diff --git a/artiq/compiler/ir.py b/artiq/compiler/ir.py
index e62ca3dfc..6ae9bdf76 100644
--- a/artiq/compiler/ir.py
+++ b/artiq/compiler/ir.py
@@ -36,13 +36,6 @@ class TKeyword(types.TMono):
 def is_keyword(typ):
     return isinstance(typ, TKeyword)
 
-class TExceptionTypeInfo(types.TMono):
-    def __init__(self):
-        super().__init__("exntypeinfo")
-
-def is_exn_typeinfo(typ):
-    return isinstance(typ, TExceptionTypeInfo)
-
 class Value:
     """
     An SSA value that keeps track of its uses.
diff --git a/artiq/compiler/transforms/artiq_ir_generator.py b/artiq/compiler/transforms/artiq_ir_generator.py
index 3ad09f300..518335e2f 100644
--- a/artiq/compiler/transforms/artiq_ir_generator.py
+++ b/artiq/compiler/transforms/artiq_ir_generator.py
@@ -1332,10 +1332,6 @@ class ARTIQIRGenerator(algorithm.Visitor):
                 rhs_length = self.iterable_len(rhs)
 
                 result_length = self.append(ir.Arith(ast.Add(loc=None), lhs_length, rhs_length))
-                if builtins.is_str(node.left.type):
-                    result_last   = result_length
-                    result_length = self.append(ir.Arith(ast.Add(loc=None), result_length,
-                                                         ir.Constant(1, self._size_type)))
                 result = self.append(ir.Alloc([result_length], node.type))
 
                 # Copy lhs
@@ -1359,10 +1355,6 @@ class ARTIQIRGenerator(algorithm.Visitor):
                     lambda index: self.append(ir.Compare(ast.Lt(loc=None), index, rhs_length)),
                     body_gen)
 
-                if builtins.is_str(node.left.type):
-                    self.append(ir.SetElem(result, result_last,
-                                           ir.Constant(0, builtins.TInt(types.TValue(8)))))
-
                 return result
             else:
                 assert False
@@ -1564,13 +1556,13 @@ class ARTIQIRGenerator(algorithm.Visitor):
     # Keep this function with builtins.TException.attributes.
     def alloc_exn(self, typ, message=None, param0=None, param1=None, param2=None):
         typ = typ.find()
+        name = "{}:{}".format(typ.id, typ.name)
         attributes = [
-            ir.Constant("{}:{}".format(typ.id, typ.name),
-                        ir.TExceptionTypeInfo()),         # typeinfo
-            ir.Constant("<not thrown>", builtins.TStr()), # file
-            ir.Constant(0, builtins.TInt32()),            # line
-            ir.Constant(0, builtins.TInt32()),            # column
-            ir.Constant("<not thrown>", builtins.TStr()), # function
+            ir.Constant(name,           builtins.TStr()),   # typeinfo
+            ir.Constant("<not thrown>", builtins.TStr()),   # file
+            ir.Constant(0,              builtins.TInt32()), # line
+            ir.Constant(0,              builtins.TInt32()), # column
+            ir.Constant("<not thrown>", builtins.TStr()),   # function
         ]
 
         if message is None:
@@ -1892,7 +1884,7 @@ class ARTIQIRGenerator(algorithm.Visitor):
         else:
             explanation = node.loc.source()
         self.append(ir.Builtin("printf", [
-                ir.Constant("assertion failed at %s: %s\n", builtins.TStr()),
+                ir.Constant("assertion failed at %.*s: %.*s\n\x00", builtins.TStr()),
                 ir.Constant(str(node.loc.begin()), builtins.TStr()),
                 ir.Constant(str(explanation), builtins.TStr()),
             ], builtins.TNone()))
@@ -1905,7 +1897,7 @@ class ARTIQIRGenerator(algorithm.Visitor):
 
             subexpr_body = self.current_block = self.add_block("assert.subexpr.body")
             self.append(ir.Builtin("printf", [
-                    ir.Constant("  (%s) = ", builtins.TStr()),
+                    ir.Constant("  (%.*s) = \x00", builtins.TStr()),
                     ir.Constant(subexpr_node.loc.source(), builtins.TStr())
                 ], builtins.TNone()))
             subexpr_value = self.append(ir.Builtin("unwrap", [subexpr_value_opt],
@@ -1937,7 +1929,7 @@ class ARTIQIRGenerator(algorithm.Visitor):
         def flush():
             nonlocal format_string, args
             if format_string != "":
-                printf(format_string, *args)
+                printf(format_string + "\x00", *args)
                 format_string = ""
                 args = []
 
