copy the rest of the logic

.clangd

@@ -0,0 +1,4 @@
+If:
+  Language: c++
+CompileFlags:
+  Add: [-std=c++20]

build.sh

@@ -17,7 +17,7 @@ if command -v pkg-config >/dev/null; then
     LIBELF_FLAGS=$(pkg-config --cflags --libs libelf 2>/dev/null)
     if [ $? -eq 0 ]; then
         echo "building riscv64..."
-        c++ $COMMON -o riscv64 riscv64.cc $LIBELF_FLAGS
+        c++ -std=c++20 $COMMON -o riscv64 riscv64.cc $LIBELF_FLAGS
     else
         echo "libelf not found - skipping riscv64..."
     fi

riscv64.cc

@@ -1,7 +1,9 @@
 // https://docs.riscv.org/reference/isa/unpriv/rv-32-64g.html
 // https://riscv.org/wp-content/uploads/2024/12/riscv-calling.pdf
 
+#include <algorithm>
 #include <array>
+#include <bit>
 #include <cstring>
 #include <fstream>
 #include <gelf.h>
@@ -9,6 +11,55 @@
 #include <libelf.h>
 #include <vector>
 
+// TODO: dont use macros now that we're in an actual language
+#define PARSE_I_INS(ins)                                                       \
+  u8 rd = (ins >> 7) & 0b11111;                                                \
+  u8 funct3 = (ins >> 12) & 0b111;                                             \
+  u8 rs1 = (ins >> 15) & 0b11111;                                              \
+  i32 imm = ((i32)ins) >> 20
+
+#define PARSE_R_INS(ins)                                                       \
+  u8 rd = (ins >> 7) & 0b11111;                                                \
+  u8 funct3 = (ins >> 12) & 0b111;                                             \
+  u8 rs1 = (ins >> 15) & 0b11111;                                              \
+  u8 rs2 = (ins >> 20) & 0b11111;                                              \
+  i32 funct7 = ((i32)ins) >> 25
+
+#define PARSE_B_INS(ins)                                                       \
+  u8 funct3 = (ins >> 12) & 0b111;                                             \
+  u8 rs1 = (ins >> 15) & 0b11111;                                              \
+  u8 rs2 = (ins >> 20) & 0b11111;                                              \
+  i32 imm_12 = (ins >> 31) & 0b1;                                              \
+  i32 imm_10_5 = (ins >> 25) & 0b111111;                                       \
+  i32 imm_4_1 = (ins >> 8) & 0b1111;                                           \
+  i32 imm_11 = (ins >> 7) & 0b1;                                               \
+  i32 imm =                                                                    \
+      (imm_12 << 12) | (imm_11 << 11) | (imm_10_5 << 5) | (imm_4_1 << 1);      \
+  imm = (imm << 19) >> 19
+
+#define PARSE_S_INS(ins)                                                       \
+  u8 funct3 = (ins >> 12) & 0b111;                                             \
+  u8 rs1 = (ins >> 15) & 0b11111;                                              \
+  u8 rs2 = (ins >> 20) & 0b11111;                                              \
+  i32 imm_11_5 = (ins >> 25) & 0b1111111;                                      \
+  i32 imm_4_0 = (ins >> 7) & 0b11111;                                          \
+  i32 imm = (imm_11_5 << 5) | imm_4_0;                                         \
+  imm = (imm << 20) >> 20
+
+#define PARSE_J_INS(ins)                                                       \
+  u8 rd = (ins >> 7) & 0b11111;                                                \
+  i32 imm_20 = (ins >> 31) & 0b1;                                              \
+  i32 imm_10_1 = (ins >> 21) & 0b1111111111;                                   \
+  i32 imm_11 = (ins >> 20) & 0b1;                                              \
+  i32 imm_19_12 = (ins >> 12) & 0b11111111;                                    \
+  i32 imm =                                                                    \
+      (imm_20 << 20) | (imm_19_12 << 12) | (imm_11 << 11) | (imm_10_1 << 1);   \
+  imm = (imm << 11) >> 11
+
+#define PARSE_U_INS(ins)                                                       \
+  u8 rd = (ins >> 7) & 0b11111;                                                \
+  i32 imm = ins >> 12
+
 using i8 = int8_t;
 using i16 = int16_t;
 using i32 = int32_t;
@@ -17,7 +68,9 @@ using u8 = uint8_t;
 using u16 = uint16_t;
 using u32 = uint32_t;
 using u64 = uint64_t;
-static_assert(sizeof(size_t) == sizeof(u64), "size_t must be 64-bit");
+static_assert(sizeof(size_t) == sizeof(u64), "u64 must be 64-bit");
+static_assert(std::endian::native == std::endian::little,
+              "Big endianness not supported");
 
