PS1 Crash Handler

error.c

/**
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In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
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**/
/**

PS1 Crash Handler

Requirements: Generally, be using the built-in ROM routines and exception
handling. This uses the A(0x4E) call, the task control block at 0x108, and the
default exception handler that fills in the task info, and it hooks the A(0x40)
"unresolved exception" call. If you want to catch program exits, your _exit
routine should cause an exception, with e.g. the "break" instruction. Newlib
libc does this in crt0.S.

To use: Call InstallExceptionHandler to install the hook. Optionally call
PSXPrintError with an error description right before an intentional crash occurs
to add the error description to the crash display.

- Spencer Alves (impiaaa)

**/

static inline void syscall_gpu_sync(void) {
    register volatile int n asm("t1") = 0x4E;
    __asm__ volatile("" : "=r"(n) : "r"(n));
    ((void(*)(void))0xA0)();
}

static volatile unsigned int* GP0 = (volatile unsigned int*)0xBF801810;
static volatile unsigned int* GP1 = (volatile unsigned int*)0xBF801814;

static int charX = 0;
static int charY = 0;
static const int charWidth = 8;
static const int charHeight = 15;
static const int screenWidth = 320;
typedef int bool;
#define false 0
#define true 1
static bool hasDarkenedScreen = false;

static void DarkenScreen() {
    *GP1 = 0x01000000; // clear command buffer
    *GP1 = 0x04000000; // disable DMA
    *GP1 = 0x08000001|((((*GP1)&0x100000) != 0)<<3); // 320x240, no interlace, 15bpp, preserve video mode
    syscall_gpu_sync();
    *GP0 = 0xE1000400; // 50/50 blend mode, texture don't care, drawing allowed
    syscall_gpu_sync();
    *GP0 = 0xE3000000; // drawing area top-left 0,0
    syscall_gpu_sync();
    *GP0 = 0xE4000000|(256<<10)|(screenWidth); // drawing area bottom-right
    syscall_gpu_sync();
    *GP0 = 0xE5000000; // drawing offset top-left
    syscall_gpu_sync();
    *GP0 = 0xE6000000; // disable masking
    syscall_gpu_sync();
    *GP0 = 0x63000000; // black, semitransparent rectangle
    *GP0 = 0x00000000; // top-left
    *GP0 = (256<<16)|(screenWidth); // full screen
}

static void PrintCharacter(const char c) {
    if (c == '\b') {
        charX -= charWidth;
        if (charX < 0) {
            charX = screenWidth-8;
            charY -= charHeight;
        }
    }
    else if (c == '\n') {
        charX = 0;
        charY += charHeight;
    }
    else if (c == '\r') {
        charX = 0;
    }
    else {
        if (c == '\t') {
            charX = (charX+charWidth)&0xFFE0;
        }
        else if (c == ' ') {
            charX += charWidth;
        }
        else if (c >= 0x21 && c <= 0x7E) {
            for (int row = 0; row < charHeight; row++) {
                unsigned int bits = *(unsigned char *)(0xBFC7F8DE + charHeight*(c - 0x21) + row);
                for (int col = charWidth-1; col >= 0 && bits != 0; col--) {
                    if (bits&1) {
                        syscall_gpu_sync();
                        *GP0 = 0x69FFFFFF; // white pixel
                        *GP0 = ((charY+row)<<16)|(charX+col);
                    }
                    bits >>= 1;
                }
            }
            charX += charWidth;
        }
        else {
            return;
        }
        if (charX >= screenWidth) {
            charX = 0;
            charY += charHeight;
        }
    }
}

static void PrintHex(unsigned x) {
    for (int i = 0; i < 8; i++) {
        int c = x>>28;
        PrintCharacter(c > 9 ? c-10+'A' : c+'0');
        x <<= 4;
    }
}

// Public API: Call this before right calling abort(), exit() etc. to add a
// message to the screen before the crash info
void PSXPrintError(const char* s) {
    if (!hasDarkenedScreen) {
        hasDarkenedScreen = true;
        DarkenScreen();
    }
    if (s == (const char*)0) return;
    while (*s) {
        PrintCharacter(*s);
        s++;
    }
}

struct TCBH {
	struct TCB *entry;
	long flag;
};

struct TCB {
	long status;
	long mode;
	unsigned long reg[40];
	long system[6];
};

static const struct TCBH** taskControlBlockHeaderPointer = (struct TCBH**)0x108;

static void (* oldHandler)();

static void UnresolvedException() {
    // BIOS exception handler clobbers $gp; restore it
    asm("la $gp, _gp");
    
    // if the exception came from _exit, a0 has the passed exit code
    struct TCB* task = (*taskControlBlockHeaderPointer)->entry;
    PSXPrintError("code=");
    PrintHex(task->reg[4]);
    
    // cop0r13/cause at the time of the exception
    PSXPrintError(" cause=");
    PrintHex(task->reg[36]);
    
    // cop0r14/epc at the time of the exception
    PSXPrintError(" pc=");
    PrintHex(task->reg[32]);
    
    //PrintCharacter('\n'); // above is 40 characters
    
    // dump stack
    unsigned* sp = (unsigned *)task->reg[29];
    while ((((unsigned)sp)&(~0xE0000000)) >= 0 && (((unsigned)sp)&(~0xE0000000)) < 0x200000 && charY < 256) {
        PrintHex(*sp);
        PrintCharacter(' ');
        PrintCharacter(' ');
        sp++;
    }
    
    // ensure display
    syscall_gpu_sync();
    *GP1 = 0x05000000; // top-left corner
    *GP1 = 0x03000000; // enable display
    
    // continue to the existing handler
    // by default it calls the same handler, which since we've redirected that
    // here, could overflow the stack. a debugger could still hook the same
    // function though and we'd like to fall through, so check for the default implementation
    if (((unsigned *)oldHandler)[0] != 0x240A00A0 ||
        ((unsigned *)oldHandler)[1] != 0x01400008 ||
        ((unsigned *)oldHandler)[2] != 0x24090040) {
        oldHandler();
    }
    // if it was the default implementation, or it returned control, hang
    while(1) {
        // some emulators only refresh the display if the GPU is poked
        volatile int foo = *GP1;
    }
}

static void (** const a0table)() = (void (**)())0x200;

// Public API: Call this to start catching crashes
void InstallExceptionHandler() {
    oldHandler = a0table[0x40];
    a0table[0x40] = UnresolvedException;
}