On Tue, Nov 10, 2009 at 1:29 AM, Richard Sandiford <rdsandiford@xxxxxxxxxxxxxx> wrote: > > I'm not sure I understand the question, sorry. > >> I do not understand how the functions inside a.o, b.o and c.o can >> access the common symbols without duplicating those >> symbols in primary and secondary GOTs . ( I did look at .rel section >> of an exe and did find multiple >> entries for some common symbols like printf ) > > Exactly. That's the point I was trying to make. We sometimes need to > duplicate symbols in order to keep everything within range of a 16-bit > load offset. And the problem is that the ABI-defined, reloc-free GOT > scheme you were asking about only allows a symbol to be mentioned once. > We therefore add secondary GOTs that are (from an ABI point of view) > just "blobs of data" that are relocated by R_MIPS_REL. Those blobs of > data all refer to symbols in the ABI-defined GOT, since every symbol > mentioned in a relocation must also be in the ABI-defined GOT. > > In other words, every entry in a secondary GOT duplicates a symbol > in the ABI-defined GOT. > >> Also, how is the best multigot layout found - the one with least >> duplicated entries ? > > We don't work too hard on that. It's an NP-complete problem. > We just go through each input object in turn and try the following > three things, in order: > > - use the primary GOT > - use the last-used secondary GOT > - create a new secondary GOT > > (This algorithm is from memory, so sorry if I'm oversimplifying.) > > Richard > ok. I have a bit of understanding now. I guess i will have to figure out the rest by some analysis and searching the mailing lists for information . The linker code itself will take much more time to understand. There is no other source of information on MIPS linker internals, I suppose. [ As I mentioned in the first post, my official task is to create some obj files and try to link them into a shared-library This linking should fail due to the reasons that are addressed by the patch posted at http://sourceware.org/ml/binutils/2008-06/msg00270.html . And later, with the patched loader, it should link. So, I have to understand what data and function accesses should be present in the objs for that problem to occur. I won't ask for it ; but I won't mind getting some clue from you. =;) ] thanks shankar
