Le 05/10/2010 01:21, Graeme Russ a écrit :
On Tue, Oct 5, 2010 at 9:57 AM, Albert ARIBAUDalbert.aribaud@free.fr wrote:
Le 05/10/2010 00:22, Graeme Russ a écrit :
On Tue, Oct 5, 2010 at 9:01 AM, Albert Aribaudalbert.aribaud@free.fr wrote:
The output from MAKEALL is curiously calculated... If I look at objdumps of the GOT and ELF binaries, I find that:
- the GOT .text section is 118960 bytes and the ELF .text section only
- This is due to the fact that GOT relocation requires additional
instruction for GOT indirection whereas ELF relocations work by patching the code.
It would be interesting to compare against the basline non-relocatable version
I #defined CONFIG_RELOC_FIXUP_WORKS and removed -pie from the ARM config.mk. This puts the edminiv2 code in the non-reloc build case, and produces identical .text and .data, and almost identical .rodata, as the ELF case.
- the .rodata section is 22416 for GOT, 22698 for ELF, whereas the .data
section is 2908 for GOT, 2627 for ELF. Some initialized data apparently moved from non-const ton const for some reason, but basically, initialized data remains constant.
- the .bss section remains constant too, 16640 for GOT vs. 16636 for ELF.
I'm not going to track what causes the 4 byte difference. :)
Many sections are output in the ELF file which do not appear in the GOT file, such as .interp, .dynamic, .dynstr etc. They probably pollute MAKEALL's figures.
I now discard a few sections:
/DISCARD/ : { *(.dynstr*) } /DISCARD/ : { *(.dynamic*) } /DISCARD/ : { *(.plt*) } /DISCARD/ : { *(.interp*) } /DISCARD/ : { *(.gnu*) }
Not that it makes a huge difference - most of these are trivially small
Thanks. I'll add this to the .lds as a measure of clarity.
That's roughly consistent with the numbers I get: about 19 KB of .rel.dyn plus .dynsym, which we will be able to cut by half if we preprocess it.
Which is not copied to RAM, so not as nasty as the .got related increase
True also. Note that we could probably shrink the table to 1/4 of its current size by taking advantage from the fact that the few non-program-base-relative relocations it has can easily be converted to program-base-relative, and that two consecutive relocations are always less than 64 KB away from each other. Of course that moves away from using the ELF structures as-is, and requires additional build steps, but people with small FLASH devices may want it.
I'm also looking at moving the low-level intialisation and relocation code into a seperate section (outside .text) so I even less to relocate to RAM
As Wolfgang pointed out, there might be issues in that all the code that runs in FLASH should be truly PI, which might not be a piece of cake. ARM C code, for instance, tends to generate literals which need to be relocated if you don't run the code where it was linked for.
Then I could even compress the relocatable section, but that is just being silly ;)
:)
Regards,
Graeme
Amicalement,