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Re: [PATCH 2/2] x86: guard synthetic feature and bug enumerators
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Jason Andryuk <jason.andryuk@xxxxxxx>
- Date: Tue, 7 Oct 2025 15:38:32 -0400
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 07 Oct 2025 19:39:04 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2025-10-07 08:22, Jan Beulich wrote:
On 30.09.2025 01:36, Jason Andryuk wrote:
On 2025-09-25 06:48, Jan Beulich wrote:
--- a/xen/arch/x86/include/asm/spec_ctrl.h
+++ b/xen/arch/x86/include/asm/spec_ctrl.h
@@ -73,7 +73,7 @@ static always_inline void spec_ctrl_new_
/* (ab)use alternative_input() to specify clobbers. */
alternative_input("", "DO_OVERWRITE_RSB xu=%=", X86_BUG_IBPB_NO_RET,
- : "rax", "rcx");
+ "i" (0) : "rax", "rcx");
"i" (0) is to work around the trailing comma in alternative_input() and
does nothing?
Yes. If more such "uses" appeared, we may want to introduce some kind of
abstraction.
Thanks for confirming.
Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
Though I also wondered if just #define X86_BUG_MAX/X86_SYNTH_MAX
combined with a BUILD_BUG_ON might be good enough. Your approach avoids
the extra define but is more complicated. Anyway, just a thought.
Regards,
Jason
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