Dynamic Link Walking (Linux only)

[Ex-32]

Dynamic Link Walking

parsing ELF files, reading environment variables, and traversing the filesystem to produce a runtime link dependency tree before an executable is exec-ed

Approximate roadmap

• ELF parsing
  • 64-bit
    • section table parsing
    • dynamic section parsing
    • dynamic string table parsing
    • program segment table parsing
    • interpreter segment parsing
  • 32-bit
    • section table parsing
    • dynamic section parsing
    • dynamic string table parsing
    • program segment table parsing
    • interpreter segment parsing
• dependency searching
  • environment variable aggregation
  • RPATH and RUNPATH aggregation
  • RPATH and RUNPATH substitutions
  • filesystem traversal
• recursive evaluation
  • propagate RPATH
• cry about added overhead

[charmoniumQ]

This seems reasonable; hopefully the 64-bit logic is not too different than the 32-bit.

Regarding overhead, hopefully it's not too bad, since the loader will now have a warmed cache (we aren't loading anything they wouldn't). Also, I am hoping to use statistics to separate the cost-per-exec vs cost-per-other-things.

[Ex-32]

hopefully the 64-bit logic is not too different than the 32-bit.

It shouldn't be: the structs and alignments are all different, but the fields are almost all the same, so like 90% of the work will probably be copy, paste, s/64/32/g