[U-Boot] Relocation size penalty calculation

Peter Tyser
2009-10-08T16:15:00Z

On Thu, 2009-10-08 at 08:53 -0700, J. William Campbell wrote:
> Peter Tyser wrote:
> > On Thu, 2009-10-08 at 22:54 +1100, 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
> >>
> >> Have any metrics been done for PPC?
> >>
> >
> > Things actually improve a little bit when we use -mrelocatable and get
> > rid of all the manual "+= gd->reloc_off" fixups:
> >
> > 1) Top of mainline on XPedite5370:
> > text data bss dec hex filename
> > 308612 24488 33172 366272 596c0 u-boot
> >
> > 2) Top of "reloc" branch on XPedite5370 (ie -mrelocatable):
> > text data bss dec hex filename
> > 303704 28644 33156 365504 593c0 u-boot
> >
> >
> Hi Peter,
> Just to be clear, the total text+data length of u-boot with the
> "manual" relocations (#1) is LARGER than the text+data length of u-boot
> with the "manual" relocations removed and the necessary centralized
> relocation code added, along with any additional data sections required
> by -mrelocateable (#2), by 768 (dec) bytes?

Hi Bill,
Doah, looks like I chose a bad board as an example. The XPedite5370
already had -mrelocatable defined in its own
board/xes/xpedite5370/config.mk in mainline, so the above comparison
should be ignored as both builds used -mrelocatable.

Here's some *real* results from the MPC8548CDS:
1) Top of mainline:
text data bss dec hex filename
219968 17052 22992 260012 3f7ac u-boot

2) Top of "reloc" branch (ie -mrelocatable)
text data bss dec hex filename
219192 20640 22980 262812 4029c u-boot

So the reloc branch is 2.7K bigger for the MPC8548CDS.

Best,
Peter