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[PATCH] x86/alternatives: allow replacement code snippets to be re-used
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 30 Apr 2025 15:13:06 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 30 Apr 2025 13:13:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
In a number of cases we use ALTERNATIVE_2 with both replacement insns /
insn sequences being identical. Avoid emitting the same code twice, and
instead alias the necessary helper labels to the existing ones.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
--- a/xen/arch/x86/include/asm/alternative-asm.h
+++ b/xen/arch/x86/include/asm/alternative-asm.h
@@ -51,6 +51,8 @@
#define decl_repl(insn, nr) .L\@_repl_s\()nr: insn; .L\@_repl_e\()nr:
#define repl_len(nr) (.L\@_repl_e\()nr - .L\@_repl_s\()nr)
+#define clone_repl(new, old) .equiv .L\@_repl_s\()new, .L\@_repl_s\()old; \
+ .equiv .L\@_repl_e\()new, .L\@_repl_e\()old
#define as_max(a, b) ((a) ^ (((a) ^ (b)) & -as_true((a) < (b))))
@@ -100,7 +102,11 @@
.section .altinstr_replacement, "ax", @progbits
decl_repl(\newinstr1, 1)
+ .ifnes "\newinstr2", "\newinstr1"
decl_repl(\newinstr2, 2)
+ .else
+ clone_repl(2, 1)
+ .endif
.popsection
.endm
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