On Sun, Oct 11, 2009 at 3:18 AM, J. William Campbell <[email protected]> wrote: > Graeme Russ wrote: >> >> On Sat, Oct 10, 2009 at 9:47 PM, Joakim Tjernlund >> <[email protected]> wrote: >> >>> >>> Graeme Russ <[email protected]> wrote on 10/10/2009 12:38:19: >>> >>>> >>>> On Sat, Oct 10, 2009 at 8:27 PM, Joakim Tjernlund >>>> <[email protected]> wrote: >>>> >>>>> >>>>> Graeme Russ <[email protected]> wrote on 10/10/2009 10:46:52: >>>>> >>>>>> >>>>>> On Sat, Oct 10, 2009 at 7:07 PM, Joakim Tjernlund >>>>>> <[email protected]> wrote: >>>>>> >>>>>>> >>>>>>> Graeme Russ <[email protected]> wrote on 10/10/2009 06:43:52: >>>>>>> >>>>>>>> >>>>>>>> On Fri, Oct 9, 2009 at 10:12 AM, Joakim Tjernlund >>>>>>>> <[email protected]> wrote: >>>>>>>> >>>>>>>>>> >>>>>>>>>> On Fri, Oct 9, 2009 at 9:27 AM, J. William Campbell >>>>>>>>>> <[email protected]> wrote: >>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> Graeme Russ wrote: >>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> On Fri, Oct 9, 2009 at 2:58 AM, J. William Campbell >>>>>>>>>>>> <[email protected]> wrote: >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> Graeme Russ wrote: >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> Out of curiosity, I wanted to see just how much of a size >>>>>>>>>>>>>> penalty I am >>>>>>>>>>>>>> incurring by using gcc -fpic / ld -pic on my x86 u-boot build. >>>>>>>>>>>>>> Here are >>>>>>>>>>>>>> the results (fixed width font will help - its space, not tab, >>>>>>>>>>>>>> formatted): >>>>>>>>>>>>>> >>>>>>>>>>>>>> Section non-reloc reloc >>>>>>>>>>>>>> --------------------------------------- >>>>>>>>>>>>>> .text 000118c4 000137fc <- 0x1f38 bytes (~8kB) >>>>>>>>>>>>>> bigger >>>>>>>>>>>>>> .rodata 00005bad 000059d0 >>>>>>>>>>>>>> .interp n/a 00000013 >>>>>>>>>>>>>> .dynstr n/a 00000648 >>>>>>>>>>>>>> .hash n/a 00000428 >>>>>>>>>>>>>> .eh_frame 00003268 000034fc >>>>>>>>>>>>>> .data 00000a6c 000001dc >>>>>>>>>>>>>> .data.rel n/a 00000098 >>>>>>>>>>>>>> .data.rel.ro.local n/a 00000178 >>>>>>>>>>>>>> .data.rel.local n/a 000007e4 >>>>>>>>>>>>>> .got 00000000 000001f0 >>>>>>>>>>>>>> .got.plt n/a 0000000c >>>>>>>>>>>>>> .rel.got n/a 000003e0 >>>>>>>>>>>>>> .rel.dyn n/a 00001228 >>>>>>>>>>>>>> .dynsym n/a 00000850 >>>>>>>>>>>>>> .dynamic n/a 00000080 >>>>>>>>>>>>>> .u_boot_cmd 000003c0 000003c0 >>>>>>>>>>>>>> .bss 00001a34 00001a34 >>>>>>>>>>>>>> .realmode 00000166 00000166 >>>>>>>>>>>>>> .bios 0000053e 0000053e >>>>>>>>>>>>>> ======================================= >>>>>>>>>>>>>> Total 0001d5dd 00022287 <- 0x4caa bytes >>>>>>>>>>>>>> (~19kB) bigger >>>>>>>>>>>>>> >>>>>>>>>>>>>> Its more than a 16% increase in size!!! >>>>>>>>>>>>>> >>>>>>>>>>>>>> .text accounts for a little under half of the total bloat, and >>>>>>>>>>>>>> of that, >>>>>>>>>>>>>> the crude dynamic loader accounts for only 341 bytes >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> Hi Graeme, >>>>>>>>>>>>> I would be interested in a third option (column), the x86 >>>>>>>>>>>>> build with >>>>>>>>>>>>> just -mrelocateable but NOT -fpic. It will not be definitive >>>>>>>>>>>>> because >>>>>>>>>>>>> there >>>>>>>>>>>>> will be extra code that references the GOT and missing code to >>>>>>>>>>>>> do some of >>>>>>>>>>>>> the relocation, but it would still be interesting. >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> x86 does not have -mrelocatable. This is a PPC only option :( >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> Hi Graeme, >>>>>>>>>>> You are unfortunately correct. However, I wonder if we >>>>>>>>>>> can get >>>>>>>>>>> essentially the same result by executing the final ld