In message <[EMAIL PROTECTED]> you wr ote: > On Tue, Aug 19, 2008 at 12:25 AM, Becky Bruce <[EMAIL PROTECTED]> wro te: > > > > On Aug 18, 2008, at 3:51 PM, Michael Neuling wrote: > > > >> In message <[EMAIL PROTECTED]> > >> you wrote: > >>> > >>> The mmu is still disabled at this point. > >>> > >>> What is marked as readonly is the text section of the vmlinux file > >>> generated when compiling the kernel. And since the code tries to write > >>> to the text section, I assumed it was the reason for the segmentation > >>> fault. > >> > >> Seriously, a seg fault in your emulator is a bug in the emulator! > > > > Mikey is likely right here. I've (unfortunately) done a lot of emulator > > work, and every time I've hit a problem like this, the problem has been wit h > > the emulator or the emulation environment. Have you isolated the faulting > > instruction, verified that it's to a reasonable address, and tried examinin g > > memory at the faulting address using your emulator's command interface? > > > > yes, it's a store instruction. the value to be stored is a nop > instruction and the > address is inside the text section (it is writing over existing code that > is intended for other cpus). > > >> > >> > >>> I'm not sure how this is dealt with on real hardware. > >> > >> The CPU seg faults... :-P > > > > But only if the page is mapped non-writeable. Even with the MMU on, Linux > > maps itself in as writeable. It's the OS, it can do whatever it wants. So > > it just works on real hardware, and it should just work in your emulator. > > > > I forgot to mention that I'm trying to run directly the vmlinux image > in psim emulator. > I'm not sure it's even supposed to work this way.
Looking at the psim web page quickly, it seems to be for userspace binaries. So yeah, I don't think it's designed to be used like you are try to use it. > > >> > >> > >>> Can somebody please explain how is it supposed to work ? Is it ok to > >>> write to text section that you load on real hardware as readonly ? > >>> (again, no mmu involved, as it is still turned off, so i'm not sure > >>> who's guarding this section against writing) > >> > >> I'm not sure how this works for 32 bit CPUs, so I can't speak to the > >> details of it. > >> > >> For the 64bit MMU, if you're in real mode (MMU off), nothing can stop > >> this from being written. The kernel ignores the elf sections > >> permissions and does it's own mapping but this can only be enforced once > >> the MMU is on. > > > > The same is true on 32-bit ppc - the basic MMU architecture is very similar > > if you have a part that has "real mode" (i.e. non-booke). There is no way > > to restrict stores in real mode. > > > > -Becky > > > >> > >> > >> Mikey > >> > >>> On Mon, Aug 18, 2008 at 10:19 PM, Michael Neuling <[EMAIL PROTECTED]> > >>> wrote: > >>>> > >>>> In message <[EMAIL PROTECTED]> > >>>> you > >> > >> wrote: > >>>>> > >>>>> Hello, > >>>>> > >>>>> First, I'm talkin about the 2.6.11 version. I know arch/ppc is gone in > >>>>> latest versions, > >>>>> but i assume the code is still the same and just moved to powerpc. > >>>>> > >>>>> There is a piece of code in the early initialization of the 2.6 kernel > >>>>> that identifies the cpu type and then tries to eliminate code that > >>>>> does not apply to the current cpu. This is done by writing nop's over > >>>>> sections of code that are not needed (do_cpu_ftr_fixups in > >>>>> arch/ppc/kernel/misc.S) > >>>>> > >>>>> When I try to run the kernel in a ppc emulator, I get a segmentation > >>>>> fault in do_cpu_ftr_fixups. From examining the section headers of the > >>>>> vmlinux, the text section is marked as readonly. The piece of code > >>>>> above mentioned is trying to write a nop to memory location inside the > >>>>> text section which is readonly, so that explains the sigsegv error. > >>>> > >>>> Any segv in the emulator sounds like a bug in the emulator. > >>>> > >>>> If the page really is marked read only, then writing to it should cause > >>>> a page fault. > >>>> > >>>>> Since the kernel does run on boards with ppc cpu's, can somebody > >>>>> explain how come this is actually working ? Or if/where I am mistaking > >>>>> with my assumptions ? > >>>>> > >>>>> Thank you > >>>>> > >>>>> P.S. please add me in cc in a reply to this message > >>>>> _______________________________________________ > >>>>> Linuxppc-dev mailing list > >>>>> Linuxppc-dev@ozlabs.org > >>>>> https://ozlabs.org/mailman/listinfo/linuxppc-dev > >>>>> > >>>> > >>> > >> _______________________________________________ > >> Linuxppc-dev mailing list > >> Linuxppc-dev@ozlabs.org > >> https://ozlabs.org/mailman/listinfo/linuxppc-dev > > > > > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@ozlabs.org > https://ozlabs.org/mailman/listinfo/linuxppc-dev > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
