// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>

typedef unsigned int instr;

#define MAJOR_OP        0xfc000000
#define LDA_OP          0x20000000
#define STQ_OP          0xb4000000
#define BR_OP           0xc0000000

#define STK_ALLOC_1     0x23de8000 /* lda $30,-X($30) */
#define STK_ALLOC_1M    0xffff8000
#define STK_ALLOC_2     0x43c0153e /* subq $30,X,$30 */
#define STK_ALLOC_2M    0xffe01fff

#define MEM_REG         0x03e00000
#define MEM_BASE        0x001f0000
#define MEM_OFF         0x0000ffff
#define MEM_OFF_SIGN    0x00008000
#define BASE_SP         0x001e0000

#define STK_ALLOC_MATCH(INSTR)                  \
  (((INSTR) & STK_ALLOC_1M) == STK_ALLOC_1      \
   || ((INSTR) & STK_ALLOC_2M) == STK_ALLOC_2)
#define STK_PUSH_MATCH(INSTR) \
  (((INSTR) & (MAJOR_OP | MEM_BASE | MEM_OFF_SIGN)) == (STQ_OP | BASE_SP))
#define MEM_OP_OFFSET(INSTR) \
  (((long)((INSTR) & MEM_OFF) << 48) >> 48)
#define MEM_OP_REG(INSTR) \
  (((INSTR) & MEM_REG) >> 22)

/* Branches, jumps, PAL calls, and illegal opcodes end a basic block. */
#define BB_END(INSTR)                                           \
  (((instr)(INSTR) >= BR_OP) | ((instr)(INSTR) < LDA_OP) |      \
   ((((instr)(INSTR) ^ 0x60000000) < 0x20000000) &              \
    (((instr)(INSTR) & 0x0c000000) != 0)))

#define IS_KERNEL_TEXT(PC) ((unsigned long)(PC) > START_ADDR)

static char reg_name[][4] = {
        "v0 ", "t0 ", "t1 ", "t2 ", "t3 ", "t4 ", "t5 ", "t6 ", "t7 ",
        "s0 ", "s1 ", "s2 ", "s3 ", "s4 ", "s5 ", "s6 ", "a0 ", "a1 ",
        "a2 ", "a3 ", "a4 ", "a5 ", "t8 ", "t9 ", "t10", "t11", "ra ",
        "pv ", "at ", "gp ", "sp ", "0"
};


static instr *
display_stored_regs(instr * pro_pc, unsigned char * sp)
{
        instr * ret_pc = 0;
        int reg;
        unsigned long value;

        printk("Prologue [<%p>], Frame %p:\n", pro_pc, sp);
        while (!BB_END(*pro_pc))
                if (STK_PUSH_MATCH(*pro_pc)) {
                        reg = (*pro_pc & MEM_REG) >> 21;
                        value = *(unsigned long *)(sp + (*pro_pc & MEM_OFF));
                        if (reg == 26)
                                ret_pc = (instr *)value;
                        printk("\t\t%s / 0x%016lx\n", reg_name[reg], value);
                }
        return ret_pc;
}

static instr *
seek_prologue(instr * pc)
{
        while (!STK_ALLOC_MATCH(*pc))
                --pc;
        while (!BB_END(*(pc - 1)))
                --pc;
        return pc;
}

static long
stack_increment(instr * prologue_pc)
{
        while (!STK_ALLOC_MATCH(*prologue_pc))
                ++prologue_pc;

        /* Count the bytes allocated. */
        if ((*prologue_pc & STK_ALLOC_1M) == STK_ALLOC_1M)
                return -(((long)(*prologue_pc) << 48) >> 48);
        else
                return (*prologue_pc >> 13) & 0xff;
}

void
stacktrace(void)
{
        instr * ret_pc;
        instr * prologue = (instr *)stacktrace;
        unsigned char *sp = (unsigned char *)current_stack_pointer;

        printk("\tstack trace:\n");
        do {
                ret_pc = display_stored_regs(prologue, sp);
                sp += stack_increment(prologue);
                prologue = seek_prologue(ret_pc);
        } while (IS_KERNEL_TEXT(ret_pc));
}