How can I make GCC compile the .text section as writable in an ELF binary?

by

In the general sense, mprotect is the perferred choice (on POSIX conforming systems) under sys/mman.h (check http://linux.die.net/man/2/mprotect). Simply get the address and system page count of the executable section of your process and call mprotect to request permission permissions; write to it; then, call mprotect again to release write permission.

However, if this is meant to be on low-level routines where speed is of absolute importance (or mprotect is not available) then you’ll want to compile the library with its .text section writable as calling mprotect most likely issues a Translation Lookaside Buffer (TLB) flush that (especially in a multi-processor environment) can and will cause a bottleneck. If the specific system is using hardware protection via paging (which nearly all are now) then the only way to change the protection is by doing a TLB flush which must be executed on every referenced page, referenced page table (group of pages), referenced page directory (group of page tables) and every processor. To top it off, this must be executed in ring 0 which requires a syscall which just puts the cherry on top for overhead.

In the latter case, the easiest solution would be to compile the library normally and then objcopy it with --writable-text (as mentioned by ggiroux).

Another solution would be to define the linker map file linker.ld yourself. Then you may specify permissions of any section explicitly. Its not too complicated; if system-dependent. Refer to documentation at http://www.math.utah.edu/docs/info/ld_3.html. You could also look at your system provided linker.ld file and modify it from there. Passing -Wl,--verbose to gcc will instruct the linker to spit out all relevant files (including its default linker.ld) in which you could then modify the permissions of the .text section and recompile the library (forevermore) using the new linker.ld file.

To summarize, my recommendation would be to do as the last paragraph states and compile your library with a slightly modified linker script.

More Related Contents:

  1. C/C++ with GCC: Statically add resource files to executable/library
  2. What does exactly the warning mean about hidden symbol being referenced by DSO?
  3. Why does integer overflow on x86 with GCC cause an infinite loop?
  4. Capturing function exit time with __gnu_mcount_nc
  5. Why is my program slow when looping over exactly 8192 elements?
  6. C++ syntax for explicit specialization of a template function in a template class?
  7. Error “undefined reference to ‘std::cout'”
  8. How to compile for Windows on Linux with gcc/g++?
  9. GCC STL bound checking
  10. std::stoi doesn’t exist in g++ 4.6.1 on MinGW
  11. Why does gcc compiler output pow(10,2) as 99 not 100? [duplicate]
  12. When and how to use GCC’s stack protection feature?
  13. Search a vector of objects by object attribute
  14. undefined reference to `__stack_chk_fail’
  15. Update GCC on OSX
  16. How do you disable the unused variable warnings coming out of gcc in 3rd party code I do not wish to edit?
  17. error: use of deleted function
  18. g++ How to get warning on ignoring function return value
  19. SetJmp/LongJmp: Why is this throwing a segfault?
  20. Why does `int ;` compile fine in C, but not in C++?
  21. Range based for-loop on array passed to non-main function
  22. GCC C++ pow accuracy
  23. Can I link a plain file into my executable? [duplicate]
  24. What is “strip” (GCC application) used for?
  25. What does -fPIC mean when building a shared library?
  26. Static and Dynamic/Shared Linking with MinGW
  27. Difference between regex_match and regex_search?
  28. Why does sqrt() work fine on an int variable if it is not defined for an int?
  29. Multiple “could not be resolved” problems using Eclipse with minGW
  30. Undefined reference to process(std::__cxx11::basic_string … ) when compiling affdex linux sample applications

Leave a Comment