[committed mig] Do not generate code dereferencing type-punned pointers

[Justus Winter]

For variable-length arrays, up to 2048 bytes are transmitted inline.
If the array is larger, the data is transmitted out-of-line, and a
pointer to a vm_allocated region is stored at the beginning of the
array.

Previously, the generated code casted the field.  Use a union instead.

This fixes the gcc warning `dereferencing type-punned pointer will
break strict-aliasing rules [-Wstrict-aliasing]'.

* global.c (OOLPostfix): New variable.
* global.h (OOLPostfix): New declaration.
* server.c (WriteServerCallArg): Avoid cast.
(WriteDestroyArg): Likewise.
(WritePackArgValue): Likewise.
(WritePackArg): Likewise.
* user.c (WriteExtractArgValue): Likewise.
* utils.c (WriteFieldDeclPrim): Generate a union with an additional
pointer field for variable-length arrays.
---
 global.c |  1 +
 global.h |  1 +
 server.c | 18 +++++++++---------
 user.c   |  9 +++++----
 utils.c  |  8 +++++++-
 5 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/global.c b/global.c
index 0a938f2..5685186 100644
--- a/global.c
+++ b/global.c
@@ -48,6 +48,7 @@ const_string_t UserPrefix = "";
 const_string_t ServerDemux = strNULL;
 const_string_t SubrPrefix = "";
 const_string_t RoutinePrefix = "";
+const_string_t OOLPostfix = "P";
 
 string_t yyinname;
 
diff --git a/global.h b/global.h
index ca4d865..8dbb6fd 100644
--- a/global.h
+++ b/global.h
@@ -53,6 +53,7 @@ extern const_string_t UserPrefix;
 extern const_string_t ServerDemux;
 extern const_string_t SubrPrefix;
 extern const_string_t RoutinePrefix;
+extern const_string_t OOLPostfix;
 
 extern int yylineno;
 extern string_t yyinname;
diff --git a/server.c b/server.c
index 56ccfc7..15fc128 100644
--- a/server.c
+++ b/server.c
@@ -777,9 +777,9 @@ WriteServerCallArg(FILE *file, const argument_t *arg)
                    arg->argTTName,
                    arg->argLongForm ? ".msgtl_header" : "");
            fprintf(file, "? %s ", InArgMsgField(arg));
-           fprintf(file, ": *((%s **)%s)",
-                       FetchServerType(arg->argType->itElement),
-                       InArgMsgField(arg));
+           fprintf(file, ": %s%s",
+                   InArgMsgField(arg),
+                   OOLPostfix);
        }
        else
            fprintf(file, "%s", InArgMsgField(arg));
@@ -816,8 +816,8 @@ WriteDestroyArg(FILE *file, const argument_t *arg)
                arg->argRequestPos,
                arg->argTTName,
                arg->argLongForm ? ".msgtl_header" : "");
-       fprintf(file, "\t\t\t%smig_deallocate(* (vm_offset_t *) %s, ",
-               SubrPrefix, InArgMsgField(arg));
+       fprintf(file, "\t\t\t%smig_deallocate((vm_offset_t) %s%s, ",
+               SubrPrefix, InArgMsgField(arg), OOLPostfix);
        if (multiplier > 1)
            fprintf(file, "%d * ", multiplier);
        fprintf(file, " %s);\n", InArgMsgField(count));
@@ -978,9 +978,9 @@ WritePackArgValue(FILE *file, const argument_t *arg)
                            arg->argTTName,
                            arg->argLongForm ? ".msgtl_header" : "",
                            arg->argDealloc->argVarName);
-               fprintf(file, "\t\t*((%s **)OutP->%s) = %sP;\n",
-                       FetchServerType(btype),
+               fprintf(file, "\t\tOutP->%s%s = %sP;\n",
                        arg->argMsgField,
+                       OOLPostfix,
                        arg->argVarName);
                if (!arg->argRoutine->rtSimpleFixedReply)
                    fprintf(file, "\t\tmsgh_simple = FALSE;\n");
@@ -1203,9 +1203,9 @@ WritePackArg(FILE *file, const argument_t *arg)
                        arg->argTTName,
                        arg->argLongForm ? ".msgtl_header" : "",
                        arg->argDealloc->argVarName);
-           fprintf(file, "\t\t*((%s **)OutP->%s) = %sP;\n",
-                       FetchServerType(it->itElement),
+           fprintf(file, "\t\tOutP->%s%s = %sP;\n",
                        arg->argMsgField,
+                       OOLPostfix,
                        arg->argVarName);
            if (!arg->argRoutine->rtSimpleFixedReply)
                fprintf(file, "\t\tmsgh_simple = FALSE;\n");
diff --git a/user.c b/user.c
index 5451a03..1f3ba3d 100644
--- a/user.c
+++ b/user.c
@@ -447,9 +447,9 @@ WritePackArgValue(FILE *file, const argument_t *arg)
                            arg->argLongForm ? ".msgtl_header" : "",
                            arg->argDealloc->argByReferenceUser ? "*" : "",
                            arg->argDealloc->argVarName);
-               fprintf(file, "\t\t*((%s **)InP->%s) = %s%s;\n",
-                       FetchUserType(btype),
+               fprintf(file, "\t\tInP->%s%s = %s%s;\n",
                        arg->argMsgField,
+                       OOLPostfix,
                        ref, arg->argVarName);
                if (!arg->argRoutine->rtSimpleFixedRequest)
                    fprintf(file, "\t\tmsgh_simple = FALSE;\n");
@@ -951,9 +951,10 @@ WriteExtractArgValue(FILE *file, const argument_t *arg)
            fprintf(file, "\tif (!OutP->%s%s.msgt_inline)\n",
                    arg->argTTName,
                    arg->argLongForm ? ".msgtl_header" : "");
-           fprintf(file, "\t    %s%s = *((%s **)OutP->%s);\n",
+           fprintf(file, "\t    %s%s = OutP->%s%s;\n",
                    ref, arg->argVarName,
-                   FetchUserType(btype), arg->argMsgField);
+                   arg->argMsgField,
+                   OOLPostfix);
            fprintf(file, "\telse if (OutP->%s", count->argMsgField);
            if (btype->itNumber > 1)
                fprintf(file, " / %d", btype->itNumber);
diff --git a/utils.c b/utils.c
index 396e743..4c2a87b 100644
--- a/utils.c
+++ b/utils.c
@@ -239,10 +239,16 @@ WriteFieldDeclPrim(FILE *file, const argument_t *arg,
         *      use the element type and maximum size specified.
         *      Note arg->argCount->argMultiplier == btype->itNumber.
         */
-       fprintf(file, "\t\t%s %s[%d];",
+       fprintf(file, "\t\tunion {\n");
+       fprintf(file, "\t\t\t%s %s[%d];\n",
                        (*tfunc)(btype),
                        arg->argMsgField,
                        it->itNumber/btype->itNumber);
+       fprintf(file, "\t\t\t%s *%s%s;\n",
+                       (*tfunc)(btype),
+                       arg->argMsgField,
+                       OOLPostfix);
+       fprintf(file, "\t\t};");
     }
     else
        fprintf(file, "\t\t%s %s;", (*tfunc)(it), arg->argMsgField);
-- 
2.1.4