// SPDX-License-Identifier: GPL-2.0-only
//
// Copyright 2024 Arm Limited
//
// Give ourselves GCS push permissions then use them

#include <asm/unistd.h>

/* Shadow Stack/Guarded Control Stack interface */
#define PR_GET_SHADOW_STACK_STATUS      74
#define PR_SET_SHADOW_STACK_STATUS      75
#define PR_LOCK_SHADOW_STACK_STATUS     76

# define PR_SHADOW_STACK_ENABLE         (1UL << 0)
# define PR_SHADOW_STACK_WRITE          (1UL << 1)
# define PR_SHADOW_STACK_PUSH           (1UL << 2)

#define KSFT_SKIP 4

.macro function name
        .macro endfunction
                .type \name, @function
                .purgem endfunction
        .endm
\name:
.endm

// Print a single character x0 to stdout
// Clobbers x0-x2,x8
function putc
        str     x0, [sp, #-16]!

        mov     x0, #1                  // STDOUT_FILENO
        mov     x1, sp
        mov     x2, #1
        mov     x8, #__NR_write
        svc     #0

        add     sp, sp, #16
        ret
endfunction
.globl  putc

// Print a NUL-terminated string starting at address x0 to stdout
// Clobbers x0-x3,x8
function puts
        mov     x1, x0

        mov     x2, #0
0:      ldrb    w3, [x0], #1
        cbz     w3, 1f
        add     x2, x2, #1
        b       0b

1:      mov     w0, #1                  // STDOUT_FILENO
        mov     x8, #__NR_write
        svc     #0

        ret
endfunction
.globl  puts

// Utility macro to print a literal string
// Clobbers x0-x4,x8
.macro puts string
        .pushsection .rodata.str1.1, "aMS", @progbits, 1
.L__puts_literal\@: .string "\string"
        .popsection

        ldr     x0, =.L__puts_literal\@
        bl      puts
.endm

.globl _start
function _start
        // Run with GCS
        mov     x0, PR_SET_SHADOW_STACK_STATUS
        mov     x1, PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_PUSH
        mov     x2, xzr
        mov     x3, xzr
        mov     x4, xzr
        mov     x5, xzr
        mov     x8, #__NR_prctl
        svc     #0
        cbz     x0, 1f
        puts    "Failed to enable GCS with push permission\n"
        mov     x0, #KSFT_SKIP
        b       2f
1:
        sys     #3, c7, c7, #0, x0      // GCSPUSHM
        sysl    x0, #3, c7, c7, #1      // GCSPOPM

        mov     x0, #0
2:
        mov     x8, #__NR_exit
        svc     #0