 static constexpr u64 MEMORY_SIZE = 20 * 1024 * 1024; // should be enough
 
@@ -47,17 +100,770 @@ public:
       GElf_Phdr phdr;
       gelf_getphdr(elf, i, &phdr);
       if (phdr.p_type == PT_LOAD) {
-        memcpy(m_memory.data() + phdr.p_vaddr, exe_bytes.data() + phdr.p_offset,
+        std::copy_n(exe_bytes.data() + phdr.p_offset, phdr.p_filesz,
-               phdr.p_filesz);
+                    m_memory.data() + phdr.p_vaddr);
       }
     }
     elf_end(elf);
   }
 
+  void disassemble_all() {
+    for (m_pc = m_code_section.offset;
+         m_pc < m_code_section.offset + m_code_section.size; m_pc += 4) {
+      disassemble_one();
+    }
+  }
+
+  void disassemble_one() {
+    u32 ins;
+    std::memcpy(&ins, m_memory.data() + m_pc, sizeof(ins));
+
+    u16 opcode = ins & 0b1111111;
+
+    // https://stackoverflow.com/questions/62939410/how-can-i-find-out-the-instruction-format-of-a-risc-v-instruction
+    switch (opcode) {
+    case 0b1100011: {
+      PARSE_B_INS(ins);
+
+      if (funct3 == 0b000) {
+        printf("beq %s, %s, %d\n", REGS[rs1], REGS[rs2], imm);
+      } else if (funct3 == 0b001) {
+        printf("bne %s, %s, %d\n", REGS[rs1], REGS[rs2], imm);
+      } else if (funct3 == 0b100) {
+        printf("blt %s, %s, %d\n", REGS[rs1], REGS[rs2], imm);
+      } else if (funct3 == 0b101) {
+        printf("bge %s, %s, %d\n", REGS[rs1], REGS[rs2], imm);
+      } else if (funct3 == 0b110) {
+        printf("bltu %s, %s, %d\n", REGS[rs1], REGS[rs2], imm);
+      } else if (funct3 == 0b111) {
+        printf("bgeu %s, %s, %d\n", REGS[rs1], REGS[rs2], imm);
+      } else {
+        fprintf(stderr, "B-type: unrecognized funct3: %03b\n", funct3);
+        exit(1);
+      }
+    }; break;
+    case 0b0010011: {
+      PARSE_I_INS(ins);
+
+      if (funct3 == 0b000) {
+        printf("addi %s, %s, %d\n", REGS[rd], REGS[rs1], imm);
+      } else if (funct3 == 0b001) {
+        u32 shamt = (ins >> 20) & 0b111111;
+        u32 funct6 = (ins >> 26) & 0b111111;
+
+        if (funct6 == 0b000000) {
+          printf("slli %s, %s, %d\n", REGS[rd], REGS[rs1], shamt);
+        } else {
+          fprintf(stderr, "I-type 1: funct3=001: unrecognized funct6: %b\n",
+                  funct6);
+          exit(1);
+        }
+      } else if (funct3 == 0b010) {
+        printf("slti %s, %s, %d\n", REGS[rd], REGS[rs1], imm);
+      } else if (funct3 == 0b011) {
+        printf("sltiu %s, %s, %d\n", REGS[rd], REGS[rs1], imm);
+      } else if (funct3 == 0b100) {
+        printf("xori %s, %s, %d\n", REGS[rd], REGS[rs1], imm);
+      } else if (funct3 == 0b101) {
+        // of course this one just has to be different
+        u32 shamt = (ins >> 20) & 0b111111;
+        u32 funct6 = (ins >> 26) & 0b111111;
+
+        if (funct6 == 0b000000) {
+          printf("srli %s, %s, %d\n", REGS[rd], REGS[rs1], shamt);
+        } else if (funct6 == 0b010000) {
+          printf("srai %s, %s, %d\n", REGS[rd], REGS[rs1], shamt);
+        } else {
+          fprintf(stderr, "I-type 1: funct3=101: unrecognized funct6: %b\n",
+                  funct6);
+          exit(1);
+        }
+      } else if (funct3 == 0b110) {
+        printf("ori %s, %s, %d\n", REGS[rd], REGS[rs1], imm);
+      } else if (funct3 == 0b111) {
+        printf("andi %s, %s, %d\n", REGS[rd], REGS[rs1], imm);
+      } else {
+        fprintf(stderr, "I-type 1: unrecognized funct3: %03b\n", funct3);
+        exit(1);
+      }
+    }; break;
+    case 0b0000011: {
+      PARSE_I_INS(ins);
+
+      if (funct3 == 0b000) {
+        printf("lb %s, %d(%s)\n", REGS[rd], imm, REGS[rs1]);
+      } else if (funct3 == 0b001) {
+        printf("lh %s, %d(%s)\n", REGS[rd], imm, REGS[rs1]);
+      } else if (funct3 == 0b010) {
+        printf("lw %s, %d(%s)\n", REGS[rd], imm, REGS[rs1]);
+      } else if (funct3 == 0b011) {
