Le Sat, 17 Dec 2011 13:26:02 -0500, Boris Gjenero <boris.gjen...@gmail.com> a écrit :
> It seems there's interest in automatically removing unused code via > --gc-sections. Theoretically, the requirements are easy: > > --gc-sections requires KEEP() in linker scripts around things that need > to be kept but are not directly referenced. This only seems to affect > vectors, because they're only accessed by the CPU. > > -ffunction-sections requires wildcards for .text, because it puts > functions in sections like ".text.functionname". > > -fdata-sections similarly requires wildcards for .data, .rodata and > .bss. I don't see a benefit from -fdata-sections due to very little > removed data and added alignment padding. However, I think adding what's > required to allow it to work is a good idea because it's simple. I think jhMikeS already did that part in r31337 (wow, how come we missed that revision?) > Here's a patch which does all that: > http://www.rockbox.org/tracker/task/12378?getfile=24520 . I'm not > certain that it's wise to touch linker scripts that aren't used for > regular target and bootloader builds, but KEEP() shouldn't cause any > harm. I only added wildcards to firmware/rom.lds, because only that is > required to make this work with normal builds. Looks straightforward to me, I think you should just commit it > When something is explicitly put into a particular section, it won't be > automatically moved into a subsection. For example, this includes things > put into .icode via ICODE_ATTR. Such things will only be removed if > nothing else in the same section in the same object file is referenced. > Wildcards for such sections aren't required unless something has been > explicitly moved into a sub-section. Maybe it's a good idea to use > something like ICODE_ATTR("functionname") in the future? I could add > wildcards for that if desired. Yep i think it sounds cool > Builds using these switches shouldn't significantly increase load for > the build infrastructure. However, when the switches are first enabled, > all object files should be re-created to ensure they all use > -ffunction-sections. > > I don't have a patch to add -ffunction-sections to GCCOPTS and > -Wl,--gc-sections to GLOBAL_LDOPTS because I'm not sure how they should > be added. My results at > https://docs.google.com/spreadsheet/ccc?key=0AsEpnuZKewlIdHMteloydnV2eERmWjZsTV9OT2w0UWc > > imply that it should work for all those targets. However, it may be > better to be cautious and only enable it for selected tested targets. > > I think the linker scripts could use some cleanup and merging. I didn't > get around to that, and I don't think making these changes will make > future cleanup and merging harder. Yeah I think they are separate changes but indeed a linker template would be cool and avoid copy/pasted stuff > Regards, > > Boris -- Rafaël Carré
