i386: do not cross the pages boundaries in replay mode

This patch denies crossing the boundary of the pages in the replay mode,
because it can cause an exception. Do it only when boundary is
crossed by the first instruction in the block.
If current instruction already crossed the bound - it's ok,
because an exception hasn't stopped this code.
Signed-off-by: NPavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

target-i386/cpu.h

@@ -28,6 +28,9 @@
 #define TARGET_LONG_BITS 32
 #endif
 
+/* Maximum instruction code size */
+#define TARGET_MAX_INSN_SIZE 16
+
 /* target supports implicit self modifying code */
 #define TARGET_HAS_SMC
 /* support for self modifying code even if the modified instruction is

target-i386/translate.c

@@ -8022,6 +8022,20 @@ static inline void gen_intermediate_code_internal(X86CPU *cpu,
             gen_eob(dc);
             break;
         }
+        /* Do not cross the boundary of the pages in icount mode,
+           it can cause an exception. Do it only when boundary is
+           crossed by the first instruction in the block.
+           If current instruction already crossed the bound - it's ok,
+           because an exception hasn't stopped this code.
+         */
+        if (use_icount
+            && ((pc_ptr & TARGET_PAGE_MASK)
+                != ((pc_ptr + TARGET_MAX_INSN_SIZE - 1) & TARGET_PAGE_MASK)
+                || (pc_ptr & ~TARGET_PAGE_MASK) == 0)) {
+            gen_jmp_im(pc_ptr - dc->cs_base);
+            gen_eob(dc);
+            break;
+        }
         /* if too long translation, stop generation too */
         if (tcg_ctx.gen_opc_ptr >= gen_opc_end ||
             (pc_ptr - pc_start) >= (TARGET_PAGE_SIZE - 32) ||