+        printf("ld %s, %d(%s)\n", REGS[rd], imm, REGS[rs1]);
+      } else if (funct3 == 0b100) {
+        printf("lbu %s, %d(%s)\n", REGS[rd], imm, REGS[rs1]);
+      } else if (funct3 == 0b101) {
+        printf("lhu %s, %d(%s)\n", REGS[rd], imm, REGS[rs1]);
+      } else if (funct3 == 0b110) {
+        printf("lwu %s, %d(%s)\n", REGS[rd], imm, REGS[rs1]);
+      } else {
+        fprintf(stderr, "I-type 2: unrecognized funct3: %03b\n", funct3);
+        exit(1);
+      }
+    }; break;
+    case 0b1100111: {
+      PARSE_I_INS(ins);
+      printf("jalr %s, %s, %d\n", REGS[rd], REGS[rs1], imm);
+    }; break;
+    case 0b1110011: {
+      PARSE_I_INS(ins);
+
+      if (funct3 == 0b000) {
+        if (imm == 0) {
+          printf("ecall\n");
+        } else {
+          fprintf(stderr, "I-type 4: funct3=000 unrecognized imm: %b\n", imm);
+          exit(1);
+        }
+      } else {
+        fprintf(stderr, "I-type 4: unrecognized funct3: %03b\n", funct3);
+        exit(1);
+      }
+    }; break;
+    case 0b1101111: {
+      PARSE_J_INS(ins);
+      printf("jal %s, %d\n", REGS[rd], imm);
+    }; break;
+    case 0b0110011: {
+      PARSE_R_INS(ins);
+      if (funct3 == 0b000) {
+        if (funct7 == 0b0000000) {
+          printf("add %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0100000) {
+          printf("sub %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0000001) {
+          printf("mul %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else {
+          fprintf(stderr, "R-type 1: funct3=0b000: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else if (funct3 == 0b001) {
+        if (funct7 == 0b0000000) {
+          printf("sll %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0000001) {
+          printf("mulh %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else {
+          fprintf(stderr, "R-type 1: funct3=0b001: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else if (funct3 == 0b010) {
+        if (funct7 == 0b0000000) {
+          printf("slt %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else {
+          fprintf(stderr, "R-type 1: funct3=0b010: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else if (funct3 == 0b011) {
+        if (funct7 == 0b0000000) {
+          printf("sltu %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0000001) {
+          printf("mulhu %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else {
+          fprintf(stderr, "R-type 1: funct3=0b011: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else if (funct3 == 0b100) {
+        if (funct7 == 0b0000000) {
+          printf("xor %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0000001) {
+          printf("div %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else {
+          fprintf(stderr, "R-type 1: funct3=0b100: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else if (funct3 == 0b101) {
+        if (funct7 == 0b0000000) {
+          printf("srl %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0000001) {
+          printf("divu %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0100000) {
+          printf("sra %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else {
+          fprintf(stderr, "R-type 1: funct3=0b101: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else if (funct3 == 0b110) {
+        if (funct7 == 0b0000001) {
+          printf("rem %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0000000) {
+          printf("or %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else {
+          fprintf(stderr, "R-type 1: funct3=0b110: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else if (funct3 == 0b111) {
+        if (funct7 == 0b000) {
+          printf("and %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b001) {
+          printf("remu %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else {
