Linking a C program directly with ld fails with undefined reference to `__libc_csu_fini`
  14. How to link to a different libc file?
  15. Can the linker inline functions?
  16. ld linker question: the –whole-archive option
  17. How to make weak linking work with GCC?
  18. Undefined reference to `initscr’ Ncurses
  19. What do C and Assembler actually compile to? [closed]
  20. Undefined reference error for template method [duplicate]
  21. Increase Stack Size on Windows (GCC)
  22. How to create static linked shared libraries
  23. Hierarchical ldd(1)
  24. How to solve ——-undefined reference to `__chkstk_ms’——-on mingw
  25. Compiling multiple C files in a program
  26. What is the use of .exp and what is the difference between .lib and .dll?
  27. Can different GCC dialects be linked together?
  28. cmake – Global linker flag setting (for all targets in directory)
  29. how do compilers assign memory addresses to variables?
  30. Override weak symbols in static library

Leave a Comment