[Xen-devel] [PATCH v4 09/24] x86/emul: Provide a wrapper to x86_emulate() to ASSERT() certain behaviour

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

In debug builds, confirm that some properties of x86_emulate()'s behaviour
actually hold.  The first property, fixed in a previous change, is that retire
flags are only ever set in the X86EMUL_OKAY case.

While adjusting the userspace test harness to cope with ASSERT() in
x86_emulate.h, fix a build problem introduced in c/s 122dd9575c7 "x86emul:
in_longmode() should not ignore ->read_msr() errors" by providing an
implementation of likely()/unlikely().

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>

v4:
 * Shuffle #ifdefary
 * Correct the documentation for x86_emulate()
 * Use true/false in likely/unlikely definitions
v3:
 * New
---
 tools/tests/x86_emulator/test_x86_emulator.c |  1 +
 tools/tests/x86_emulator/x86_emulate.c       |  4 +++-
 xen/arch/x86/x86_emulate/x86_emulate.c       |  3 +++
 xen/arch/x86/x86_emulate/x86_emulate.h       | 27 ++++++++++++++++++++++++++-
 4 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/tools/tests/x86_emulator/test_x86_emulator.c 
b/tools/tests/x86_emulator/test_x86_emulator.c
index f255fef..b54fd11 100644
--- a/tools/tests/x86_emulator/test_x86_emulator.c
+++ b/tools/tests/x86_emulator/test_x86_emulator.c
@@ -1,3 +1,4 @@
+#include <assert.h>
 #include <errno.h>
 #include <limits.h>
 #include <stdbool.h>
diff --git a/tools/tests/x86_emulator/x86_emulate.c 
b/tools/tests/x86_emulator/x86_emulate.c
index c46b7fc..897b9ab 100644
--- a/tools/tests/x86_emulator/x86_emulate.c
+++ b/tools/tests/x86_emulator/x86_emulate.c
@@ -16,7 +16,6 @@ typedef bool bool_t;
 #define EFER_LMA       (1 << 10)
 
 #define BUG() abort()
-#define ASSERT assert
 #define ASSERT_UNREACHABLE() assert(!__LINE__)
 
 #if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
@@ -50,4 +49,7 @@ typedef bool bool_t;
 #define __init
 #define __maybe_unused __attribute__((__unused__))
 
+#define likely(x)     __builtin_expect(!!(x), true)
+#define unlikely(x)   __builtin_expect(!!(x), false)
+
 #include "x86_emulate/x86_emulate.c"
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
b/xen/arch/x86/x86_emulate/x86_emulate.c
index bfcc05d..3e602da 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -2404,6 +2404,9 @@ x86_decode(
 #undef insn_fetch_bytes
 #undef insn_fetch_type
 
+/* Undo DEBUG wrapper. */
+#undef x86_emulate
+
 int
 x86_emulate(
     struct x86_emulate_ctxt *ctxt,
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.h 
b/xen/arch/x86/x86_emulate/x86_emulate.h
index ef39601..60f9105 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.h
+++ b/xen/arch/x86/x86_emulate/x86_emulate.h
@@ -23,6 +23,10 @@
 #ifndef __X86_EMULATE_H__
 #define __X86_EMULATE_H__
 
+#if !defined(__XEN__) && !defined(ASSERT)
+#define ASSERT assert
+#endif
+
 #define MAX_INST_LEN 15
 
 struct x86_emulate_ctxt;
@@ -546,13 +550,34 @@ struct x86_emulate_stub {
 
 /*
  * x86_emulate: Emulate an instruction.
- * Returns -1 on failure, 0 on success.
+ * Returns X86EMUL_* constants.
  */
 int
 x86_emulate(
     struct x86_emulate_ctxt *ctxt,
     const struct x86_emulate_ops *ops);
 
+#ifndef NDEBUG
+/*
+ * In debug builds, wrap x86_emulate() with some assertions about its expected
+ * behaviour.
+ */
+static inline int x86_emulate_wrapper(
+    struct x86_emulate_ctxt *ctxt,
+    const struct x86_emulate_ops *ops)
+{
+    int rc = x86_emulate(ctxt, ops);
+
+    /* Retire flags should only be set for successful instruction emulation. */
+    if ( rc != X86EMUL_OKAY )
+        ASSERT(ctxt->retire.raw == 0);
+
+    return rc;
+}
+
+#define x86_emulate x86_emulate_wrapper
+#endif
+
 /*
  * Given the 'reg' portion of a ModRM byte, and a register block, return a
  * pointer into the block that addresses the relevant register.
-- 
2.1.4


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