As Jan Waclawek wrote: > Could you please point me at it, I can't find it. I can find a > mention of pm in > http://www.nongnu.org/avr-libc/user-manual/assembler.html (although > not its modifications documented in the as documentation); but I > can't find explanation of gs.
You're right, the explanation of gs is missing. > However, I did find this: > http://gcc.gnu.org/ml/gcc-patches/2006-05/msg00534.html > which says, among others: > "In order to distinguish relocs where stubs should be generated and relocs > where no stubs should be generated, there are now two new ldi-type PM relocs > that > carry the GS suffix instead of PM. Gas now knows of the directives gs() that > has the same functionality as pm(), only that it generates the GS relocs that > force the linker to generate stubs." OK, so you found all the documentation that we've got about it. :-/ (Now I even understand what "GS" stands for "generate stubs".) > It is sort of Greek to me, though; not really something I would call > user documentation (as I said, I do have a faint idea what those > things do, but I like things to be straight and solid). Did you understand the pm operator? Basically, it's performing a shift operation by one bit, which is needed since all the code addresses in flash are meant to be in units of 16-bit words, while everything else (including all the GNU tools) "think" in units of 8-bit bytes. The pm operator works at the linker level, so it can accept relocatable symbols (where the actual address is inserted by the linker after resolving the relocation). That's why it requires the introduction of a relocation code within the object file, so the assembler can transfer that information to the linker. That's also the reason why you cannot perform the bit shift directly in assembly language: neither the ELF file format nor the GNU linker has any method to transfer that bit shifting into the linker, as there is no support for performing arbitrary arithmetics on relocational symbols. (Well, the linker used on the PDP-11, running RSX-11 did have the ability to do that. But that's been 30 years ago. ;-) For machines with <= 128 KiB of flash ROM, the gs operator works the same. For larger machines, it tells the linker to perform special actions on the data labelled that way, so the linker can take care to handle addresses beyond the current 128 KiB segment where a trampoline entry is needed. (Disclaimer: that's how *I* understood it. Bjoern might correct me here...) > Btw., isn't Bjoern Haase subscribed to this forum? He seems to be > the right person to be pestered for the proper docs... Yes, he is, but I'm afraid he might have unsubscribed some time ago. :-( [Mfile] > Oh, and we even provided the patch this time! ;-) Okay, not a formal > one, but it's just inserting 3 lines anyway. Appreciated, be sure. > > I'm not quite satisfied with that situation, but Mfile is just > > such a minor thing so I'm a little reluctant about pushing it up > > into a full-blown savannah or sourceforge project of its own. > I believe it could be simply sticked to avr-libc. I already thought about that as on option, yes. Might be a good compromise, indeed. -- cheers, J"org .-.-. --... ...-- -.. . DL8DTL http://www.sax.de/~joerg/ NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-) _______________________________________________ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