+          fprintf(stderr, "R-type 1: funct3=0b111: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else {
+        fprintf(stderr, "R-type 1: unrecognized funct3: %03b\n", funct3);
+        exit(1);
+      }
+    }; break;
+    case 0b0101111:
+      fprintf(stderr, "A extension not implemented yet.\n");
+      exit(1);
+    case 0b0111011: {
+      PARSE_R_INS(ins);
+      if (funct3 == 0b000) {
+        if (funct7 == 0b0000000) {
+          printf("addw %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0100000) {
+          printf("subw %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0000001) {
+          printf("mulw %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else {
+          fprintf(stderr, "R-type 3: funct3=000: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else if (funct3 == 0b001) {
+        printf("sllw %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+      } else if (funct3 == 0b100) {
+        printf("divw %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+      } else if (funct3 == 0b101) {
+        if (funct7 == 0b0000000) {
+          printf("srlw %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0100000) {
+          printf("sraw %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else if (funct7 == 0b0000001) {
+          printf("divuw %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+        } else {
+          fprintf(stderr, "R-type 3: funct3=101: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else if (funct3 == 0b110) {
+        printf("remw %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+      } else if (funct3 == 0b111) {
+        printf("remuw %s, %s, %s\n", REGS[rd], REGS[rs1], REGS[rs2]);
+      } else {
+        fprintf(stderr, "R-type 3: unrecognized funct3: %03b\n", funct3);
+        exit(1);
+      }
+    }; break;
+    case 0b0011011: {
+      u8 funct3 = (ins >> 12) & 0b111;
+      if (funct3 == 0b000) {
+        PARSE_I_INS(ins);
+        printf("addiw %s, %s, %d\n", REGS[rd], REGS[rs1], imm);
+      } else if (funct3 == 0b001) {
+        PARSE_R_INS(ins);
+        printf("slliw %s, %s, %d\n", REGS[rd], REGS[rs1], rs2);
+      } else if (funct3 == 0b101) {
+        PARSE_R_INS(ins);
+        if (funct7 == 0b0000000) {
+          printf("srliw %s, %s, %d\n", REGS[rd], REGS[rs1], rs2);
+        } else if (funct7 == 0b0100000) {
+          printf("sraiw %s, %s, %d\n", REGS[rd], REGS[rs1], rs2);
+        } else {
+          fprintf(stderr, "R-type 4: funct3=101: unrecognized funct7: %b\n",
+                  funct7);
+          exit(1);
+        }
+      } else {
+        fprintf(stderr, "R-type 4: unrecognized funct3: %03b\n", funct3);
+        exit(1);
+      }
+    }; break;
+    case 0b0100111: {
+      fprintf(stderr, "F extension not implemented yet.\n");
+      exit(1);
+    }; break;
+    case 0b0100011: {
+      PARSE_S_INS(ins);
+
+      if (funct3 == 0b000) {
+        printf("sb %s, %d(%s)\n", REGS[rs2], imm, REGS[rs1]);
+      } else if (funct3 == 0b001) {
+        printf("sh %s, %d(%s)\n", REGS[rs2], imm, REGS[rs1]);
+      } else if (funct3 == 0b010) {
+        printf("sw %s, %d(%s)\n", REGS[rs2], imm, REGS[rs1]);
+      } else if (funct3 == 0b011) {
+        printf("sd %s, %d(%s)\n", REGS[rs2], imm, REGS[rs1]);
+      } else {
+        fprintf(stderr, "S-type: unrecognized funct3: %03b\n", funct3);
+        exit(1);
+      }
+    }; break;
+    case 0b0110111: {
+      PARSE_U_INS(ins);
+      printf("lui %s, %d\n", REGS[rd], imm);
+    }; break;
+    case 0b0010111: {
+      PARSE_U_INS(ins);
+      printf("auipc %s, %d\n", REGS[rd], imm);
+    }; break;
+    default:
+      fprintf(stderr, "Unrecognized opcode: %07b\n", opcode);
+      exit(1);
+    }
+  }
+
+  void dump() {
+    std::cout << "REGS:";