@@ -1961,7 +1953,7 @@ class ARTIQIRGenerator(algorithm.Visitor):
             elif builtins.is_none(value.type):
                 format_string += "None"
             elif builtins.is_bool(value.type):
-                format_string += "%s"
+                format_string += "%.*s"
                 args.append(self.append(ir.Select(value,
                                                   ir.Constant("True", builtins.TStr()),
                                                   ir.Constant("False", builtins.TStr()))))
@@ -1979,9 +1971,9 @@ class ARTIQIRGenerator(algorithm.Visitor):
                 args.append(value)
             elif builtins.is_str(value.type):
                 if as_repr:
-                    format_string += "\"%s\""
+                    format_string += "\"%.*s\""
                 else:
-                    format_string += "%s"
+                    format_string += "%.*s"
                 args.append(value)
             elif builtins.is_listish(value.type):
                 if builtins.is_list(value.type):
@@ -2000,7 +1992,7 @@ class ARTIQIRGenerator(algorithm.Visitor):
                     head = self.current_block
 
                     if_last = self.current_block = self.add_block("print.comma")
-                    printf(", ")
+                    printf(", \x00")
 
                     tail = self.current_block = self.add_block("print.tail")
                     if_last.append(ir.Branch(tail))
@@ -2032,7 +2024,7 @@ class ARTIQIRGenerator(algorithm.Visitor):
                 param2  = self.append(ir.GetAttr(value, "__param1__"))
                 param3  = self.append(ir.GetAttr(value, "__param2__"))
 
-                format_string += "%s(%s, %lld, %lld, %lld)"
+                format_string += "%.*s(%.*s, %lld, %lld, %lld)"
                 args += [name, message, param1, param2, param3]
             else:
                 assert False
diff --git a/artiq/compiler/transforms/llvm_ir_generator.py b/artiq/compiler/transforms/llvm_ir_generator.py
index 706afbadc..b51c9e288 100644
--- a/artiq/compiler/transforms/llvm_ir_generator.py
+++ b/artiq/compiler/transforms/llvm_ir_generator.py
@@ -20,6 +20,8 @@ lli64      = ll.IntType(64)
 lldouble   = ll.DoubleType()
 llptr      = ll.IntType(8).as_pointer()
 llptrptr   = ll.IntType(8).as_pointer().as_pointer()
+llslice    = ll.LiteralStructType([llptr, lli32])
+llsliceptr = ll.LiteralStructType([llptr, lli32]).as_pointer()
 llmetadata = ll.MetaData()
 
 
@@ -216,8 +218,6 @@ class LLVMIRGenerator:
             return ll.IntType(builtins.get_int_width(typ))
         elif builtins.is_float(typ):
             return lldouble
-        elif builtins.is_str(typ) or ir.is_exn_typeinfo(typ):
-            return llptr
         elif builtins.is_listish(typ):
             lleltty = self.llty_of_type(builtins.get_iterable_elt(typ))
             return ll.LiteralStructType([lleltty.as_pointer(), lli32])
@@ -229,7 +229,7 @@ class LLVMIRGenerator:
         elif ir.is_option(typ):
             return ll.LiteralStructType([lli1, self.llty_of_type(typ.params["value"])])
         elif ir.is_keyword(typ):
-            return ll.LiteralStructType([llptr, self.llty_of_type(typ.params["value"])])
+            return ll.LiteralStructType([llslice, self.llty_of_type(typ.params["value"])])
         elif ir.is_environment(typ):
             llty = self.llcontext.get_identified_type("env.{}".format(typ.env_name))
             if llty.elements is None:
@@ -262,8 +262,7 @@ class LLVMIRGenerator:
 
     def llstr_of_str(self, value, name=None, linkage="private", unnamed_addr=True):
         if isinstance(value, str):
-            assert "\0" not in value
-            as_bytes = (value + "\0").encode("utf-8")
+            as_bytes = value.encode("utf-8")
         else:
             as_bytes = value
 
@@ -295,19 +294,14 @@ class LLVMIRGenerator:
         elif isinstance(const.value, (int, float)):
             return ll.Constant(llty, const.value)
         elif isinstance(const.value, (str, bytes)):
-            if ir.is_exn_typeinfo(const.type):
-                # Exception typeinfo; should be merged with identical others
-                name = "__artiq_exn_" + const.value
-                linkage = "linkonce"
-                unnamed_addr = False
+            if isinstance(const.value, str):
+                value = const.value.encode('utf-8')
             else:
-                # Just a string
-                name = None
-                linkage = "private"
-                unnamed_addr = True
+                value = const.value
 
-            return self.llstr_of_str(const.value, name=name,
-                                     linkage=linkage, unnamed_addr=unnamed_addr)
+            llptr = self.llstr_of_str(const.value, linkage="private", unnamed_addr=True)
+            lllen = ll.Constant(lli32, len(const.value))
+            return ll.Constant(llty, (llptr, lllen))
         else:
             assert False
 
