1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
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
|
