work

README.md

@@ -11,6 +11,7 @@ Emulator exit codes:
 - `0` - never happens
 - `1` - invalid opcode
 - `2` - illegal instruction argument (like funct3)
+- `3` - memory error (for example writing to ROM)
 
 Compile:
 1. Dependencies: `libelf`

include/address_space.h

@@ -2,11 +2,19 @@
 #define ADDRESS_SPACE_H
 
 #include <stdint.h>
+#include <stdbool.h>
 
 struct AddressSpace_s {
+    // A pointer to a ROM array. The array can vary in length.
     uint8_t *rom;
-    uint32_t romSize;
+    // The size of ROM.
+    uint32_t romSize; // TODO look into making it const
+    // Is ROM read only
+    bool romLocked;
+
+    // A pointer to a RAM array. The array can vary in length.
     uint8_t *ram;
+    // The size of RAM.
     uint32_t ramSize;
 };
 

programs/src/segfault.c

@@ -0,0 +1,15 @@
+/**
+ * This normally causes a segfault, but won't on the emulator because it requires a strict check.
+ * The emulator emulates bare metal, where there's no such checks.
+ */
+
+int main() {
+    int *i = (int*)1;
+    *i = 10;
+
+    for (int j = 0; j < 100; j++) {
+        *(i + j) = j;
+    }
+    
+    return i;
+}

src/address_space.c

@@ -3,20 +3,7 @@
 #include <string.h>
 #include <stdlib.h>
 
-struct AddressSpace_s {
-    // A pointer to a ROM array. The array can vary in length.
-    uint8_t *rom;
-    // The size of ROM.
-    uint32_t romSize; // TODO look into making it const
-
-    // A pointer to a RAM array. The array can vary in length.
-    uint8_t *ram;
-    // The size of RAM.
-    uint32_t ramSize;
-};
-
-typedef struct AddressSpace_s AddressSpace;
-
+#include "address_space.h"
 
 AddressSpace *create_address_space(const uint32_t romSize, const uint32_t ramSize) {
     uint8_t *rom = calloc(romSize, 1);
@@ -33,6 +20,7 @@ AddressSpace *create_address_space(const uint32_t romSize, const uint32_t ramSiz
 
     addressSpace->rom = rom;
     addressSpace->romSize = romSize;
+    addressSpace->romLocked = false;
     addressSpace->ram = ram;
     addressSpace->ramSize = ramSize;
 
@@ -71,6 +59,11 @@ int write_address_space(const AddressSpace *addressSpace, const uint32_t address
     uint32_t ramSize = addressSpace->ramSize;
 
     if (address < romSize) {
+        if (addressSpace->romLocked) {
+            fprintf(stderr, "Cannot write to ROM\n");
+            return 2;
+        }
+        
         if (address + n >= romSize) {
             fprintf(stderr, "Writing %d bytes to %d will exceed ROM address space of %d\n", n, address, romSize);
             return 1;

src/cpu.c

@@ -69,8 +69,7 @@ void print_registers(CPU *cpu) {
     for (int rown=0; rown<rows; rown++) {
         printf("│ ");
         for (int coln=0; coln<columns; coln++) {
-            //printf("%d", colSize[coln]);
-            char *entry = malloc(colSize[coln]);
+            char entry[50] = {0};
             int len = snprintf(entry, colSize[coln]+1, "x%d: \033[1m0x%X\033[0m (%u)", i, registers[i], registers[i]);
             memset(entry + len, ' ', colSize[coln] - len);
 

src/elf_program_loader.c

@@ -40,6 +40,12 @@ static inline int process_elf(Elf *elf, CPU *cpu) {
         return 1;
     }
 
+    uint32_t textSize = 0;
+    uint8_t *text;
+
+    uint32_t rodataSize = 0;
+    uint8_t *rodata;
+
     while ((scn = elf_nextscn(elf, scn)) != NULL) {
         if (gelf_getshdr(scn, &shdr) != &shdr) {
             fprintf(stderr, "getshdr() failed: %s\n", elf_errmsg(-1));
@@ -73,17 +79,18 @@ static inline int process_elf(Elf *elf, CPU *cpu) {
                 continue;
             }
 