+    for (u64 i = 0; i < 32; i++) {
+      std::cout << " " << m_regs[i];
+    }
+    std::cout << "\n";
+  }
+
+  void execute() {
+    m_pc = m_code_section.entrypoint;
+
+    m_regs[2] = MEMORY_SIZE - 1024; // set the stack pointer
+
+    while (m_pc < m_code_section.offset + m_code_section.size) {
+      m_regs[0] = 0; // clear the zero register
+
+      u32 ins;
+      std::memcpy(&ins, m_memory.data() + m_pc, sizeof(ins));
+
+      u16 opcode = ins & 0b1111111;
+
+      // https://stackoverflow.com/questions/62939410/how-can-i-find-out-the-instruction-format-of-a-risc-v-instruction
+      switch (opcode) {
+      case 0b1100011: {
+        PARSE_B_INS(ins);
+
+        if (funct3 == 0b000) { // beq
+          if (m_regs[rs1] == m_regs[rs2]) {
+            m_pc += imm;
+            continue;
+          }
+        } else if (funct3 == 0b001) { // bne
+          if (m_regs[rs1] != m_regs[rs2]) {
+            m_pc += imm;
+            continue;
+          }
+        } else if (funct3 == 0b101) { // bge
+          if (m_regs[rs1] >= m_regs[rs2]) {
+            m_pc += imm;
+            continue;
+          }
+        } else if (funct3 == 0b100) { // blt
+          if (m_regs[rs1] < m_regs[rs2]) {
+            m_pc += imm;
+            continue;
+          }
+        } else if (funct3 == 0b110) { // bltu
+          if ((u64)m_regs[rs1] < (u64)m_regs[rs2]) {
+            m_pc += imm;
+            continue;
+          }
+        } else {
+          fprintf(stderr, "B-type: unrecognized funct3: %03b\n", funct3);
+          exit(1);
+        }
+      }; break;
+      case 0b0010011: {
+        PARSE_I_INS(ins);
+
+        if (funct3 == 0b000) { // addi
+          m_regs[rd] = m_regs[rs1] + imm;
+        } else if (funct3 == 0b001) { // slli
+          u32 shamt = (ins >> 20) & 0b111111;
+          u32 funct6 = (ins >> 26) & 0b111111;
+
+          if (funct6 == 0b000000) {
+            m_regs[rd] = m_regs[rs1] << shamt;
+          } else {
+            fprintf(stderr, "I-type 1: funct3=001: unrecognized funct6: %b\n",
+                    funct6);
+            exit(1);
+          }
+        } else if (funct3 == 0b011) { // sltiu
+          m_regs[rd] = ((u64)m_regs[rs1] < (u64)(i64)imm) ? 1 : 0;
+        } else if (funct3 == 0b100) { // xori
+          m_regs[rd] = m_regs[rs1] ^ imm;
+        } else if (funct3 == 0b101) {
+          // of course this one just has to be different
+          u32 shamt = (ins >> 20) & 0b111111;
+          u32 funct6 = (ins >> 26) & 0b111111;
+
+          if (funct6 == 0b000000) { // srli
+            m_regs[rd] = (u64)m_regs[rs1] >> shamt;
+          } else if (funct6 == 0b010000) { // srai
+            m_regs[rd] = (i64)m_regs[rs1] >> shamt;
+          } else {
+            fprintf(stderr, "I-type 1: funct3=101: unrecognized funct6: %b\n",
+                    funct6);
+            exit(1);
+          }
+        } else if (funct3 == 0b111) {
+          m_regs[rd] = m_regs[rs1] & imm;
+        } else {
+          fprintf(stderr, "I-type 1: unrecognized funct3: %03b\n", funct3);
+          exit(1);
+        }
+      }; break;
+      case 0b0000011: {
+        PARSE_I_INS(ins);
+
+        if (funct3 == 0b000) { // lb
+          m_regs[rd] = (i8)m_memory[m_regs[rs1] + imm];
+        } else if (funct3 == 0b001) { // lh
+          m_regs[rd] = *(i16 *)&m_memory[m_regs[rs1] + imm];
+        } else if (funct3 == 0b010) { // lw
+          m_regs[rd] = *(i32 *)&m_memory[m_regs[rs1] + imm];
+        } else if (funct3 == 0b011) { // ld
+          m_regs[rd] = *(u64 *)&m_memory[m_regs[rs1] + imm];
+        } else if (funct3 == 0b100) { // lbu
+          m_regs[rd] = m_memory[m_regs[rs1] + imm];
+        } else {
+          fprintf(stderr, "I-type 2: unrecognized funct3: %03b\n", funct3);
+          exit(1);
+        }
+      }; break;
+      case 0b1100111: { // jalr
