On Tue, 2008-11-04 at 18:48 -0500, Pavel Roskin wrote: > > However, it would be nice to have a better explanation why "-mlongcall" > is needed. If it's only needed for modules and has significant > overhead, we may want to introduce MODULE_CFLAGS, which would only be > used for modules.
It absolutely should only be used for modules. It's needed because a PowerPC branch instruction can only target +/- 32MB. -mlongcall replaces the direct branch with an indirect one (using mtctr/bctrl instructions). This can target the full 32-bit address space. > By the way, I tried cross-compiling for PowerPC with and without > "-mlongcall" with gcc 4.2.4. With "-mlongcall", the size of all modules > combined is 426424 bytes. Without "-mlongcall", the size of all modules > combined is 354464 bytes. That's a significant difference for a > bootloader and should be avoided if possible. To be fair, if we are that worried about footprint, why do we have a runtime ELF linker in a bootloader? At any rate, the point of having dynamically loadable modules is so you can only load the ones you need. On that scale I think the size increase is less of an issue. > Maybe there is a way to keep the modules and the core in the first 32 > megabytes? Actually I'm confused about something here Manoel. Module memory is allocated by grub_malloc(), but as you can see at http://svn.savannah.gnu.org/viewvc/trunk/grub2/kern/ieee1275/init.c?revision=1806&root=grub&view=markup the GRUB heap capped at 4MB (I don't mean size, I mean the end of the heap). So how are your modules appearing in memory above 32MB? -- Hollis Blanchard IBM Linux Technology Center _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org http://lists.gnu.org/mailman/listinfo/grub-devel
