Laurent Desnogues schrieb: > On Sun, Oct 18, 2009 at 5:09 AM, Jamie Lokier <ja...@shareable.org> wrote: > [...] >> Please don't do that. Some code traces instructions through the >> vsyscall/vdso page, and will be surprised if a syscall instruction >> does not do what's expected based on the registers at that point. >> >> Also I don't know if anyone's done this, but I have played with the >> idea of an optimising x86->x86 JIT translator (similar to valgrind or >> qemu's TCG) which would include the vdso instruction sequence in it's >> traces, just because it didn't treat that any differently from other >> userspace code. Making the syscall instruction behave differently due >> to EIP would break that sort of thing. >> >> There's no performance penalty in setting a few registers prior to >> using the syscall instruction normally, so please do that. > > My proposed patch intercepts vsyscall as soon as the PC is > in the [VSYSCALL_START, VSYSCALL_END[ range, so all > instructions in that range won't be translated. Doing it > differently will cause problems due to the virtual address. > >> On x86_64, the vsyscall page has fixed address (see >> linux/arch/x86/kernel/vsyscall_64.c), but the vdso usually has >> variable address. >> >> On x86_32, the vdso has randomised address unless configurd to be a >> fixed address. On older kernels it was a fixed address and some >> binary programs assume they can call that. > > So QEMU can't do things properly and some binaries will > fail, right? > > > Laurent
I can confirm that some binaries fail: x86_64-linux-user/qemu-x86_64 ./bntest with bntest from openssl creates a core dump. Will Laurent's patch be applied, or is there a better way to fix the problem? Stefan
