On 2015-09-30 15:09, Richard Henderson wrote:
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 <address@hidden>
Signed-off-by: Richard Henderson <address@hidden>
---
tcg/tcg.c | 35 ++++++++++++++++++++++++++++-------
translate-all.c | 28 +++++++++-------------------
2 files changed, 37 insertions(+), 26 deletions(-)
Good idea to move it. I have done some experiments with putting slow
path "helpers" in the prologue, and I ended-up going over the 1024
bytes limits.
diff --git a/tcg/tcg.c b/tcg/tcg.c
index d3693b1..5609108 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);
I am not sure why you moved this 2 lines there, I think they have more
their place in code_gen_alloc() so that the heuristics stay at the same
place. total_size is available in s->code_gen_buffer_size, so that
should be doable.