shithub: mc

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Fix struct alignment.

    We over padded. This was bad for 2 reasons:
        - We wasted memory.
            For structs containing just bytes, we
            almost doubled the memory usage.

        - We were not C compatible.
            Normally I wouldn't care, but for the syscall
            ABIs, our data needs to work.

--- a/6/simp.c

+++ b/6/simp.c

@@ -61,6 +61,11 @@

 static Type *tyword;

 static Type *tyvoid;

+static size_t tyalign(size_t sz, size_t eltsz)

+{

+    return align(sz, min(eltsz, Ptrsz));

+}

+

 static Type *base(Type *t)

 {

     assert(t->nsub == 1);

@@ -300,13 +305,22 @@

             assert(exprop(t->asize) == Olit);

             return t->asize->expr.args[0]->lit.intval * tysize(t->sub[0]);

         case Tytuple:

-            for (i = 0; i < t->nsub; i++)

+            for (i = 0; i < t->nsub; i++) {

+                sz = tyalign(sz, tysize(t->sub[i]));

                 sz += tysize(t->sub[i]);

+            }

+            for (i = 0; i < t->nsub; i++)

+                sz = tyalign(sz, tysize(t->sub[i]));

             return sz;

             break;

         case Tystruct:

+            for (i = 0; i < t->nmemb; i++) {

+                sz = tyalign(sz, size(t->sdecls[i]));

+                sz += size(t->sdecls[i]);

+            }

+            /* the whole struct size should match the biggest alignment */

             for (i = 0; i < t->nmemb; i++)

-                sz += align(size(t->sdecls[i]), Ptrsz);

+                sz = tyalign(sz, size(t->sdecls[i]));

             return sz;

             break;

         case Tyunion:

@@ -522,6 +536,7 @@

             patarg = pat->expr.args;

             off = 0;

             for (i = 0; i < pat->expr.nargs; i++) {

+                off = tyalign(off, size(patarg[i]));

                 next = genlbl();

                 v = load(addk(addr(s, val, exprtype(patarg[i])), off));

                 umatch(s, patarg[i], v, exprtype(patarg[i]), next, iffalse);

@@ -631,6 +646,7 @@

     nl = ty->sdecls;

     off = 0;

     for (i = 0; i < ty->nmemb; i++) {

+        off = tyalign(off, size(nl[i]));

         if (!strcmp(namestr(memb), declname(nl[i])))

             return off;

         off += size(nl[i]);

@@ -930,6 +946,7 @@

     off = 0;

     for (i = 0; i < lhs->expr.nargs; i++) {

         lv = lval(s, args[i]);

+        off = tyalign(off, size(lv));

         prv = add(addr(s, rhs, exprtype(args[i])), disp(rhs->line, off));

         if (stacknode(args[i])) {

             sz = disp(lhs->line, size(lv));

@@ -1008,6 +1025,7 @@

     off = 0;

     for (i = 0; i < n->expr.nargs; i++) {

+        off = tyalign(off, size(args[i]));

         assignat(s, r, off, args[i]);

         off += size(args[i]);

     }