Re: [PATCH v2 09/10] target/i386: implement 32-bit SYSENTER for linux-user

[Paolo Bonzini]

On Tue, Jun 20, 2023 at 6:23 PM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 6/20/23 17:16, Paolo Bonzini wrote:
> > TCG reports the SEP feature (SYSENTER/SYSEXIT) in user mode emulation,
> > but does not plumb it into the linux-user run loop.  Split the helper into
> > system emulation and user-mode emulation cases and implement the latter.
>
> I'm not keen on this.
>
> This belongs with the rest of the vdso (see patches posted years ago; 
> committing binary
> blobs rejected, still waiting on a decent way to invoke cross-compilers to 
> build them).

As we discussed in Dublin, that should be doable by reusing the
tests/tcg logic in configure (though we would likely commit the binary
blobs as well). You could do it in your sleep. ;)

> Further, this shouldn't ever be reachable, because AT_SYSINFO won't be 
> present to give the
> guest libc the location of the vdso routine to call.

Even without AT_SYSINFO the program should be able to do SYSENTER and
'trust" the kernel not to change the epilog of the routine.

To be honest I don't like it particularly either; but I also didn't
like that SEP is reported but doesn't work (and the purpose of these
patches is to allow using named CPU models in linux-user)... I can
certainly drop the patch since it's been like this for ages.

Paolo