[Xen-devel] [PATCH 2/3] tests/x86emul: Save and restore FPU state in the emulator callbacks

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Currently with then native toolchain on Debian Jessie ./test_x86_emulator
yeilds:

  Testing AVX2 256bit single native execution...okay
  Testing AVX2 256bit single 64-bit code sequence...[line 933] failed!

The bug is that libc's memcpy() in read() uses %xmm8 (specifically, in
__memcpy_sse2_unaligned()), which corrupts %ymm8 behind the back of the AVX2
test code.

Switch all hooks to use "goto out" style returns, and use
emul_{save,restore}_fpu_state().

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
---
 tools/tests/x86_emulator/test_x86_emulator.c | 94 +++++++++++++++++++++++-----
 1 file changed, 79 insertions(+), 15 deletions(-)

diff --git a/tools/tests/x86_emulator/test_x86_emulator.c 
b/tools/tests/x86_emulator/test_x86_emulator.c
index 625cd2a..a764d99 100644
--- a/tools/tests/x86_emulator/test_x86_emulator.c
+++ b/tools/tests/x86_emulator/test_x86_emulator.c
@@ -226,6 +226,10 @@ static int read(
     unsigned int bytes,
     struct x86_emulate_ctxt *ctxt)
 {
+    int rc = X86EMUL_OKAY;
+
+    emul_save_fpu_state();
+
     if ( verbose )
         printf("** %s(%u, %p,, %u,)\n", __func__, seg, (void *)offset, bytes);
 
@@ -236,42 +240,61 @@ static int read(
     case x86_seg_gdtr:
         /* Fake system segment type matching table index. */
         if ( (offset & 7) || (bytes > 8) )
-            return X86EMUL_UNHANDLEABLE;
+        {
+            rc = X86EMUL_UNHANDLEABLE;
+            goto out;
+        }
 #ifdef __x86_64__
         if ( !(offset & 8) )
         {
             memset(p_data, 0, bytes);
-            return X86EMUL_OKAY;
+            goto out;
         }
         value = (offset - 8) >> 4;
 #else
         value = (offset - 8) >> 3;
 #endif
         if ( value >= 0x10 )
-            return X86EMUL_UNHANDLEABLE;
+        {
+            rc = X86EMUL_UNHANDLEABLE;
+            goto out;
+        }
         value |= value << 40;
         memcpy(p_data, &value, bytes);
-        return X86EMUL_OKAY;
+        goto out;
 
     case x86_seg_ldtr:
         /* Fake user segment type matching table index. */
         if ( (offset & 7) || (bytes > 8) )
-            return X86EMUL_UNHANDLEABLE;
+        {
+            rc = X86EMUL_UNHANDLEABLE;
+            goto out;
+        }
         value = offset >> 3;
         if ( value >= 0x10 )
-            return X86EMUL_UNHANDLEABLE;
+        {
+            rc = X86EMUL_UNHANDLEABLE;
+            goto out;
+        }
         value |= (value | 0x10) << 40;
         memcpy(p_data, &value, bytes);
-        return X86EMUL_OKAY;
+        goto out;
 
     default:
         if ( !is_x86_user_segment(seg) )
-            return X86EMUL_UNHANDLEABLE;
+        {
+            rc = X86EMUL_UNHANDLEABLE;
+            goto out;
+        }
         bytes_read += bytes;
         break;
     }
     memcpy(p_data, (void *)offset, bytes);
-    return X86EMUL_OKAY;
+
+ out:
+    emul_restore_fpu_state();
+
+    return rc;
 }
 
 static int fetch(
@@ -281,10 +304,15 @@ static int fetch(
     unsigned int bytes,
     struct x86_emulate_ctxt *ctxt)
 {
+    emul_save_fpu_state();
+
     if ( verbose )
         printf("** %s(%u, %p,, %u,)\n", __func__, seg, (void *)offset, bytes);
 
     memcpy(p_data, (void *)offset, bytes);
+
+    emul_restore_fpu_state();
+
     return X86EMUL_OKAY;
 }
 
@@ -295,13 +323,25 @@ static int write(
     unsigned int bytes,
     struct x86_emulate_ctxt *ctxt)
 {
+    int rc = X86EMUL_OKAY;
+
+    emul_save_fpu_state();
+
     if ( verbose )
         printf("** %s(%u, %p,, %u,)\n", __func__, seg, (void *)offset, bytes);
 
     if ( !is_x86_user_segment(seg) )
-        return X86EMUL_UNHANDLEABLE;
+    {
+        rc = X86EMUL_UNHANDLEABLE;
+        goto out;
+    }
+
     memcpy((void *)offset, p_data, bytes);
-    return X86EMUL_OKAY;
+
+ out:
+    emul_restore_fpu_state();
+
+    return rc;
 }
 
 static int cmpxchg(
@@ -312,13 +352,25 @@ static int cmpxchg(
     unsigned int bytes,
     struct x86_emulate_ctxt *ctxt)
 {
+    int rc = X86EMUL_OKAY;
+
+    emul_save_fpu_state();
+
     if ( verbose )
         printf("** %s(%u, %p,, %u,)\n", __func__, seg, (void *)offset, bytes);
 
     if ( !is_x86_user_segment(seg) )
-        return X86EMUL_UNHANDLEABLE;
+    {
+        rc = X86EMUL_UNHANDLEABLE;
+        goto out;
+    }
+
     memcpy((void *)offset, new, bytes);
-    return X86EMUL_OKAY;
+
+ out:
+    emul_restore_fpu_state();
+
+    return rc;
 }
 
 static int read_segment(
@@ -326,11 +378,23 @@ static int read_segment(
     struct segment_register *reg,
     struct x86_emulate_ctxt *ctxt)
 {
+    int rc = X86EMUL_OKAY;
+
+    emul_save_fpu_state();
+
     if ( !is_x86_user_segment(seg) )
-        return X86EMUL_UNHANDLEABLE;
+    {
+        rc = X86EMUL_UNHANDLEABLE;
+        goto out;
+    }
+
     memset(reg, 0, sizeof(*reg));
     reg->p = 1;
-    return X86EMUL_OKAY;
+
+ out:
+    emul_restore_fpu_state();
+
+    return rc;
 }
 
 static int read_msr(
-- 
2.1.4


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