Merge pull request #2903 from o1-labs/dw/div-by-zero

o1vm/riscv32im: div by zero for DIV and DIVU

o1vm/resources/programs/riscv32im/src/div_by_zero.S

@@ -0,0 +1,19 @@
+.section .text
+.globl _start
+
+_start:
+    # Signed division by zero (div)
+    li t0, 42             # t0 = 42
+    li t1, 0              # t1 = 0
+    div t2, t0, t1        # t2 = t0 / t1 (Expected: division by zero)
+
+    # Custom exit syscall
+    li a0, 0
+    li a1, 0
+    li a2, 0
+    li a3, 0
+    li a4, 0
+    li a5, 0
+    li a6, 0
+    li a7, 42
+    ecall

o1vm/resources/programs/riscv32im/src/divu_by_zero.S

@@ -0,0 +1,19 @@
+.section .text
+.globl _start
+
+_start:
+    # Unsigned division by zero (div)
+    li t0, 42             # t0 = 42
+    li t1, 0              # t1 = 0
+    divu t2, t0, t1       # t2 = t0 / t1 (Expected: division by zero)
+
+    # Custom exit syscall
+    li a0, 0
+    li a1, 0
+    li a2, 0
+    li a3, 0
+    li a4, 0
+    li a5, 0
+    li a6, 0
+    li a7, 42
+    ecall

o1vm/src/interpreters/riscv32im/interpreter.rs

@@ -1280,6 +1280,10 @@ pub trait InterpreterEnv {
     /// There are no constraints on the returned values; callers must manually add constraints to
     /// ensure that the pair of returned values correspond to the given values `x` and `y`, and
     /// that they fall within the desired range.
+    ///
+    /// Division by zero will create a panic! exception. The RISC-V
+    /// specification leaves the case unspecified, and therefore we prefer to
+    /// forbid this case while building the witness.
     unsafe fn div_signed(
         &mut self,
         x: &Self::Variable,
@@ -1308,6 +1312,10 @@ pub trait InterpreterEnv {
     /// There are no constraints on the returned values; callers must manually add constraints to
     /// ensure that the pair of returned values correspond to the given values `x` and `y`, and
     /// that they fall within the desired range.
+    ///
+    /// Division by zero will create a panic! exception. The RISC-V
+    /// specification leaves the case unspecified, and therefore we prefer to
+    /// forbid this case while building the witness.
     unsafe fn div(
         &mut self,
         x: &Self::Variable,

o1vm/tests/test_riscv_elf.rs

@@ -356,3 +356,33 @@ fn test_slt() {
     assert_eq!(witness.registers[T5], 0);
     assert_eq!(witness.registers[T6], 0);
 }
+
+#[test]
+#[should_panic]
+fn test_div_by_zero() {
+    let curr_dir = std::env::current_dir().unwrap();
+    let path = curr_dir.join(std::path::PathBuf::from(
+        "resources/programs/riscv32im/bin/div_by_zero",
+    ));
+    let state = o1vm::elf_loader::parse_riscv32(&path).unwrap();
+    let mut witness = Env::<Fp>::create(PAGE_SIZE.try_into().unwrap(), state);
+
+    while !witness.halt {
+        witness.step();
+    }
+}
+
+#[test]
+#[should_panic]
+fn test_divu_by_zero() {
+    let curr_dir = std::env::current_dir().unwrap();
+    let path = curr_dir.join(std::path::PathBuf::from(
+        "resources/programs/riscv32im/bin/divu_by_zero",
+    ));
+    let state = o1vm::elf_loader::parse_riscv32(&path).unwrap();
+    let mut witness = Env::<Fp>::create(PAGE_SIZE.try_into().unwrap(), state);
+
+    while !witness.halt {
+        witness.step();
+    }
+}