> As revealed by the recent "Prevent data exception in kernel > space" patch, versions of glibc prior to 2.4[1] assume that,
Are you sure that this hasn't been fixed somewhere in the 2.3 series, too? > on powerpc32, they can execute out of any readable mapping, > regardless of whether it is marked for execution. This happens > in the elf_machine_load_address() function. > > To maintain compatibility with these versions, we could change > the test in do_page_fault() to include VM_READ as well as VM_EXEC > on targets that don't have a separate exec-bit in hardware (are > there any powerpc mmus that do?). However, Segher suggested on > IRC that we may want to drop compatibility with those old versions > of glibc, and that I should seek your input. "drop compatibility" -- this sounds worse than it is, this is all about supporting a badly broken application. I wonder how this works with 32-bit userland on a 64-bit kernel, or with older kernels. With arch/ppc/ an exec fault would do the read checks IIRC, maybe we need to change to that. > Personally, I'd rather stick the VM_READ in there, partially for > selfish reasons (our root filesystems are based on older glibcs), > and because it seems a little too soon to deprecate glibc 2.3, Oh I don't know, can't we just deprecate glibc completely? ;-) > but also because in the absence of hardware support, the VM_EXEC > check will be nondeterministic, kicking in only when the first > fault for a page is to execute. I don't think that is a big concern. > [1] It's possible that there are other instances of this in 2.4 and > that the actual version is newer; I ran into obnoxious cross > compilation issues trying to try it. However, <rant>"Trying to try it" sounds like compiling glibc, indeed.</rant> > <rant> > Glibc already has target-specific code/headers; if you need to know > something that you'd otherwise need a runs-on-the-target autoconf > test for, why not just stick it in such a target-specific header? > In this case, it was trying to figure out the size of "long double". > </rant> You can do a test like this by cross-compiling some code, and looking at the size of the symbol in the resulting object file. Well that's all off-topic here. Segher _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
