GSoC2008 Stefan Notes

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Contents 1 Notes: Stefan Bucur, Dynamic Module Loading Using the ELF Format 1.1 General Notes 1.2 Useful git techniques 1.3 ELF format notes and links 2 See also

[edit] Notes: Stefan Bucur, Dynamic Module Loading Using the ELF Format

[edit] General Notes

• While searching through glibc source code, I found a very neat piece of code that checks whether a number is a power of two. I've never thought of this before:

/* Must be a power of two.  */
   assert ((bitmask_nwords & (bitmask_nwords - 1)) == 0);

[edit] Useful git techniques

• After you got a little familiar with Git (by reading the tutorial, for instance) and started using it for your project, there might be moments when you feel the need of a more advanced overview of the Git workflow. In that case, I recommend Git in a Nutshell. It briefly explains again the stuff covered in the tutorial, then continues with more advanced techniques that are very likely to be useful for most developers.

[edit] ELF format notes and links

The list below contains sporadic information regarding the ELF format interpretation. As the list grows, I will better organize the items so that one could easily skim through. This list will also be a starting point for a more complete documentation.

• The ultimate source of ELF documentation: http://en.wikipedia.org/wiki/Executable_and_Linkable_Format
• A nicely put together document from the organization that standardized the latest version of ELF: http://x86.ddj.com/ftp/manuals/tools/elf.pdf
• The Linux command readelf is the perfect tool for inspecting ELF objects.
  • readelf -l shows program segment information.
  • readelf -s shows symbol information - there are usually two symbol tables shown, one of them containing symbols pertaining only to dynamic linking - exported symbols, unsatisfied dependencies.
  • readelf -r shows relocation information.
• The Linux command objdump -p sharedobject can also be used to show all the program headers and symbol information in an ELF shared object.
• Some specifications regarding the GNU Hash section (that is said to improve symbol lookup performance by 50%) can be found here: http://sourceware.org/ml/binutils/2006-10/msg00377.html
• The ld documentation is very valuable as it teaches how to craft almost every type of binary with great flexibility.

[edit] See also

• Project Home Page