[PATCH 2/2] RISC-V: Add _LITE_EXIT in crt0.S.

This patch adds _LITE_EXIT in crt0.S to enable "lite exit" technique in 
RISC-V. The changes have been tested in riscv/riscv-gnu-toolchain by 
riscv-dejagnu with riscv-sim.exp/riscv-sim-nano.exp.

 From d51d7c69a2c60041ef583686f24ccae74b675edc Mon Sep 17 00:00:00 2001
 From: Ilia Diachkov <[email protected]>
Date: Sat, 18 May 2019 02:08:36 +0300
Subject: [PATCH 2/2] RISC-V: Add _LITE_EXIT in crt0.S.

---
  libgloss/riscv/crt0.S | 11 +++++++++++
  1 file changed, 11 insertions(+)

diff --git a/libgloss/riscv/crt0.S b/libgloss/riscv/crt0.S
index 3d2a12d..7e1c025 100644
--- a/libgloss/riscv/crt0.S
+++ b/libgloss/riscv/crt0.S
@@ -9,6 +9,8 @@
     http://www.opensource.org/licenses.
  */

+#include "newlib.h"
+
  
#=========================================================================
  # crt0.S : Entry point for RISC-V user programs
  
#=========================================================================
@@ -30,9 +32,18 @@ _start:
    sub     a2, a2, a0
    li      a1, 0
    call    memset
+#ifdef _LITE_EXIT
+  # Make reference to atexit weak to avoid unconditionally pulling in
+  # support code.  Refer to comments in __atexit.c for more details.
+  .weak   atexit
+  la      a0, atexit
+  beqz    a0, .Lweak_atexit
+  .weak   __libc_fini_array
+#endif

    la      a0, __libc_fini_array   # Register global termination 
functions
    call    atexit                  #  to be called upon exit
+.Lweak_atexit:
    call    __libc_init_array       # Run global initialization functions

    lw      a0, 0(sp)                  # a0 = argc
-- 
1.8.3.1