Graeme Russ graeme.russ@gmail.com wrote on 10/10/2009 10:46:52:
On Sat, Oct 10, 2009 at 7:07 PM, Joakim Tjernlund joakim.tjernlund@transmode.se wrote:
Graeme Russ graeme.russ@gmail.com wrote on 10/10/2009 06:43:52:
On Fri, Oct 9, 2009 at 10:12 AM, Joakim Tjernlund joakim.tjernlund@transmode.se wrote:
On Fri, Oct 9, 2009 at 9:27 AM, J. William Campbell jwilliamcampbell@comcast.net wrote:
Graeme Russ wrote: > > On Fri, Oct 9, 2009 at 2:58 AM, J. William Campbell > jwilliamcampbell@comcast.net 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