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Re: [PATCH 2/4] x86: reduce CET-SS related #ifdef-ary

On 27.07.2020 17:00, Roger Pau Monné wrote:
On Wed, Jul 15, 2020 at 12:48:46PM +0200, Jan Beulich wrote:
Commit b586a81b7a90 ("x86/CET: Fix build following c/s 43b98e7190") had
to introduce a number of #ifdef-s to make the build work with older tool
chains. Introduce an assembler macro covering for tool chains not
knowing of CET-SS, allowing some conditionals where just SETSSBSY is the
problem to be dropped again.

No change to generated code.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Looks like an improvement overall in code clarity:

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>


Can you test on clang? Just to be on the safe side, otherwise I can
test it.

Works with 5.<whatever> that I have on one of my boxes.

--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -237,9 +237,7 @@ iret_exit_to_guest:
   * %ss must be saved into the space left by the trampoline.
          ALTERNATIVE "", "setssbsy", X86_FEATURE_XEN_SHSTK

Should the setssbsy be quoted, or it doesn't matter? I'm asking
because the same construction used by CLAC/STAC doesn't quote the

I actually thought we consistently quote these. It doesn't matter
as long as it's a single word. Quoting becomes necessary when
there are e.g. blanks involved, which happens for insns with




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