tcg-s390: Allocate the code_gen_buffer near the main program.

This allows the use of direct calls to the helpers,
and a direct branch back to the epilogue.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/exec.c b/exec.c
index aedfda4..4273797 100644
--- a/exec.c
+++ b/exec.c
@@ -519,6 +519,13 @@ static void code_gen_alloc(unsigned long tb_size)
         start = (void *) 0x01000000UL;
         if (code_gen_buffer_size > 16 * 1024 * 1024)
             code_gen_buffer_size = 16 * 1024 * 1024;
+#elif defined(__s390x__)
+        /* Map the buffer so that we can use direct calls and branches.  */
+        /* We have a +- 4GB range on the branches; leave some slop.  */
+        if (code_gen_buffer_size > (3ul * 1024 * 1024 * 1024)) {
+            code_gen_buffer_size = 3ul * 1024 * 1024 * 1024;
+        }
+        start = (void *)0x90000000UL;
 #endif
         code_gen_buffer = mmap(start, code_gen_buffer_size,
                                PROT_WRITE | PROT_READ | PROT_EXEC,