--- /dev/null
+/* 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
+ la gp, __global_pointer$
+.option pop
+
+ /* Set up a simple trap vector to catch anything that goes wrong early in
+ * the boot process. */
+ la t0, early_trap_vector
+ csrw mtvec, t0
+ /* enable chicken bit if core is bullet series*/
+ la t0, __metal_chicken_bit
+ beqz t0, 1f
+ csrwi 0x7C1, 0
+1:
+
+ /* There may be pre-initialization routines inside the MBI code that run in
+ * C, so here we set up a C environment. First we set up a stack pointer,
+ * which is left as a weak reference in order to allow initialization
+ * routines that do not need a stack to be set up to transparently be
+ * called. */
+ .weak __metal_stack_pointer
+ la sp, __metal_stack_pointer
+
+ /* Check for an initialization routine and call it if one exists, otherwise
+ * just skip over the call entirely. Note that __metal_initialize isn't
+ * actually a full C function, as it doesn't end up with the .bss or .data
+ * segments having been initialized. This is done to avoid putting a
+ * burden on systems that can be initialized without having a C environment
+ * set up. */
+ .weak __metal_before_start
+ la ra, __metal_before_start
+ beqz ra, 1f
+ jalr ra
+1:
+
+ /* At this point we can enter the C runtime's startup file. The arguments
+ * to this function are designed to match those provided to the SEE, just
+ * so we don't have to write another ABI. */
+ csrr a0, mhartid
+ li a1, 0
+ li a2, 0
+ call _start
+
+ /* If we've made it back here then there's probably something wrong. We
+ * allow the METAL to register a handler here. */
+ .weak __metal_after_main
+ la ra, __metal_after_main
+ beqz ra, 1f
+ jalr ra
+1:
+
+ /* If that handler returns then 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
+
+/* For sanity's sake we set up an early trap vector that just does nothing. If
+ * you end up here then there's a bug in the early boot code somewhere. */
+.section .text.metal.init.trapvec
+.align 2
+early_trap_vector:
+ .cfi_startproc
+ csrr t0, mcause
+ csrr t1, mepc
+ csrr t2, mtval
+ j early_trap_vector
+ .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
projects / freertos / blobdiff