[U-Boot] Relocation size penalty calculation

J. William Campbell
2009-10-08T22:27:47Z

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.

Best Regards,
Bill Campbell
**
>
>
>> Best Regards,
>> Bill Campbell
>>
>>> Have any metrics been done for PPC?
>>>
>>> Regards,
>>>
>>> Graeme
>>>
>
> Once the reloc branch has been merged, how many arches are left which do
> not support relocation?
>
> Regards,
>
> Graeme
>
>
>