[U-Boot] Relocation size penalty calculation

[Peter Tyser]

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

For fun:
3) #2 but with s/-mrelocatable/-fpic/ (probably doesn't boot):
   text	   data	    bss	    dec	    hex	filename
 303704	  24472	  33156	 361332	  58374	u-boot


There may be some other changes that affect the size between mainline
and "reloc", but their sizes are in the same general ballpark.

Best,
Peter