MIPS: Fix handling of long-range spare jumps.

src/lj_asm_mips.h

@@ -64,19 +64,31 @@ static Reg ra_alloc2(ASMState *as, IRIns *ir, RegSet allow)
 /* Setup spare long-range jump slots per mcarea. */
 static void asm_sparejump_setup(ASMState *as)
 {
-  MCode *mxp = as->mcbot;
-  if (((uintptr_t)mxp & (LJ_PAGESIZE-1)) == sizeof(MCLink)) {
+  MCode *mxp = as->mctop;
+  if ((char *)mxp == (char *)as->J->mcarea + as->J->szmcarea) {
+    mxp -= MIPS_SPAREJUMP*2;
     lj_assertA(MIPSI_NOP == 0, "bad NOP");
     memset(mxp, 0, MIPS_SPAREJUMP*2*sizeof(MCode));
-    mxp += MIPS_SPAREJUMP*2;
-    lj_assertA(mxp < as->mctop, "MIPS_SPAREJUMP too big");
-    lj_mcode_sync(as->mcbot, mxp);
-    lj_mcode_commitbot(as->J, mxp);
-    as->mcbot = mxp;
-    as->mclim = as->mcbot + MCLIM_REDZONE;
+    as->mctop = mxp;
   }
 }
 
+static MCode *asm_sparejump_use(MCode *mcarea, MCode tjump)
+{
+  MCode *mxp = (MCode *)((char *)mcarea + ((MCLink *)mcarea)->size);
+  int slot = MIPS_SPAREJUMP;
+  while (slot--) {
+    mxp -= 2;
+    if (*mxp == tjump) {
+      return mxp;
+    } else if (*mxp == MIPSI_NOP) {
+      *mxp = tjump;
+      return mxp;
+    }
+  }
+  return NULL;
+}
+
 /* Setup exit stub after the end of each trace. */
 static void asm_exitstub_setup(ASMState *as)
 {
@@ -2704,21 +2716,17 @@ void lj_asm_patchexit(jit_State *J, GCtrace *T, ExitNo exitno, MCode *target)
 	patchbranch:
 	  p[-1] = (p[-1] & 0xffff0000u) | (delta & 0xffffu);
 	  *p = MIPSI_NOP;  /* Replace the load of the exit number. */
-	  cstop = p;
+	  cstop = p+1;
 	  if (!cstart) cstart = p-1;
 	} else {  /* Branch out of range. Use spare jump slot in mcarea. */
-	  int i;
-	  for (i = (int)(sizeof(MCLink)/sizeof(MCode));
-	       i < (int)(sizeof(MCLink)/sizeof(MCode)+MIPS_SPAREJUMP*2);
-	       i += 2) {
-	    if (mcarea[i] == tjump) {
-	      delta = mcarea+i - p;
-	      goto patchbranch;
-	    } else if (mcarea[i] == MIPSI_NOP) {
-	      mcarea[i] = tjump;
-	      cstart = mcarea+i;
-	      delta = mcarea+i - p;
+	  MCode *mcjump = asm_sparejump_use(mcarea, tjump);
+	  if (mcjump) {
+	    lj_mcode_sync(mcjump, mcjump+1);
+	    delta = mcjump - p;
+	    if (((delta + 0x8000) >> 16) == 0) {
 	      goto patchbranch;
+	    } else {
+	      lj_assertJ(0, "spare jump out of range: -Osizemcode too big");
 	    }
 	  }
 	  /* Ignore jump slot overflow. Child trace is simply not attached. */

src/lj_mcode.c

@@ -314,21 +314,21 @@ void lj_mcode_abort(jit_State *J)
 /* Set/reset protection to allow patching of MCode areas. */
 MCode *lj_mcode_patch(jit_State *J, MCode *ptr, int finish)
 {
-#if LUAJIT_SECURITY_MCODE == 0
-  UNUSED(J); UNUSED(ptr); UNUSED(finish);
-  return NULL;
-#else
   if (finish) {
+#if LUAJIT_SECURITY_MCODE
     if (J->mcarea == ptr)
       mcode_protect(J, MCPROT_RUN);
     else if (LJ_UNLIKELY(mcode_setprot(ptr, ((MCLink *)ptr)->size, MCPROT_RUN)))
       mcode_protfail(J);
+#endif
     return NULL;
   } else {
     MCode *mc = J->mcarea;
     /* Try current area first to use the protection cache. */
     if (ptr >= mc && ptr < (MCode *)((char *)mc + J->szmcarea)) {
+#if LUAJIT_SECURITY_MCODE
       mcode_protect(J, MCPROT_GEN);
+#endif
       return mc;
     }
     /* Otherwise search through the list of MCode areas. */
@@ -336,13 +336,14 @@ MCode *lj_mcode_patch(jit_State *J, MCode *ptr, int finish)
       mc = ((MCLink *)mc)->next;
       lj_assertJ(mc != NULL, "broken MCode area chain");
       if (ptr >= mc && ptr < (MCode *)((char *)mc + ((MCLink *)mc)->size)) {
+#if LUAJIT_SECURITY_MCODE
 	if (LJ_UNLIKELY(mcode_setprot(mc, ((MCLink *)mc)->size, MCPROT_GEN)))
 	  mcode_protfail(J);
+#endif
 	return mc;
       }
     }
   }
-#endif
 }
 
 /* Limit of MCode reservation reached. */