tcg: Emit prologue to the beginning of code_gen_buffer

By putting the prologue at the end, we risk overwriting the
prologue should our estimate of maximum TB size.  Given the
two different placements of the call to tcg_prologue_init,
move the high water mark computation into tcg_prologue_init.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>

1 files changed, 28 insertions, 7 deletions

diff --git a/tcg/tcg.c b/tcg/tcg.c
index d3693b17f2..56091087a4 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -363,17 +363,38 @@ void tcg_context_init(TCGContext *s)
 
 void tcg_prologue_init(TCGContext *s)
 {
-    /* init global prologue and epilogue */
-    s->code_buf = s->code_gen_prologue;
-    s->code_ptr = s->code_buf;
+    size_t prologue_size, total_size;
+    void *buf0, *buf1;
+
+    /* Put the prologue at the beginning of code_gen_buffer.  */
+    buf0 = s->code_gen_buffer;
+    s->code_ptr = buf0;
+    s->code_buf = buf0;
+    s->code_gen_prologue = buf0;
+
+    /* Generate the prologue.  */
     tcg_target_qemu_prologue(s);
-    flush_icache_range((uintptr_t)s->code_buf, (uintptr_t)s->code_ptr);
+    buf1 = s->code_ptr;
+    flush_icache_range((uintptr_t)buf0, (uintptr_t)buf1);
+
+    /* Deduct the prologue from the buffer.  */
+    prologue_size = tcg_current_code_size(s);
+    s->code_gen_ptr = buf1;
+    s->code_gen_buffer = buf1;
+    s->code_buf = buf1;
+    total_size = s->code_gen_buffer_size - prologue_size;
+    s->code_gen_buffer_size = total_size;
+
+    /* Compute a high-water mark, at which we voluntarily flush the
+       buffer and start over.  */
+    s->code_gen_buffer_max_size = total_size - TCG_MAX_OP_SIZE * OPC_BUF_SIZE;
+
+    tcg_register_jit(s->code_gen_buffer, total_size);
 
 #ifdef DEBUG_DISAS
     if (qemu_loglevel_mask(CPU_LOG_TB_OUT_ASM)) {
-        size_t size = tcg_current_code_size(s);
-        qemu_log("PROLOGUE: [size=%zu]\n", size);
-        log_disas(s->code_buf, size);
+        qemu_log("PROLOGUE: [size=%zu]\n", prologue_size);
+        log_disas(buf0, prologue_size);
         qemu_log("\n");
         qemu_log_flush();
     }