tcg: Add in_code_gen_buffer

Create a function to determine if a pointer is within the buffer.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/translate-all.c

@@ -392,27 +392,18 @@ void tb_destroy(TranslationBlock *tb)
 
 bool cpu_restore_state(CPUState *cpu, uintptr_t host_pc, bool will_exit)
 {
-    TranslationBlock *tb;
-    bool r = false;
-    uintptr_t check_offset;
-
-    /* The host_pc has to be in the region of current code buffer. If
-     * it is not we will not be able to resolve it here. The two cases
-     * where host_pc will not be correct are:
+    /*
+     * The host_pc has to be in the region of the code buffer.
+     * If it is not we will not be able to resolve it here.
+     * The two cases where host_pc will not be correct are:
      *
      *  - fault during translation (instruction fetch)
      *  - fault from helper (not using GETPC() macro)
      *
      * Either way we need return early as we can't resolve it here.
-     *
-     * We are using unsigned arithmetic so if host_pc <
-     * tcg_init_ctx.code_gen_buffer check_offset will wrap to way
-     * above the code_gen_buffer_size
      */
-    check_offset = host_pc - (uintptr_t) tcg_init_ctx.code_gen_buffer;
-
-    if (check_offset < tcg_init_ctx.code_gen_buffer_size) {
-        tb = tcg_tb_lookup(host_pc);
+    if (in_code_gen_buffer((const void *)host_pc)) {
+        TranslationBlock *tb = tcg_tb_lookup(host_pc);
         if (tb) {
             cpu_restore_state_from_tb(cpu, tb, host_pc, will_exit);
             if (tb_cflags(tb) & CF_NOCACHE) {
@@ -421,11 +412,10 @@ bool cpu_restore_state(CPUState *cpu, uintptr_t host_pc, bool will_exit)
                 tcg_tb_remove(tb);
                 tb_destroy(tb);
             }
-            r = true;
+            return true;
         }
     }
-
-    return r;
+    return false;
 }
 
 static void page_init(void)

include/tcg/tcg.h

@@ -680,6 +680,17 @@ extern __thread TCGContext *tcg_ctx;
 extern void *tcg_code_gen_epilogue;
 extern TCGv_env cpu_env;
 
+static inline bool in_code_gen_buffer(const void *p)
+{
+    const TCGContext *s = &tcg_init_ctx;
+    /*
+     * Much like it is valid to have a pointer to the byte past the
+     * end of an array (so long as you don't dereference it), allow
+     * a pointer to the byte past the end of the code gen buffer.
+     */
+    return (size_t)(p - s->code_gen_buffer) <= s->code_gen_buffer_size;
+}
+
 static inline size_t temp_idx(TCGTemp *ts)
 {
     ptrdiff_t n = ts - tcg_ctx->temps;