[U-Boot] Relocation size penalty calculation

[J. William Campbell <jwilliamcampbell@comcast.net>]

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? And both cases (1 and 2) 
work equivalently?

Best Regards,
Bill Campbell.
> 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
>
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