On Tue, Jul 18, 2017 at 6:33 PM, Thomas Garnier <thgar...@google.com> wrote: > Perpcu uses a clever design where the .percu ELF section has a virtual > address of zero and the relocation code avoid relocating specific > symbols. It makes the code simple and easily adaptable with or without > SMP support. > > This design is incompatible with PIE because generated code always try to > access the zero virtual address relative to the default mapping address. > It becomes impossible when KASLR is configured to go below -2G. This > patch solves this problem by removing the zero mapping and adapting the GS > base to be relative to the expected address. These changes are done only > when PIE is enabled. The original implementation is kept as-is > by default.
The reason the per-cpu section is zero-based on x86-64 is to workaround GCC hardcoding the stack protector canary at %gs:40. So this patch is incompatible with CONFIG_STACK_PROTECTOR. -- Brian Gerst _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
