Re: [Xen-devel] [PATCH 2/10] linux 2.6.18: COMPAT_VDSO

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir@xxxxxxxxxxxxx> 05.03.07 14:42 >>>
>On 5/3/07 11:14, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>
>> This adds support for CONFIG_COMPAT_VDSO. As this will certainly raise
>> questions, I left in the code needed for an alternative approach (which
>> requires mode C code, but less build script changes).
>
>I thought COMPAT_VDSO meant that the VDSO had to be mapped at a fixed
>location at top of memory, which is impossible when running on Xen?

It's gonna be really old libc-s that need an absolutely invariable address. But
you certainly recall that in 2.6.16 (and probably earlier) we had a hack to map
it in right below PAGE_OFFSET, which worked too for not really new but also
not really old libc-s. It is those intermediate libc (supporting AT_SYSINFO but
not AT_SYSINFO_EHDR) versions that the option attempts to address for
Xen. I happen to have a SuSE 9.0 system still in active use that doesn't work
without this option, and I think glibc 2.3.2 shouldn't be considered entirely
obsolete, yet.

Jan

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