Newer versions of binutils are capable of emitting an exact number bytes worth
of optimised nops. Use this in preference to .skip when available.
Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
CC: Roger Pau Monné <roger....@citrix.com>
CC: Wei Liu <wei.l...@citrix.com>
RFC until support is actually committed to binutils mainline.
---
xen/arch/x86/Rules.mk | 1 +
xen/include/asm-x86/alternative-asm.h | 16 +++++++++++++---
xen/include/asm-x86/alternative.h | 17 ++++++++++++-----
3 files changed, 26 insertions(+), 8 deletions(-)
diff --git a/xen/arch/x86/Rules.mk b/xen/arch/x86/Rules.mk
index 56b2ea8..c3b726c 100644
--- a/xen/arch/x86/Rules.mk
+++ b/xen/arch/x86/Rules.mk
@@ -20,6 +20,7 @@ $(call as-insn-check,CFLAGS,CC,"invept
(%rax)$$(comma)%rax",-DHAVE_GAS_EPT)
$(call as-insn-check,CFLAGS,CC,"rdrand %eax",-DHAVE_GAS_RDRAND)
$(call as-insn-check,CFLAGS,CC,"rdfsbase %rax",-DHAVE_GAS_FSGSBASE)
$(call as-insn-check,CFLAGS,CC,"rdseed %eax",-DHAVE_GAS_RDSEED)
+$(call as-insn-check,CFLAGS,CC,".nop 0$$(comma)9",-DHAVE_GAS_LONG_NOPS)
$(call as-insn-check,CFLAGS,CC,".equ \"x\"$$(comma)1", \
-U__OBJECT_LABEL__ -DHAVE_GAS_QUOTED_SYM \
'-D__OBJECT_LABEL__=$(subst $(BASEDIR)/,,$(CURDIR))/$$@')
diff --git a/xen/include/asm-x86/alternative-asm.h
b/xen/include/asm-x86/alternative-asm.h
index f7e37cb..a4893e7 100644
--- a/xen/include/asm-x86/alternative-asm.h
+++ b/xen/include/asm-x86/alternative-asm.h
@@ -1,6 +1,8 @@
#ifndef _ASM_X86_ALTERNATIVE_ASM_H_
#define _ASM_X86_ALTERNATIVE_ASM_H_
+#include <asm/nops.h>
+
#ifdef __ASSEMBLY__
/*
@@ -18,6 +20,14 @@
.byte \pad_len
.endm
+.macro mknops nr_bytes
+#ifdef HAVE_GAS_LONG_NOPS
+ .nop \nr_bytes, ASM_NOP_MAX
+#else
+ .skip \nr_bytes, 0x90
+#endif
+.endm
+
#define orig_len (.L\@_orig_e - .L\@_orig_s)
#define pad_len (.L\@_orig_p - .L\@_orig_e)
#define total_len (.L\@_orig_p - .L\@_orig_s)
@@ -29,7 +39,7 @@
.L\@_orig_s:
\oldinstr
.L\@_orig_e:
- .skip (-((repl_len(1) - orig_len) > 0) * (repl_len(1) - orig_len)), 0x90
+ mknops (-((repl_len(1) - orig_len) > 0) * (repl_len(1) - orig_len))
.L\@_orig_p:
.pushsection .altinstructions, "a", @progbits
@@ -56,8 +66,8 @@
.L\@_orig_s:
\oldinstr
.L\@_orig_e:
- .skip (-((gas_max(repl_len(1), repl_len(2)) - orig_len) > 0) * \
- (gas_max(repl_len(1), repl_len(2)) - orig_len)), 0x90
+ mknops (-((gas_max(repl_len(1), repl_len(2)) - orig_len) > 0) * \
+ (gas_max(repl_len(1), repl_len(2)) - orig_len))
.L\@_orig_p:
.pushsection .altinstructions, "a", @progbits
diff --git a/xen/include/asm-x86/alternative.h
b/xen/include/asm-x86/alternative.h
index 20dea22..076d700 100644
--- a/xen/include/asm-x86/alternative.h
+++ b/xen/include/asm-x86/alternative.h
@@ -2,7 +2,6 @@
#define __X86_ALTERNATIVE_H__
#include <asm/alternative-asm.h>
-#include <asm/nops.h>
#ifndef __ASSEMBLY__
#include <xen/stringify.h>
@@ -27,6 +26,14 @@ extern void apply_alternatives(const struct alt_instr *start,
const struct alt_instr *end);
extern void alternative_instructions(void);
+asm ( ".macro mknops nr_bytes\n\t"
+#ifdef HAVE_GAS_LONG_NOPS
+ ".nop \\nr_bytes, " __stringify(ASM_NOP_MAX) "\n\t"
+#else
+ ".skip \\nr_bytes, 0x90\n\t"
+#endif
+ ".endm\n\t" );
+
#define repl_s(num) ".L%=_repl_s"#num
#define repl_e(num) ".L%=_repl_e"#num
@@ -39,8 +46,8 @@ extern void alternative_instructions(void);
#define OLDINSTR_1(oldinstr, n1) \
".L%=_orig_s:\n\t" oldinstr "\n .L%=_orig_e:\n\t" \
- ".skip (-(("alt_repl_len(n1)"-"alt_orig_len") > 0) * " \
- "("alt_repl_len(n1)"-"alt_orig_len")), 0x90\n\t" \
+ "mknops (-(("alt_repl_len(n1)"-"alt_orig_len") > 0) * " \
+ "("alt_repl_len(n1)"-"alt_orig_len"))\n\t" \
".L%=_orig_p:\n\t"
#define ALT_PADDING_LEN(n1, n2) \
@@ -48,8 +55,8 @@ extern void alternative_instructions(void);
#define OLDINSTR_2(oldinstr, n1, n2) \
".L%=_orig_s:\n\t" oldinstr "\n .L%=_orig_e:\n\t" \
- ".skip (-(("ALT_PADDING_LEN(n1, n2)") > 0) * " \
- "("ALT_PADDING_LEN(n1, n2)")), 0x90\n\t" \
+ "mknops (-(("ALT_PADDING_LEN(n1, n2)") > 0) * " \
+ "("ALT_PADDING_LEN(n1, n2)"))\n\t" \
".L%=_orig_p:\n\t"
#define ALTINSTR_ENTRY(feature, num) \
--
2.1.4
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