[U-Boot] Relocation size penalty calculation

Joakim Tjernlund
2009-10-08T23:12:21Z

>
> 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

Jocke