+        PARSE_I_INS(ins);
+        u64 target = (m_regs[rs1] + imm) & ~(u64)1;
+        m_regs[rd] = m_pc + 4;
+        m_pc = target;
+        continue;
+      }; break;
+      case 0b1110011: {
+        PARSE_I_INS(ins);
+
+        if (funct3 == 0b000) {
+          if (imm == 0) { // ecall
+            // https://jborza.com/post/2021-05-11-riscv-linux-syscalls/
+            switch (m_regs[17]) {
+            case 63: { // read
+              if (m_regs[10] != 0) {
+                fprintf(stderr, "read syscall implemented only for stdin.\n");
+                exit(1);
+              }
+
+              u64 start = m_regs[11];
+              u64 count = m_regs[12];
+              u64 bytes_read = 0;
+
+              for (u64 i = 0; i < count; i++) {
+                int c = getchar();
+                if (c == EOF)
+                  break;
+                m_memory[start + i] = (u8)c;
+                bytes_read++;
+                if (c == '\n')
+                  break;
+              }
+
+              m_regs[10] = bytes_read;
+            }; break;
+            case 64: { // write
+              if (m_regs[10] != 1) {
+                fprintf(stderr, "write syscall implemented only for stdout.\n");
+                exit(1);
+              }
+
+              u64 start = m_regs[11];
+              u64 end = m_regs[11] + m_regs[12];
+
+              for (u64 i = start; i < end; i++) {
+                putchar(m_memory[i]);
+              }
+            }; break;
+            case 93: { // exit
+              printf("Program exited with code %lu.\n", m_regs[10]);
+              return;
+            }; break;
+            case 169: { // gettimeofday
+                        // TODO: actually return the time
+              i64 tv_addr = m_regs[10];
+              i64 tz_addr = m_regs[11];
+
+              u8 tv_buf[16] = {
+                  0xD2, 0x02, 0x96, 0x49,
+                  0x00, 0x00, 0x00, 0x00, // tv_sec = 1234567890
+                  0x00, 0x00, 0x00, 0x00,
+                  0x00, 0x00, 0x00, 0x00, // tv_usec = 0
+              };
+              memcpy(&m_memory[tv_addr], tv_buf, 16);
+
+              memset(&m_memory[tz_addr], 0, 8);
+
+              m_regs[10] = 0;
+            }; break;
+            default:
+              fprintf(stderr, "Unimplemented syscall: %lu\n", m_regs[17]);
+              exit(1);
+            }
+            break;
+          } else {
+            fprintf(stderr, "I-type 4: funct3=000 unrecognized imm: %b\n", imm);
+            exit(1);
+          };
+          break;
+        } else {
+          fprintf(stderr, "I-type 4: unrecognized funct3: %03b\n", funct3);
+          exit(1);
+        }
+      }; break;
+      case 0b1101111: { // jal
+        PARSE_J_INS(ins);
+        m_regs[rd] = m_pc + 4;
+        m_pc += imm;
+        continue;
+      }; break;
+      case 0b0110011: {
+        PARSE_R_INS(ins);
+        if (funct3 == 0b000) {
+          if (funct7 == 0b0000000) { // add
+            m_regs[rd] = m_regs[rs1] + m_regs[rs2];
+          } else if (funct7 == 0b0100000) { // sub
+            m_regs[rd] = m_regs[rs1] - m_regs[rs2];
+          } else if (funct7 == 0b0000001) { // mul
+            m_regs[rd] = m_regs[rs1] * m_regs[rs2];
+          } else {
+            fprintf(stderr, "R-type 1: funct3=0b000: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else if (funct3 == 0b001) {
+          if (funct7 == 0b0000001) { // mulh
+            i64 a_hi = m_regs[rs1] >> 32;
+            i64 b_hi = m_regs[rs2] >> 32;
+            u64 a_lo = (u32)m_regs[rs1];
+            u64 b_lo = (u32)m_regs[rs2];
+            u64 p0 = a_lo * b_lo;
+            i64 p1 = a_hi * b_lo;
+            i64 p2 = b_hi * a_lo;
+            i64 p3 = a_hi * b_hi;
+            i64 carry = (p0 >> 32);
+            i64 mid = p1 + p2 + carry;
