From 15419dae8386c976b3b93493c7b01f169423ba58 Mon Sep 17 00:00:00 2001
From: Uros Majstorovic <majstor@majstor.org>
Date: Sun, 4 Sep 2022 18:07:29 +0200
Subject: init routines cleanup

---
 fw/fe310/bsp/init/entry.S | 63 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 fw/fe310/bsp/init/entry.S

(limited to 'fw/fe310/bsp/init/entry.S')

diff --git a/fw/fe310/bsp/init/entry.S b/fw/fe310/bsp/init/entry.S
new file mode 100644
index 0000000..6b80217
--- /dev/null
+++ b/fw/fe310/bsp/init/entry.S
@@ -0,0 +1,63 @@
+/* Copyright 2018 SiFive, Inc */
+/* SPDX-License-Identifier: Apache-2.0 */
+
+/* This code executes before _start, which is contained inside the C library.
+ * In embedded systems we want to ensure that _enter, which contains the first
+ * code to be executed, can be loaded at a specific address.  To enable this
+ * feature we provide the '.text.metal.init.enter' section, which is
+ * defined to have the first address being where execution should start. */
+.section .text.metal.init.enter
+.global _enter
+_enter:
+  .cfi_startproc
+
+ /* Inform the debugger that there is nowhere to backtrace past _enter. */
+  .cfi_undefined ra
+
+ /* The absolute first thing that must happen is configuring the global
+  * pointer register, which must be done with relaxation disabled because
+  * it's not valid to obtain the address of any symbol without GP
+  * configured. The C environment might go ahead and do this again, but
+  * that's safe as it's a fixed register. */
+.option push
+.option norelax
+1:auipc gp, %pcrel_hi(__global_pointer$)
+  addi  gp, gp, %pcrel_lo(1b)
+.option pop
+
+ /* Set up a trap vector */
+  la t0, eos_trap_vector
+  csrw mtvec, t0
+
+ /* This is a bare-metal environment and therefor is expected
+  * to define its own stack pointer.  We also align the stack pointer here
+  * because the only RISC-V ABI that's currently defined mandates 16-byte
+  * stack alignment. */
+  la sp, _sp
+  andi sp, sp, -16
+
+ /* At this point we can enter the C runtime's startup file. */
+  call _start
+
+ /* If we've made it back here then there's probably something wrong.
+  * There's not a whole lot we can do, just try to make some noise. */
+  la t0, 1f
+  csrw mtvec, t0
+1:
+  lw t1, 0(x0)
+  j 1b
+
+  .cfi_endproc
+
+/* The GCC port might not emit a __register_frame_info symbol, which eventually
+ * results in a weak undefined reference that eventually causes crash when it
+ * is dereference early in boot.  We really shouldn't need to put this here,
+ * but to deal with what I think is probably a bug in the linker script I'm
+ * going to leave this in for now.  At least it's fairly cheap :) */
+.weak __register_frame_info
+.global __register_frame_info
+.section .text.metal.init.__register_frame_info
+__register_frame_info:
+  .cfi_startproc
+  ret
+  .cfi_endproc
-- 
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