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GSoC 2007 - Codesize Reduction Project

Things done so far

This is a summary of the things I did so far (including those that didn't work), in roughly chronological order.

  • Get LXR running and use it on the Etherboot source.

Status: Didn't seem as useful as I had hoped. Will revisit and investigate other options once I get to the full attribute makeover.

  • Go through other programs and check their Makefiles to discover potentially interesting compiler options.

Status: (Re)discovered the extremly useful stack alignment option in the Linux Kernel.

          Has been the biggest win so far, already merged.
* check effects of some other options, write script for mass compiles with different sets, another one to compare the effects.
  Status: useful options checked in to gccopt branch. separate branch for packed enums. (not merged yet) (more on the not so useful ones later, if i can still figure them out)
* prepare code for conversion to regparm option
  Status: went through the code, located the functions that need standard calling conventions. committed to gccopt branch, not merged (or reviewed) yet. hope i got them all.

alternative may be attributing individual functions, but as i can't imagine a case where it's not a win, just attributing those where it must not be used should be better.

  • prepare zalloc changes, go through all occurences of malloc and see if that memory is cleared soon after.

Status: branch merged (think i got them all, had some false positives at first though → reverted)

  • go through make symcheck output, make appropriate changes to code

Status: went through a lot of output, picked the ones that seem not too controversial,

  checked in to symcheck branch. (not merged yet). Further plan is addressing the problem
  at the root and reduce the symcheck output by eliminating false positives, then address
  the remaining unclear ones (i do not claim to understand all the code i have read ;)
  No real solution discovered (yet), hackish ideas (eliminate by suffix, eliminate by
  exporting another symbol that says false positive) set aside for now. did research if
  better tools than nm and objdump exist, haven't found any yet.
* test malloc attribute in preparation for the complete go-through all attributes.
  unfortunately no difference at all. local branch exists, may be included in the attr
  changes for completeness.

somewhere in between: install git, learn to use it, research documentation on attributes (found a nice page, will include the link later)

Things to do in the second half of GSoC

  • Use LXR on current master, look into other tools if necessary (OpenGROK still looks

nice, but I haven't set it up so far)

  • start annotating functions with attributes. (may be a large amount of work that might

not lead to anything useful, but at least we know that then - and it might inspire

  ideas on other modifications to commonly used functions)
* continue thinking about the symcheck problem.
* write up some docs for the conversions that helped, give some background, maybe 
  illustrated by examples of the generated code before and after.
* write up docs on when functions (or other symbols) should be attributed by what.
* whatever else comes up

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