+            m_regs[rd] = p3 + (mid >> 32);
+          } else {
+            fprintf(stderr, "R-type 1: funct3=0b001: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else if (funct3 == 0b010) {
+          if (funct7 == 0b0000000) { // slt
+            m_regs[rd] = (m_regs[rs1] < m_regs[rs2]) ? 1 : 0;
+          } else {
+            fprintf(stderr, "R-type 1: funct3=0b010: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else if (funct3 == 0b011) {
+          if (funct7 == 0b0000000) { // sltu
+            m_regs[rd] = ((u64)m_regs[rs1] < (u64)m_regs[rs2]) ? 1 : 0;
+          } else if (funct7 == 0b0000001) { // mulhu
+            u64 a = m_regs[rs1];
+            u64 b = m_regs[rs2];
+            u64 a_lo = a & 0xffffffff;
+            u64 a_hi = a >> 32;
+            u64 b_lo = b & 0xffffffff;
+            u64 b_hi = b >> 32;
+            u64 lo_lo = a_lo * b_lo;
+            u64 hi_lo = a_hi * b_lo;
+            u64 lo_hi = a_lo * b_hi;
+            u64 hi_hi = a_hi * b_hi;
+            u64 mid =
+                (lo_lo >> 32) + (hi_lo & 0xffffffff) + (lo_hi & 0xffffffff);
+            m_regs[rd] = hi_hi + (hi_lo >> 32) + (lo_hi >> 32) + (mid >> 32);
+          } else {
+            fprintf(stderr, "R-type 1: funct3=0b011: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else if (funct3 == 0b100) {
+          if (funct7 == 0b0000000) { // xor
+            m_regs[rd] = m_regs[rs1] ^ m_regs[rs2];
+          } else if (funct7 == 0b0000001) { // div
+            if (m_regs[rs2] == 0) {
+              m_regs[rd] = -1;
+            } else {
+              m_regs[rd] = m_regs[rs1] / m_regs[rs2];
+            }
+          } else {
+            fprintf(stderr, "R-type 1: funct3=0b100: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else if (funct3 == 0b110) {
+          if (funct7 == 0b0000001) { // rem
+            if (m_regs[rs2] == 0) {
+              m_regs[rd] = m_regs[rs1];
+            } else {
+              m_regs[rd] = m_regs[rs1] % m_regs[rs2];
+            }
+          } else if (funct7 == 0b0000000) { // or
+            m_regs[rd] = m_regs[rs1] | m_regs[rs2];
+          } else {
+            fprintf(stderr, "R-type 1: funct3=0b110: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else if (funct3 == 0b111) {
+          if (funct7 == 0b000) { // and
+            m_regs[rd] = m_regs[rs1] & m_regs[rs2];
+          } else if (funct7 == 0b001) { // remu
+            if (m_regs[rs2] == 0) {
+              m_regs[rd] = m_regs[rs1];
+            } else {
+              m_regs[rd] = (u64)m_regs[rs1] % (u64)m_regs[rs2];
+            }
+          } else {
+            fprintf(stderr, "R-type 1: funct3=0b111: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else {
+          fprintf(stderr, "R-type 1: unrecognized funct3: %03b\n", funct3);
+          exit(1);
+        }
+      }; break;
+      case 0b0101111: {
+        fprintf(stderr, "A extension not implemented yet.\n");
+        exit(1);
+      }; break;
+      case 0b0111011: {
+        PARSE_R_INS(ins);
+        if (funct3 == 0b000) {
+          if (funct7 == 0b0000000) { // addw
+            m_regs[rd] = (i32)(m_regs[rs1] + m_regs[rs2]);
+          } else if (funct7 == 0b0100000) { // subw
+            m_regs[rd] = (i32)(m_regs[rs1] - m_regs[rs2]);
+          } else if (funct7 == 0b0000001) { // mulw
+            m_regs[rd] = (i32)(m_regs[rs1] * m_regs[rs2]);
+          } else {
+            fprintf(stderr, "R-type 3: funct3=000: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else if (funct3 == 0b001) {
+          if (funct7 == 0b0000000) { // sllw
+            m_regs[rd] =
+                (i32)(u32)((u32)m_regs[rs1] << ((u32)m_regs[rs2] & 0b11111));
+          } else {
+            fprintf(stderr, "R-type 3: funct3=001: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else if (funct3 == 0b100) { // divw
