"J. William Campbell" jwilliamcampbell@comcast.net wrote on 13/10/2009 18:30:43:
Joakim Tjernlund wrote:
Graeme Russ graeme.russ@gmail.com wrote on 13/10/2009 13:21:05:
On Sun, Oct 11, 2009 at 11:51 PM, Joakim Tjernlund joakim.tjernlund@transmode.se wrote:
Graeme Russ graeme.russ@gmail.com wrote on 11/10/2009 12:47:19:
[Massive Snip :)]
So, all that is left are .dynsym and .dynamic ... .dynsym - Contains 70 entries (16 bytes each, 1120 bytes) - 44 entries mimic those entries in .got which are not relocated - 21 entries are the remaining symbols exported from the linker script - 4 entries are labels defined in inline asm and used in C
Try adding proper asm declarations. Look at what gcc generates for a function/variable and mimic these.
Thanks - Now .dynsym contains only exports from the linker script
:)
- 1 entry is a NULL entry.dynamic - 88 bytes - Array of Elf32_Dyn - typedef struct { Elf32_Sword d_tag; union { Elf32_Word d_val; Elf32_Addr d_ptr; } d_un; } Elf32_Dyn; - 0x11 entries [00] 0x00000010, 0x00000000 DT_SYMBOLIC, (ignored) [01] 0x00000004, 0x38059994 DT_HASH, points to .hash [02] 0x00000005, 0x380595AB DT_STRTAB, points to .dynstr [03] 0x00000006, 0x3805BDCC DT_SYMTAB, points to .dynsym [04] 0x0000000A, 0x000003E6 DT_STRSZ, size of .dynstr [05] 0x0000000B, 0x00000010 DT_SYMENT, ??? [06] 0x00000015, 0x00000000 DT_DEBUG, ??? [07] 0x00000011, 0x3805A8F4 DT_REL, points to .rel.text [08] 0x00000012, 0x000014D8 DT_RELSZ, ???
How big DT_REL is
[09] 0x00000013, 0x00000008 DT_RELENT, ???hmm, cannot remeber :)
How big an entry in DT_REL is
Right, how could I forget :)
[0a] 0x00000016, 0x00000000 DT_TEXTREL, ???Oops, you got text relocations. This is generally a bad thing. TEXTREL is commonly caused by asm code that arent truly pic so it needs to modify the .text segment to adjust for relocation. You should get rid of this one. Look for DT_TEXTREL in .o files to find the culprit.
Alas I cannot - The relocations are a result of loading a register with a return address when calling show_boot_progress in the very early stages of initialisation prior to the stack becoming available. The x86 does not allow direct access to the IP so the only way to find the 'current execution address' is to 'call' to the next instruction and pop the return address off the stack
hmm, same as ppc but that in it self should not cause a TEXREL, should it? Ahh, the 'call' is absolute, not relative? I guess there is some way around it but it is not important ATM I guess.
Evil idea, skip -fpic et. all and add the full reloc procedure to relocate by rewriting directly in TEXT segment. Then you save space but you need more relocation code. Something like dl_do_reloc from uClibc. Wonder how much extra code that would be? Not too much I think.
I think this approach will turn out to be a big win. At present, the problem with just using the relocs is that objcopy is stripping them out when u-boot.bin is created, as I understand it. It seems this can be solved by changing the command switches appropriately, like using --strip-unneeded. In any case, there is some combination of switches that will preserve the relocation data. The executable code will get smaller, there will be no .got, and the relocation data will be larger (than with -fpic). In total size, it probably will be slightly smaller, but that is a guess. The most important benefit of this approach is that it will work for all architectures, thereby solving the problem once and forever! Even if the result is a bit larger, the RAM footprint will be reduced by the smaller object code size (since the relocation data need not be copied into ram).Having this approach as an option would be real nice, since it would always "just work".
Yes, I had this in the back of my head. I do think some other arch than ppc will have to try this out though :) I am not 100% sure this will work with my end goal, true PIC so I can load the same img anywhere in flash.
Jocke