-            char *content = (char *)data->d_buf;
-            uint32_t contentSize = data->d_size;
-
-            if (contentSize > addressSpace->romSize) {
-                fprintf(stderr, "Code has %d bytes, and doesn't fit in ROM of capacity %d bytes\n", contentSize, addressSpace->romSize);
-                return 1;
+            text = (uint8_t *)data->d_buf;
+            textSize = data->d_size;
+        } else if (strcmp(sectionName, ".rodata") == 0) {
+            Elf_Data *data = elf_getdata(scn, NULL);
+            
+            if (data == NULL || data->d_size == 0) {
+                fprintf(stderr, "elf_getdata() failed: %s\n", elf_errmsg(-1));
+                continue;
             }
 
-            memcpy(addressSpace->rom, content, contentSize);
-
-            printf("Loaded %d bytes or %d instructions from an ELF file\n", contentSize, contentSize / 4);
+            rodata = (uint8_t *)data->d_buf;
+            rodataSize = data->d_size;
         } else {
             printf("Unrecognized section: %s\n", sectionName);
         }
@@ -93,6 +100,30 @@ static inline int process_elf(Elf *elf, CPU *cpu) {
         printf("I couldn't verify whether the ELF was compiled for the correct instruction set!\n");
     }
 
+    if (textSize > 0) {
+        if (textSize > addressSpace->romSize) {
+            fprintf(stderr, "Code has %d bytes, and doesn't fit in ROM of capacity %d bytes\n", textSize, addressSpace->romSize);
+            return 1;
+        }
+
+        memcpy(addressSpace->rom, text, textSize);
+    } else {
+        fprintf(stderr, "There's no code\n");
+        return 1;
+    }
+
+    if (rodataSize > 0) {
+        uint32_t totalSize = rodataSize + textSize;
+        if (totalSize > addressSpace->romSize) {
+            fprintf(stderr, "Code %d + rodata %d = %d bytes, which doesn't fit in ROM of capacity %d bytes\n", textSize, rodataSize, totalSize, addressSpace->romSize);
+            return 1;
+        }
+
+        memcpy(addressSpace->rom + textSize, rodata, rodataSize);
+    }
+
+    printf("Loaded from ELF | Code: %d bytes (%d insts) | ROdata: %d bytes \n", textSize, textSize / 4, rodataSize);
+
     cpu->programCounter = ehdr.e_entry;
 
     return 0;

src/instruction_executor.c

@@ -2,7 +2,7 @@
 #include <stdio.h>
 #include <stdbool.h>
 
-#define VERBOSE_LOGGING 0
+#define VERBOSE_LOGGING 1
 
 static void printBinary(uint32_t num) {
     if (num > 1) {
@@ -40,8 +40,8 @@ int execute_instruction_on_cpu(CPU *cpu, uint32_t instruction) { // TODO conside
 
             int32_t imm = ((int32_t)instruction >> 31) << 12; // imm[12] and sign extension
             imm |= ((instruction >> 7) & 0x1) << 11;  // imm[11]
-            imm |= ((instruction >> 25) & 0x3f) << 5; // imm[10:5]
-            imm |= ((instruction >> 8) & 0xf) << 1;   // imm[4:1]
+            imm |= ((instruction >> 25) & 0x3F) << 5; // imm[10:5]
+            imm |= ((instruction >> 8) & 0xF) << 1;   // imm[4:1]
             // imm[0] is implicitly 0
 
             bool branch = false;
@@ -69,10 +69,10 @@ int execute_instruction_on_cpu(CPU *cpu, uint32_t instruction) { // TODO conside
             }
 
             if (branch) {
-                printf(" Yes, branching");
+                printf(" Yes, branching by 0x%X to 0x%X", imm, cpu->programCounter + imm);
                 cpu->programCounter += imm - 4; // program counter is always incremented after executing instruction so -4
             } else {
-                printf(" No, not branching");
+                printf(" No, not branching by 0x%X to 0x%X", imm, cpu->programCounter + imm);
             }
             break;
         }
@@ -82,15 +82,29 @@ int execute_instruction_on_cpu(CPU *cpu, uint32_t instruction) { // TODO conside
             int32_t imm = (int32_t)instruction >> 20;
 
