| /* 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 |
