Add support for jumps to local labels.

Currently limited to 16-bits ONLY.

Allows code like:

|1:
| ...
| j <1

dynasm/Examples/test_z_inst.c

@@ -8,6 +8,7 @@
 // DynASM directives.
 |.arch s390x
 |.actionlist actions
+|.globals lab_
 
 static void add(dasm_State *state)
 {
@@ -61,6 +62,20 @@ static void rxy(dasm_State *state)
   | br r14
 }
 
+static void lab(dasm_State *state)
+{
+  dasm_State **Dst = &state;
+
+  // r1 = 0; do { r2 += r2; r1 += 1; } while(r1 < r3);
+  | la r1, 0(r0)
+  |1:
+  | agr r2, r2
+  | la r1, 1(r1)
+  | cgr r1, r3
+  | jl <1
+  | br r14
+}
+
 typedef struct {
   int64_t arg1;
   int64_t arg2;
@@ -74,7 +89,8 @@ test_table test[] = {
   {10, 5, sub,     5, "sub"},
   { 2, 3, mul,     6, "mul"},
   { 5, 7,  rx, 12298,  "rx"},
-  { 5, 7, rxy,    10, "rxy"}
+  { 5, 7, rxy,    10, "rxy"},
+  { 2, 4, lab,    32, "lab"}
 };
 
 static void *jitcode(dasm_State **state, size_t *size)
@@ -93,9 +109,10 @@ static void *jitcode(dasm_State **state, size_t *size)
 int main(int argc, char *argv[])
 {
   dasm_State *state;
-
   for(int i = 0; i < sizeof(test)/sizeof(test[0]); i++) {
     dasm_init(&state, 1);
+    void* labels[lab__MAX];
+    dasm_setupglobal(&state, labels, lab__MAX);
     dasm_setup(&state, actions);
     test[i].fn(state);
     size_t size;

dynasm/dasm_s390x.h

@@ -219,7 +219,7 @@ void dasm_put(Dst_DECL, int start, ...)
       b[pos++] = ofs;
       break;
     case DASM_REL_LG:
-      n = (ins & 2047) - 10;
+      n = *p++ - 10;
       pl = D->lglabels + n;
       /* Bkwd rel or global. */
       if (n >= 0) {
@@ -247,7 +247,7 @@ void dasm_put(Dst_DECL, int start, ...)
       pos++;
       break;
     case DASM_LABEL_LG:
-      pl = D->lglabels + (ins & 2047) - 10;
+      pl = D->lglabels + *p++ - 10;
       CKPL(lg, LG);
       goto putlabel;
     case DASM_LABEL_PC:
@@ -262,6 +262,7 @@ void dasm_put(Dst_DECL, int start, ...)
       }
       *pl = -pos;               /* Label exists now. */
       b[pos++] = ofs;           /* Store pass1 offset estimate. */
+      ofs += 2;
       break;
     case DASM_IMM16:
       CK(((short)n) == n, RANGE_I);     /* TODO: unsigned immediates? */
@@ -348,10 +349,12 @@ int dasm_link(Dst_DECL, size_t * szp)
           break;
         case DASM_REL_LG:
         case DASM_REL_PC:
+          p++;
           pos++;
           break;
         case DASM_LABEL_LG:
         case DASM_LABEL_PC:
+          p++;
           b[pos++] += ofs;
           break;
         case DASM_IMM16:
@@ -421,13 +424,11 @@ int dasm_encode(Dst_DECL, void *buffer)
           CK(n >= 0, UNDEF_PC);
           n = *DASM_POS2PTR(D, n) - (int)((char *)cp - base);
         patchrel:
-          CK((n & 3) == 0 &&
+          *cp++ = n/2; /* TODO: only 16-bit relative jump currently works. */
-             (((n + 4) + ((ins & 2048) ? 0x00008000 : 0x02000000)) >>
+          p++; /* skip argument */
-              ((ins & 2048) ? 16 : 26)) == 0, RANGE_REL);
-          cp[-1] |= ((n + 4) & ((ins & 2048) ? 0x0000fffc : 0x03fffffc));
           break;
         case DASM_LABEL_LG:
-          ins &= 2047;
+          ins = *p++;
           if (ins >= 20)
             D->globals[ins - 10] = (void *)(base + n);
           break;

dynasm/dasm_s390x.lua

@@ -1057,6 +1057,14 @@ local function parse_template(params, template, nparams, pos)
       op2 = op2 + band(shr(d, 4), 0xff00)
       wputhw(op0); wputhw(op1); wputhw(op2)
       if a then a() end -- a() emits action.
+    elseif p == "w" then
+      local mode, n, s = parse_label(params[1])
+      wputhw(op1)
+      waction("REL_"..mode, n, s)
+    elseif p == "x" then
+      local mode, n, s = parse_label(params[1])
+      wputhw(op0)
+      waction("REL_"..mode, n, s)
     elseif p == "y" then
       local d, x, b, a = parse_mem_bx(params[1])
       op1 = op1 + x
@@ -1066,6 +1074,8 @@ local function parse_template(params, template, nparams, pos)
     elseif p == "z" then
       op2 = op2 + parse_gpr(params[1])
       wputhw(op2)
+    else
+      werror("unrecognized encoding")
     end
   end