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 | 4 ++++
xen/include/asm-x86/alternative-asm.h | 14 ++++++++++++--
xen/include/asm-x86/alternative.h | 13 ++++++++++---
3 files changed, 26 insertions(+), 5 deletions(-)
diff --git a/xen/arch/x86/Rules.mk b/xen/arch/x86/Rules.mk
index e169d67..bf5047f 100644
--- a/xen/arch/x86/Rules.mk
+++ b/xen/arch/x86/Rules.mk
@@ -28,6 +28,10 @@ $(call as-option-add,CFLAGS,CC,".equ \"x\"$$(comma)1", \
$(call as-option-add,CFLAGS,CC,\
".if ((1 > 0) < 0); .error \"\";.endif",,-DHAVE_AS_NEGATIVE_TRUE)
+# Check to see whether the assmbler supports the .nop directive.
+$(call as-option-add,CFLAGS,CC,\
+ ".L1: .L2: .nop (.L2 - .L1)$$(comma)9",-DHAVE_AS_NOP_DIRECTIVE)
+
CFLAGS += -mno-red-zone -fpic -fno-asynchronous-unwind-tables
# Xen doesn't use SSE interally. If the compiler supports it, also skip the
diff --git a/xen/include/asm-x86/alternative-asm.h
b/xen/include/asm-x86/alternative-asm.h
index 25f79fe..9e46bed 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_AS_NOP_DIRECTIVE
+ .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)
@@ -43,7 +53,7 @@
*/
.L\@_diff = repl_len(1) - orig_len
- .skip as_true(.L\@_diff > 0) * .L\@_diff, 0x90
+ mknops (as_true(.L\@_diff > 0) * .L\@_diff)
.L\@_orig_p:
.pushsection .altinstructions, "a", @progbits
@@ -76,7 +86,7 @@
*/
.L\@_diff = as_max(repl_len(1), repl_len(2)) - orig_len
- .skip as_true(.L\@_diff > 0) * .L\@_diff, 0x90
+ mknops (as_true(.L\@_diff > 0) * .L\@_diff)
.L\@_orig_p:
.pushsection .altinstructions, "a", @progbits
diff --git a/xen/include/asm-x86/alternative.h
b/xen/include/asm-x86/alternative.h
index d53cea0..51538b6 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_AS_NOP_DIRECTIVE
+ ".nop \\nr_bytes, " __stringify(ASM_NOP_MAX) "\n\t"
+#else
+ ".skip \\nr_bytes, 0x90\n\t"
+#endif
+ ".endm\n\t" );
+
#define alt_orig_len "(.LXEN%=_orig_e - .LXEN%=_orig_s)"
#define alt_pad_len "(.LXEN%=_orig_p - .LXEN%=_orig_e)"
#define alt_total_len "(.LXEN%=_orig_p - .LXEN%=_orig_s)"
@@ -46,7 +53,7 @@ extern void alternative_instructions(void);
#define OLDINSTR_1(oldinstr, n1) \
".LXEN%=_orig_s:\n\t" oldinstr "\n .LXEN%=_orig_e:\n\t" \
".LXEN%=_diff = "alt_repl_len(n1)"-"alt_orig_len"\n\t" \
- ".skip "AS_TRUE"(.LXEN%=_diff > 0) * .LXEN%=_diff, 0x90\n\t" \
+ "mknops ("AS_TRUE"(.LXEN%=_diff > 0) * .LXEN%=_diff)\n\t" \
".LXEN%=_orig_p:\n\t"
#define ALT_PADDING_LEN(n1, n2) \
@@ -55,7 +62,7 @@ extern void alternative_instructions(void);
#define OLDINSTR_2(oldinstr, n1, n2) \
".LXEN%=_orig_s:\n\t" oldinstr "\n .LXEN%=_orig_e:\n\t" \
".LXEN%=_diff = "ALT_PADDING_LEN(n1, n2)"\n\t" \
- ".skip "AS_TRUE"(.LXEN%=_diff > 0) * .LXEN%=_diff, 0x90\n\t" \
+ "mknops ("AS_TRUE"(.LXEN%=_diff > 0) * .LXEN%=_diff)\n\t" \
".LXEN%=_orig_p:\n\t"
#define ALTINSTR_ENTRY(feature, num) \
--
2.1.4
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