Add a workaround for clang bug and remove misleading comment (sparc)

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Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-3.1-pull-request' into staging

Add a workaround for clang bug and remove misleading comment (sparc)

# gpg: Signature made Thu 18 Oct 2018 20:00:17 BST
# gpg:                using RSA key F30C38BD3F2FBE3C
# gpg: Good signature from "Laurent Vivier <lvivier@redhat.com>"
# gpg:                 aka "Laurent Vivier <laurent@vivier.eu>"
# gpg:                 aka "Laurent Vivier (Red Hat) <lvivier@redhat.com>"
# Primary key fingerprint: CD2F 75DD C8E3 A4DC 2E4F  5173 F30C 38BD 3F2F BE3C

* remotes/vivier2/tags/linux-user-for-3.1-pull-request:
  linux-user/sparc/signal.c: Remove unnecessary comment
  linux-user: Suppress address-of-packed-member warnings in __get/put_user_e

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

linux-user/qemu.h

@@ -461,27 +461,59 @@ static inline int access_ok(int type, abi_ulong addr, abi_ulong size)
    These are usually used to access struct data members once the struct has
    been locked - usually with lock_user_struct.  */
 
-/* Tricky points:
+/*
-   - Use __builtin_choose_expr to avoid type promotion from ?:,
+ * Tricky points:
-   - Invalid sizes result in a compile time error stemming from
+ * - Use __builtin_choose_expr to avoid type promotion from ?:,
-     the fact that abort has no parameters.
+ * - Invalid sizes result in a compile time error stemming from
-   - It's easier to use the endian-specific unaligned load/store
+ *   the fact that abort has no parameters.
-     functions than host-endian unaligned load/store plus tswapN.  */
+ * - It's easier to use the endian-specific unaligned load/store
+ *   functions than host-endian unaligned load/store plus tswapN.
+ * - The pragmas are necessary only to silence a clang false-positive
+ *   warning: see https://bugs.llvm.org/show_bug.cgi?id=39113 .
+ * - We have to disable -Wpragmas warnings to avoid a complaint about
+ *   an unknown warning type from older compilers that don't know about
+ *   -Waddress-of-packed-member.
+ * - gcc has bugs in its _Pragma() support in some versions, eg
+ *   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83256 -- so we only
+ *   include the warning-suppression pragmas for clang
+ */
+#ifdef __clang__
+#define PRAGMA_DISABLE_PACKED_WARNING                                   \
+    _Pragma("GCC diagnostic push");                                     \
+    _Pragma("GCC diagnostic ignored \"-Wpragmas\"");                    \
+    _Pragma("GCC diagnostic ignored \"-Waddress-of-packed-member\"")
 
-#define __put_user_e(x, hptr, e)                                        \
+#define PRAGMA_REENABLE_PACKED_WARNING          \
-  (__builtin_choose_expr(sizeof(*(hptr)) == 1, stb_p,                   \
+    _Pragma("GCC diagnostic pop")
-   __builtin_choose_expr(sizeof(*(hptr)) == 2, stw_##e##_p,             \
+
-   __builtin_choose_expr(sizeof(*(hptr)) == 4, stl_##e##_p,             \
+#else
-   __builtin_choose_expr(sizeof(*(hptr)) == 8, stq_##e##_p, abort))))   \
+#define PRAGMA_DISABLE_PACKED_WARNING
-     ((hptr), (x)), (void)0)
+#define PRAGMA_REENABLE_PACKED_WARNING
+#endif
+
+#define __put_user_e(x, hptr, e)                                            \
+    do {                                                                    \
+        PRAGMA_DISABLE_PACKED_WARNING;                                      \
+        (__builtin_choose_expr(sizeof(*(hptr)) == 1, stb_p,                 \
+        __builtin_choose_expr(sizeof(*(hptr)) == 2, stw_##e##_p,            \
+        __builtin_choose_expr(sizeof(*(hptr)) == 4, stl_##e##_p,            \
+        __builtin_choose_expr(sizeof(*(hptr)) == 8, stq_##e##_p, abort))))  \
+            ((hptr), (x)), (void)0);                                        \
+        PRAGMA_REENABLE_PACKED_WARNING;                                     \
+    } while (0)
+
+#define __get_user_e(x, hptr, e)                                            \
+    do {                                                                    \
+        PRAGMA_DISABLE_PACKED_WARNING;                                      \
+        ((x) = (typeof(*hptr))(                                             \
+        __builtin_choose_expr(sizeof(*(hptr)) == 1, ldub_p,                 \
+        __builtin_choose_expr(sizeof(*(hptr)) == 2, lduw_##e##_p,           \
+        __builtin_choose_expr(sizeof(*(hptr)) == 4, ldl_##e##_p,            \
+        __builtin_choose_expr(sizeof(*(hptr)) == 8, ldq_##e##_p, abort))))  \
+            (hptr)), (void)0);                                              \
+        PRAGMA_REENABLE_PACKED_WARNING;                                     \
+    } while (0)
 
-#define __get_user_e(x, hptr, e)                                        \
-  ((x) = (typeof(*hptr))(                                               \
-   __builtin_choose_expr(sizeof(*(hptr)) == 1, ldub_p,                  \
-   __builtin_choose_expr(sizeof(*(hptr)) == 2, lduw_##e##_p,            \
-   __builtin_choose_expr(sizeof(*(hptr)) == 4, ldl_##e##_p,             \
-   __builtin_choose_expr(sizeof(*(hptr)) == 8, ldq_##e##_p, abort))))   \
-     (hptr)), (void)0)
 
 #ifdef TARGET_WORDS_BIGENDIAN
 # define __put_user(x, hptr)  __put_user_e(x, hptr, be)

linux-user/sparc/signal.c

@@ -258,10 +258,6 @@ void setup_frame(int sig, struct target_sigaction *ka,
         __put_user(val32, &sf->insns[1]);
         if (err)
             goto sigsegv;
-
-        /* Flush instruction space. */
-        // flush_sig_insns(current->mm, (unsigned long) &(sf->insns[0]));
-        // tb_flush(env);
     }
     unlock_user(sf, sf_addr, sizeof(struct target_signal_frame));
     return;