From 39dfe5408328043b5434c9295ac6cbdd07562957 Mon Sep 17 00:00:00 2001
From: Zakk Chen <zakk.chen@sifive.com>
Date: Tue, 10 Aug 2021 21:27:51 -0700
Subject: [PATCH] Improve nop_putc and fix bug.

in clang, the result is
c.mv         a1, a0
c.li         a0, -1
c.mv         a0, a1
slli         zero, a0, 0x11
c.jr         ra

result is incorrect, we need to add a0 into clobber list.
---
 src/tty.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/tty.c b/src/tty.c
index e5ffdb26..fff06556 100644
--- a/src/tty.c
+++ b/src/tty.c
@@ -43,7 +43,8 @@ int nop_putc(int c) {
     // truly in a0, for easier post-processing, and so there is a single
     // 32-bit opcode to match against.
     // So explicitly ensure that the argument is placed into a0 first.
-    __asm__ volatile("mv a0, %0; slli x0,a0,0x11" ::"r"(c));
+    register long xc asm("a0") = c;
+    __asm__ volatile("slli x0,a0,0x11" ::"r"(xc));
     return -1;
 }
 int metal_tty_putc(int c) __attribute__((weak, alias("nop_putc")));