+          i32 a = m_regs[rs1];
+          i32 b = m_regs[rs2];
+          if (b == 0) {
+            m_regs[rd] = (u64)(i64)(-1);
+          } else {
+            m_regs[rd] = (i64)(a / b);
+          }
+        } else if (funct3 == 0b101) {
+          if (funct7 == 0b0000000) { // srlw
+            m_regs[rd] =
+                (i32)((u32)m_regs[rs1] >> ((u32)m_regs[rs2] & 0b11111));
+          } else if (funct7 == 0b0100000) { // sraw
+            m_regs[rd] = ((i32)m_regs[rs1]) >> ((u32)m_regs[rs2] & 0b11111);
+          } else if (funct7 == 0b0000001) { // divuw
+            if (m_regs[rs2] == 0) {
+              m_regs[rd] = -1LL;
+            } else {
+              m_regs[rd] = (i32)((u32)m_regs[rs1] / (u32)m_regs[rs2]);
+            }
+          } else {
+            fprintf(stderr, "R-type 3: funct3=101: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else if (funct3 == 0b111) { // remuw
+          if (m_regs[rs2] == 0) {
+            m_regs[rd] = (i32)m_regs[rs1];
+          } else {
+            m_regs[rd] = (i32)((u32)m_regs[rs1] % (u32)m_regs[rs2]);
+          }
+        } else {
+          fprintf(stderr, "R-type 3: unrecognized funct3: %03b\n", funct3);
+          exit(1);
+        }
+      }; break;
+      case 0b0011011: {
+        PARSE_I_INS(ins);
+        if (funct3 == 0b000) { // addiw
+          m_regs[rd] = (i32)m_regs[rs1] + (i32)imm;
+        } else if (funct3 == 0b001) {
+          u32 shamt = (ins >> 20) & 0b11111;
+          m_regs[rd] = (i32)m_regs[rs1] << shamt;
+        } else if (funct3 == 0b101) {
+          PARSE_R_INS(ins);
+          if (funct7 == 0b0000000) { // srliw
+            m_regs[rd] = (i32)((u32)m_regs[rs1] >> rs2);
+          } else if (funct7 == 0b0100000) { // sraiw
+            m_regs[rd] = (i32)m_regs[rs1] >> rs2;
+          } else {
+            fprintf(stderr, "R-type 4: funct3=101: unrecognized funct7: %b\n",
+                    funct7);
+            exit(1);
+          }
+        } else {
+          fprintf(stderr, "R-type 4: unrecognized funct3: %03b\n", funct3);
+          exit(1);
+        }
+      }; break;
+      case 0b0100011: {
+        PARSE_S_INS(ins);
+
+        if (funct3 == 0b000) { // sb
+          u64 addr = m_regs[rs1] + imm;
+          m_memory[addr] = m_regs[rs2];
+        } else if (funct3 == 0b001) { // sh
+          u64 addr = m_regs[rs1] + imm;
+          *(u16 *)(&m_memory[addr]) = m_regs[rs2];
+        } else if (funct3 == 0b010) { // sw
+          u64 addr = m_regs[rs1] + imm;
+          *(u32 *)(&m_memory[addr]) = m_regs[rs2];
+        } else if (funct3 == 0b011) { // sd
+          u64 addr = m_regs[rs1] + imm;
+          // take this rust
+          *(u64 *)(&m_memory[addr]) = m_regs[rs2];
+        } else {
+          fprintf(stderr, "S-type: unrecognized funct3: %03b\n", funct3);
+          exit(1);
+        }
+      }; break;
+      case 0b0110111: { // lui
+        PARSE_U_INS(ins);
+        m_regs[rd] = (i64)(i32)(imm << 12);
+      }; break;
+      case 0b0010111: { // auipc
+        PARSE_U_INS(ins);
+        m_regs[rd] = m_pc + ((i64)imm << 12);
+      }; break;
+      default:
+        fprintf(stderr, "Unrecognized opcode: %07b\n", opcode);
+        exit(1);
+      }
+
+      m_pc += 4;
+    }
+  }
+
 private:
   std::vector<u8> m_memory = std::vector<u8>(MEMORY_SIZE, 0);
   u64 m_pc;
-  std::array<i64, 32> m_regs = {0};
+  std::array<i64, 32> m_regs{};
   Section m_code_section;
 
   static Section get_code_section(Elf *elf, GElf_Ehdr ehdr) {
@@ -117,10 +923,11 @@ int main(int argc, char *argv[]) {
 
   RISCV64 r(exe_bytes);
 
-  exe_bytes = {};
+  exe_bytes.clear();
+  exe_bytes.shrink_to_fit();
 
-  // r.disassemble_all();
+  r.disassemble_all();
-  // printf("END DISASSEMBLY\n");
+  printf("END DISASSEMBLY\n");
 
-  // r.execute();
+  r.execute();
 }