step with >>>>>>>>>>> the >>>>>>>>>>> --emit-relocs switch included. This may also include some "extra" >>>>>>>>>>> sections >>>>>>>>>>> that we would want to strip out, but if it works, it could give >>>>>>>>>>> all >>>>>>>>>>> ELF-based systems a way to a relocatable u-boot. >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> I don't think --emit-relocs is necessary with -pic. I haven't gone >>>>>>>>>> through >>>>>>>>>> all the permutations to see if there is a smaller option, but gcc >>>>>>>>>> -fpic and >>>>>>>>>> ld -pie creates enough information to perform relocation on the >>>>>>>>>> x86 >>>>>>>>>> platform >>>>>>>>>> >>>>>>>>> >>>>>>>>> Try -fvisibility=hidden >>>>>>>>> >>>>>>>> >>>>>>>> Thanks - Shaved another 2539 bytes off the binary >>>>>>>> >>>>>>>> Also found out how to get rid of .eh_frame (crept in when I upgraded >>>>>>>> to >>>>>>>> gcc 4.4.1) with -fno-dwarf2-cfi-asm, so that shaves another 13452 >>>>>>>> bytes >>>>>>>> >>>>>>>> Total saving of 15.6k >>>>>>>> >>>>>>> >>>>>>> Great, so now you are back at just a few percent added I guess? >>>>>>> >>>>>>> >>>>>>> >>>>>> >>>>>> Not really - The .eh_frame saving applies to both relocated and non >>>>>> relocated builds >>>>>> >>>>> >>>>> OK, so you didn't use PIC before at all? >>>>> >>>>> Anyway I think you can do more. Using -Bsymbolic you should get >>>>> away with RELATIVE relocs only and be able to skip a lot of segments >>>>> above. >>>>> Have a look at uClibc ldso/ldso/dl-startup.c >>>>> >>>>> >>>>> >>>> >>>> My build options thus far are: >>>> >>>> PLATFORM_RELFLAGS += -fpie -fvisibility=hidden >>>> PLATFORM_CPPFLAGS += -fno-dwarf2-cfi-asm >>>> PLATFORM_LDFLAGS += -pie >>>> >>>> -fpic / -pic make no difference >>>> >>> >>> not on x86, on ppc it is a big difference. >>> >>> >>>> >>>> Interestingly, -Bsymbolic adds exactly 8 bytes to .dynamic, but doesn't >>>> change the size of any other section >>>> >>>> Pulling apart the relocation sections, it seems that all relocations are >>>> already RELATIVE even without -Bsymbolic >>>> >>> >>> Ah, that is because you built an exe with -pie >>> Then you should be able to drop everything but the RELATIVE >>> from the linking, or almost in any case. >>> >>> Jocke >>> >>> >>> >> >> Hmm, so its seems I may have hit the limit. I tried: >> >> PLATFORM_LDFLAGS += -r --emit-relocs >> >> but there is not enough information left to complete the relocation. > > Hi Graeme, > I am glad you tried this. It should work, -fpie should not be necessary. > Did you also change PLATFORM_RELFLAGS to omit the -fpie? Without pie, and > with no libraries linked in that are pie, there should BE no .got, AFIK. I > wonder if absolutely everything is getting re-built, like maybe there is a > library routine that is being linked in? What exactly was missing when you > compiled and linked without pie?
I just tried with: PLATFORM_RELFLAGS += -fvisibility=hidden PLATFORM_CPPFLAGS += -fno-dwarf2-cfi-asm PLATFORM_LDFLAGS += -Bsymbolic --emit-relocs There is relocation information in the linker output, however it is not marked for allocation so it gets stripped out when creating u-boot.bin > > Best Regards, > Bill Campbell >> >> It >> seems as though I need .rel.got, .got.plt, .dynsym and .rel.dyn in order >> to find the actual bytes that need modifying (it also seems to mess with >> the size of the stripped binary for some reason) >> >> Looks like I'll have to proceed with my original plan - a bit bloated, >> but it works >> >> Graeme >> >> >> > > _______________________________________________ U-Boot mailing list [email protected] http://lists.denx.de/mailman/listinfo/u-boot
