[Xen-devel] [PATCH] xen/x86: Improve hypercall page writing

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Use memcpy() rather than individual writes with explicit casts.  The
__builtin_memcpy() wrapper does a better job at combining adjacent writes into
a larger word size.

This results in better generated assembly.  No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
CC: Kevin Tian <kevin.tian@xxxxxxxxx>
CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
CC: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
---
 xen/arch/x86/hvm/svm/svm.c         | 10 +++++-----
 xen/arch/x86/hvm/vmx/vmx.c         | 10 +++++-----
 xen/arch/x86/x86_64/compat/traps.c | 15 +++++++++------
 xen/arch/x86/x86_64/traps.c        | 31 ++++++++++++++++++-------------
 4 files changed, 37 insertions(+), 29 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 811ea4e..962667a 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -888,12 +888,12 @@ static void svm_init_hypercall_page(struct domain *d, 
void *hypercall_page)
             continue;
 
         p = (char *)(hypercall_page + (i * 32));
-        *(u8  *)(p + 0) = 0xb8; /* mov imm32, %eax */
+        *(u8  *)(p + 0) = 0xb8; /* mov $<i>, %eax */
         *(u32 *)(p + 1) = i;
-        *(u8  *)(p + 5) = 0x0f; /* vmmcall */
-        *(u8  *)(p + 6) = 0x01;
-        *(u8  *)(p + 7) = 0xd9;
-        *(u8  *)(p + 8) = 0xc3; /* ret */
+        memcpy(p + 5,
+               "\x0f\x01\xd9"   /* vmmcall */
+               "\xc3",          /* ret */
+               4);
     }
 
     /* Don't support HYPERVISOR_iret at the moment */
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index d50d49e..c0e62a2 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1295,12 +1295,12 @@ static void vmx_init_hypercall_page(struct domain *d, 
void *hypercall_page)
             continue;
 
         p = (char *)(hypercall_page + (i * 32));
-        *(u8  *)(p + 0) = 0xb8; /* mov imm32, %eax */
+        *(u8  *)(p + 0) = 0xb8; /* mov $<i>, %eax */
         *(u32 *)(p + 1) = i;
-        *(u8  *)(p + 5) = 0x0f; /* vmcall */
-        *(u8  *)(p + 6) = 0x01;
-        *(u8  *)(p + 7) = 0xc1;
-        *(u8  *)(p + 8) = 0xc3; /* ret */
+        memcpy(p + 5,
+               "\x0f\x01\xc1"   /* vmmcall */
+               "\xc3",          /* ret */
+               4);
     }
 
     /* Don't support HYPERVISOR_iret at the moment */
diff --git a/xen/arch/x86/x86_64/compat/traps.c 
b/xen/arch/x86/x86_64/compat/traps.c
index 95c5cb3..8b03291 100644
--- a/xen/arch/x86/x86_64/compat/traps.c
+++ b/xen/arch/x86/x86_64/compat/traps.c
@@ -388,8 +388,10 @@ static void hypercall_page_initialise_ring1_kernel(void 
*hypercall_page)
         p = (char *)(hypercall_page + (i * 32));
         *(u8  *)(p+ 0) = 0xb8;    /* mov  $<i>,%eax */
         *(u32 *)(p+ 1) = i;
-        *(u16 *)(p+ 5) = (HYPERCALL_VECTOR << 8) | 0xcd; /* int  $xx */
-        *(u8  *)(p+ 7) = 0xc3;    /* ret */
+        memcpy(p + 5,
+               "\xcd\x82" /* int $HYPERCALL_VECTOR */
+               "\xc3",    /* ret */
+               3);
     }
 
     /*
@@ -398,10 +400,11 @@ static void hypercall_page_initialise_ring1_kernel(void 
*hypercall_page)
      * calling it.
      */
     p = (char *)(hypercall_page + (__HYPERVISOR_iret * 32));
-    *(u8  *)(p+ 0) = 0x50;    /* push %eax */
-    *(u8  *)(p+ 1) = 0xb8;    /* mov  $__HYPERVISOR_iret,%eax */
-    *(u32 *)(p+ 2) = __HYPERVISOR_iret;
-    *(u16 *)(p+ 6) = (HYPERCALL_VECTOR << 8) | 0xcd; /* int  $xx */
+    memcpy(p,
+           "\x50"                 /* push %eax */
+           "\xb8\x17\x00\x00\x00" /* mov  $__HYPERVISOR_iret, %eax */
+           "\xcd\x82",            /* int  $HYPERCALL_VECTOR */
+           8);
 }
 
 /*
diff --git a/xen/arch/x86/x86_64/traps.c b/xen/arch/x86/x86_64/traps.c
index fc8cde6..7a586cd 100644
--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -591,14 +591,18 @@ static void hypercall_page_initialise_ring3_kernel(void 
*hypercall_page)
             continue;
 
         p = (char *)(hypercall_page + (i * 32));
-        *(u8  *)(p+ 0) = 0x51;    /* push %rcx */
-        *(u16 *)(p+ 1) = 0x5341;  /* push %r11 */
-        *(u8  *)(p+ 3) = 0xb8;    /* mov  $<i>,%eax */
+        memcpy(p,
+               "\x51"      /* push %rcx */
+               "\x41\x53"  /* push %r11 */
+               "\xb8",     /* mov  $<i>,%eax */
+               4);
         *(u32 *)(p+ 4) = i;
-        *(u16 *)(p+ 8) = 0x050f;  /* syscall */
-        *(u16 *)(p+10) = 0x5b41;  /* pop  %r11 */
-        *(u8  *)(p+12) = 0x59;    /* pop  %rcx */
-        *(u8  *)(p+13) = 0xc3;    /* ret */
+        memcpy(p + 8,
+               "\x0f\x05"  /* syscall */
+               "\x41\x5b"  /* pop  %r11 */
+               "\x59"      /* pop  %rcx */
+               "\xc3",     /* ret */
+               6);
     }
 
     /*
@@ -607,12 +611,13 @@ static void hypercall_page_initialise_ring3_kernel(void 
*hypercall_page)
      * calling it.
      */
     p = (char *)(hypercall_page + (__HYPERVISOR_iret * 32));
-    *(u8  *)(p+ 0) = 0x51;    /* push %rcx */
-    *(u16 *)(p+ 1) = 0x5341;  /* push %r11 */
-    *(u8  *)(p+ 3) = 0x50;    /* push %rax */
-    *(u8  *)(p+ 4) = 0xb8;    /* mov  $__HYPERVISOR_iret,%eax */
-    *(u32 *)(p+ 5) = __HYPERVISOR_iret;
-    *(u16 *)(p+ 9) = 0x050f;  /* syscall */
+    memcpy(p,
+           "\x51"                 /* push %rcx */
+           "\x41\x53"             /* push %r11 */
+           "\x50"                 /* push %rax */
+           "\xb8\x17\x00\x00\x00" /* mov  $__HYPERVISOR_iret,%eax */
+           "\x0f\x05",            /* syscall */
+           11);
 }
 
 #include "compat/traps.c"
-- 
2.1.4


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