Messages in this thread | | | Date | Fri, 6 Feb 2004 05:01:23 +0100 | From | Andrea Arcangeli <> | Subject | Re: [RFC][PATCH] linux-2.6.2_vsyscall-gtod_B2.patch |
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On Thu, Feb 05, 2004 at 07:10:46PM -0800, john stultz wrote: > @@ -6,6 +9,8 @@ > .globl __kernel_vsyscall > .type __kernel_vsyscall,@function > __kernel_vsyscall: > + cmp $__NR_gettimeofday, %eax > + je .Lvgettimeofday > .LSTART_vsyscall:
this is the sort of slowdown that could be avoided with the fixed address.
with regards to Ulrich's security related comments, this won't make any difference compared to the fixed address version either, since the vsyscall page is still at a fixed address in the fixmap area, and nevertheless regardless the vgettimeofday api, the sysenter instruction is always placed at a fixed address in the address space for the sysenter vsyscall support, so at the light of the i386 current status, those comments w.r.t to security make even less sense.
This has the feature that it doesn't need the LD_PRELOAD and it's sort of backwards compatible, but it is equivalent in terms of security and as a matter of fact it's less efficient and the worst part is that not only it makes gettimeofday slower, it makes _all_ the syscall slower (slowing down vgettimeofday wouldn't matter since we're improving it huge anyways).
I prefer the previous version, glibc has to be changed at the same time with the kernel anyways to use the sysenter. I think it's not nice to speedup gettimeofday by slowing down all other syscalls, when we can implement it running all syscalls at full speed with the optimal API of x86-64. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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