Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> writes: > On 21 January 2016 at 07:45, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote: >> On 21 January 2016 at 06:10, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote: >>> Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> writes: >>>> This implements text-relative kallsyms address tables. This was developed >>>> as part of my series to implement KASLR/CONFIG_RELOCATABLE for arm64, but >>>> I think it may be beneficial to other architectures as well, so I am >>>> presenting it as a separate series. >>> >>> Nice work! >>> >> >> Thanks >> >>> AFAICT this should work for every arch, as long as they start with _text >>> (esp: data and init must be > _text). In addition, it's not harmful on >>> 32 bit archs. >>> >>> IOW, I'd like to turn it on for everyone and discard some code. But >>> it's easier to roll in like you've done first. >>> >>> Should we enable it by default for every arch for now, and see what >>> happens? >>> >> >> As you say, this only works if every symbol >= _text, which is >> obviously not the case per the conditional in scripts/kallsyms.c, >> which emits _text + n or _text - n depending on whether the symbol >> precedes or follows _text. The git log tells me for which arch this >> was originally implemented, but it does not tell me which other archs >> have come to rely on it in the meantime. >> >> On top of that, ia64 fails to build with this option, since it has >> some whitelisted absolute symbols that look suspiciously like they >> could be emitted as _text relative (and it does not even matter in the >> absence of CONFIG_RELOCATABLE on ia64, afaict) but I don't know >> whether we can just override their types as T, since it would also >> change the type in the contents of /proc/kallsyms. So some guidance >> would be appreciated here. >> > > Digging a little deeper, it appears that it would be non-trivial to > port this to ia64: > > ... > a000000000040720 A __kernel_syscall_via_break > a000000000040740 A __kernel_sigtramp > a000000000040a00 A __kernel_syscall_via_epc > a000000100000000 T ia64_ivt > a000000100000000 T __start_ivt_text > a000000100000000 T _stext > a000000100000000 T _text > ... > > The top three symbols are the absolute symbols that are explicitly > whitelisted by scripts/kallsyms.c, and they are too far from 0 and too > far from _text to be representable in 32 bits How annoying. OK, until ia64 is removed, we'll leave the option. Thanks, Rusty. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
