On 30 March 2015 at 16:13, Michal Marek <mmarek@xxxxxxx> wrote: > On 2015-03-30 15:31, Ard Biesheuvel wrote: >> On 30 March 2015 at 15:26, Russell King - ARM Linux >> <linux@xxxxxxxxxxxxxxxx> wrote: >>> On Mon, Mar 30, 2015 at 02:38:35PM +0200, Michal Marek wrote: >>>> Is this a limitation of a particular ARM ABI or a limitation of a state >>>> of the art ARM linker or something else? >>> >>> It's a limitation of the ARM ISA. >>> >>> Normal PC-relative branches, which are emitted by the C compiler, can >>> branch +/- 32MB for ARM, or +/- 16MB of Thumb. Beyond that, the address >>> offset is not representable in the instruction. > > Thank you both for the explanation! > > >>> The question is: how far do we go with allyesconfig... do we want it >>> to work, or is reaching the final link sufficient? > > It certainly is more useful as a test tool if the baseline is a > successful compile and link. Because you can have genuine link errors > due to missing symbols. > Agreed > >>> If we do tweak >>> stuff to allow the link to work, are we going to try running it? > > Good question. I myself always treated all{yes,mod}config as a build > test only and never dared to run it. Allyesconfig produces a giant > kernel image and allmodconfig builds binfmt_script as a module. And if > people used all*config for boot tests, they would probably be sending > patches to tweak the Kconfigs for that purpose. And this is not the case > as far as I can tell. > Russell should confirm this, but I think running such a large kernel is non-trivial on ARM, since the decompressor should make room for the decompressed image by moving itself upward in memory, and it may overwrite the device tree binary in the process. > >> That is an excellent question, hence the RFC in the subject line. >> >> Note that the other patch, the one against kallsyms, addresses the >> issue where the distance between the beginning of .text and the end of >> .init.text exceeds this limit, which is not as unlikely as the issue >> that this patch addresses, where just drivers/built-in.o in isolation >> already exceeds this limit. >> >> So I am quite happy to drop this, especially as we can add >> -ffunction-sections as well. > > What you could do is to add a Kconfig option to arch/arm/Kconfig adding > -ffunction-sections to the compiler flags. Then allyesconfig would > select it and work around the problem in a somewhat elegant way. > Excellent idea! Arnd hasn't chimed in yet, but he is the one doing lots and lots of randconfig builds and other test builds, so I will wait for him to confirm that this is a useful thing to have. Thanks, Ard. -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html