From 2c4e689bc1ed4440d0d95b3b350ce872e7f75865 Mon Sep 17 00:00:00 2001
From: James Clarke <jrtc27@jrtc27.com>
Date: Mon, 3 Feb 2020 00:53:17 +0000
Subject: Support manually zeroing out BSS when booting (#188)

Some ELF loaders, in particular gdb's load command for dynamically
loading files into memory, which is often used to load binaries onto
FPGAs over JTAG, do not zero out BSS, leaving the memory in whatever
state it was previously in. Thus, introduce a new --enable-zero-bss
configure flag, which will include code to zero out BSS when booting.
---
 machine/mentry.S | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

(limited to 'machine')

diff --git a/machine/mentry.S b/machine/mentry.S
index 84bd3c1..9ec9916 100644
--- a/machine/mentry.S
+++ b/machine/mentry.S
@@ -267,9 +267,23 @@ do_reset:
   slli a2, a3, RISCV_PGSHIFT
   add sp, sp, a2
 
+  bnez a3, .LmultiHartInit
+
+#ifdef ZERO_BSS
+  # Zero out BSS; linker script provides alignment and padding
+  la t0, _fbss
+  la t1, _end
+  beq t0, t1, 2f
+1:STORE zero, 0(t0)
+  addi t0, t0, REGBYTES
+  bne t0, t1, 1b
+2:
+#endif
+
   # Boot on the first hart
-  beqz a3, init_first_hart
+  j init_first_hart
 
+.LmultiHartInit:
   # set MSIE bit to receive IPI
   li a2, MIP_MSIP
   csrw mie, a2
-- 
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