             switch (funct3) {
-                case 0b000: // ADDI
-                    printf("ADDI - x%u 0x%X (%d) + 0x%X (%d) = 0x%X -> x%u", rs1, registers[rs1], registers[rs1], imm, imm, registers[rs1] + imm, rd);
+                case 0b000: {
+                    // ADDI
+                    printf("ADDI: x%u 0x%X (%d) + 0x%X (%d) = 0x%X -> x%u", rs1, registers[rs1], registers[rs1], imm, imm, registers[rs1] + imm, rd);
                     registers[rd] = registers[rs1] + imm;
                     break;
-                default:
+                }
+                case 0b001: { // SLLI
+                    uint8_t shamt = imm & 0x1F;
+                    imm = imm >> 5 & 0x3F;
+                    if (imm != 0b0000000) {
+                        fprintf(stderr, "Invalid SLLI imm[11:5], must be zero but is 0x%X", (imm >> 5 & 0x3F));
+                        return 2;
+                    }
+                    printf("SLLI: x%u 0x%X (%d) << %d = 0x%X -> x%u", rs1, registers[rs1], registers[rs1], imm, registers[rs1] << shamt, rd);
+                    registers[rd] = registers[rs1] << shamt;
+                    break;
+                }
+                default: {
                     // TODO proper error handling
                     fprintf(stderr, "Invalid OP-IMM funct3: 0x%X", funct3);
                     return 2;
                     break;
+                }
             }
             /* code */
             break;
@@ -119,11 +133,11 @@ int execute_instruction_on_cpu(CPU *cpu, uint32_t instruction) { // TODO conside
             registers[rd] = cpu->programCounter + 4;
             cpu->programCounter = result - 4; // program counter is always incremented after executing instruction
 
-            printf("JALR - x%u %u + %u = %u", rs1, result - imm, imm, result);
+            printf("JALR - x%u %u + %u = 0x%X", rs1, result - imm, imm, result);
 
             break;
         }
-        case 0b0100011: { // STORE instruction (S type)
+        case 0b0100011: { // STORE instruction (S type), write errors are ignored
             uint8_t funct3 = instruction >> 12 & 0x7;
             uint8_t rs1 = instruction >> 15 & 0x1F;
             uint8_t rs2 = instruction >> 20 & 0x1F;
@@ -152,6 +166,7 @@ int execute_instruction_on_cpu(CPU *cpu, uint32_t instruction) { // TODO conside
                 fprintf(stderr, "Invalid STORE funct3: 0x%X", funct3);
                 return 2;
             }
+
             break;
         }
         case 0b0000011: { // LOAD instruction (I type)
@@ -218,7 +233,7 @@ int execute_instruction_on_cpu(CPU *cpu, uint32_t instruction) { // TODO conside
             registers[rd] = cpu->programCounter; // program counter is always incremented after executing instruction
             cpu->programCounter += imm;
 
-            printf("JAL: Jumped to %u + %d = %u (inst %d)", registers[rd], imm, cpu->programCounter, cpu->programCounter / 4);
+            printf("JAL: Jumped to %u + %d = 0x%X (inst %d)", registers[rd], imm, cpu->programCounter, cpu->programCounter / 4);
             break;
         }
         case 0b0110011: { // OP for Integer Register-Register Operations (R type)

src/main.c

@@ -14,7 +14,7 @@ int main(int argc, char *argv[]) {
         return 1;
     }
 
-    AddressSpace *addressSpace = create_address_space(256, 256);
+    AddressSpace *addressSpace = create_address_space(512, 512);
     printf("Address space: %dB ROM, %dB RAM\n", addressSpace->romSize, addressSpace->ramSize);
 
     CPU cpu = create_cpu(addressSpace);
@@ -31,6 +31,8 @@ int main(int argc, char *argv[]) {
         return 1;
     }
 
+    addressSpace->romLocked = true;
+
 
     printf("\n----- Start of program (0x%X) -----", cpu.programCounter);
 
@@ -47,6 +49,7 @@ int main(int argc, char *argv[]) {
     printf("  Program exit code: \033[1m%d\033[0m (x10)\n", cpu.registers[10]);
     printf("  Cycles: \033[1m%u\033[0m\n\n", cycles);
 
+    cpu.registers[0] = 0; // if x0 is changed in the last instruction (it usually is) it will be displayed what if was set to
     print_registers(&cpu);
 
     return 0;