@@ -318,8 +312,6 @@ class LLVMIRGenerator:
 
         if name in "llvm.donothing":
             llty = ll.FunctionType(llvoid, [])
-        elif name in "llvm.trap":
-            llty = ll.FunctionType(llvoid, [])
         elif name == "llvm.floor.f64":
             llty = ll.FunctionType(lldouble, [lldouble])
         elif name == "llvm.round.f64":
@@ -344,14 +336,14 @@ class LLVMIRGenerator:
             llty = ll.FunctionType(llvoid, [self.llty_of_type(builtins.TException())])
         elif name == "__artiq_reraise":
             llty = ll.FunctionType(llvoid, [])
-        elif name == "strlen":
-            llty = ll.FunctionType(lli32, [llptr])
-        elif name == "strcmp":
-            llty = ll.FunctionType(lli32, [llptr, llptr])
+        elif name in "abort":
+            llty = ll.FunctionType(llvoid, [])
+        elif name == "memcmp":
+            llty = ll.FunctionType(lli32, [llptr, llptr, lli32])
         elif name == "send_rpc":
-            llty = ll.FunctionType(llvoid, [lli32, llptr, llptrptr])
+            llty = ll.FunctionType(llvoid, [lli32, llsliceptr, llptrptr])
         elif name == "send_async_rpc":
-            llty = ll.FunctionType(llvoid, [lli32, llptr, llptrptr])
+            llty = ll.FunctionType(llvoid, [lli32, llsliceptr, llptrptr])
         elif name == "recv_rpc":
             llty = ll.FunctionType(lli32, [llptr])
         elif name == "now":
@@ -423,7 +415,7 @@ class LLVMIRGenerator:
                 llobjects[obj_typ].append(llobject.bitcast(llptr))
 
         llrpcattrty = self.llcontext.get_identified_type("A")
-        llrpcattrty.elements = [lli32, llptr, llptr]
+        llrpcattrty.elements = [lli32, llslice, llslice]
 
         lldescty = self.llcontext.get_identified_type("D")
         lldescty.elements = [llrpcattrty.as_pointer().as_pointer(), llptr.as_pointer()]
@@ -445,15 +437,14 @@ class LLVMIRGenerator:
 
                 if not (types.is_function(typ) or types.is_method(typ) or types.is_rpc(typ) or
                         name == "__objectid__"):
-                    rpctag   = b"Os" + self._rpc_tag(typ, error_handler=rpc_tag_error) + b":n\x00"
-                    llrpctag = self.llstr_of_str(rpctag)
+                    rpctag = b"Os" + self._rpc_tag(typ, error_handler=rpc_tag_error) + b":n"
                 else:
-                    llrpctag = ll.Constant(llptr, None)
+                    rpctag = b""
 
                 llrpcattrinit = ll.Constant(llrpcattrty, [
                     ll.Constant(lli32, offset),
-                    llrpctag,
-                    self.llstr_of_str(name)
+                    self.llconst_of_const(ir.Constant(rpctag, builtins.TStr())),
+                    self.llconst_of_const(ir.Constant(name, builtins.TStr()))
                 ])
 
                 if name == "__objectid__":
@@ -615,10 +606,6 @@ class LLVMIRGenerator:
                                                    name=insn.name)
             else:
                 assert False
-        elif builtins.is_str(insn.type):
-            llsize = self.map(insn.operands[0])
-            llvalue = self.llbuilder.alloca(lli8, size=llsize)
-            return llvalue
         elif builtins.is_listish(insn.type):
             llsize = self.map(insn.operands[0])
             lleltty = self.llty_of_type(builtins.get_iterable_elt(insn.type))
@@ -829,13 +816,9 @@ class LLVMIRGenerator:
     def process_GetElem(self, insn):
         lst, idx = insn.list(), insn.index()
         lllst, llidx = map(self.map, (lst, idx))
-        if builtins.is_str(lst.type):
-            llelt = self.llbuilder.gep(lllst, [llidx], inbounds=True)
-            llvalue = self.llbuilder.load(llelt)
-        else:
-            llelts = self.llbuilder.extract_value(lllst, 0)
-            llelt = self.llbuilder.gep(llelts, [llidx], inbounds=True)
-            llvalue = self.llbuilder.load(llelt)
+        llelts = self.llbuilder.extract_value(lllst, 0)
+        llelt = self.llbuilder.gep(llelts, [llidx], inbounds=True)
+        llvalue = self.llbuilder.load(llelt)
         if isinstance(llvalue.type, ll.PointerType):
             self.mark_dereferenceable(llvalue)
         return llvalue
@@ -843,11 +826,8 @@ class LLVMIRGenerator:
     def process_SetElem(self, insn):
         lst, idx = insn.list(), insn.index()
         lllst, llidx = map(self.map, (lst, idx))
-        if builtins.is_str(lst.type):
-            llelt = self.llbuilder.gep(lllst, [llidx], inbounds=True)
-        else:
-            llelts = self.llbuilder.extract_value(lllst, 0)
-            llelt = self.llbuilder.gep(llelts, [llidx], inbounds=True)
+        llelts = self.llbuilder.extract_value(lllst, 0)
+        llelt = self.llbuilder.gep(llelts, [llidx], inbounds=True)
         return self.llbuilder.store(self.map(insn.value()), llelt)
 
     def process_Coerce(self, insn):
@@ -1029,7 +1009,7 @@ class LLVMIRGenerator:
         if insn.op == "nop":
             return self.llbuilder.call(self.llbuiltin("llvm.donothing"), [])
         if insn.op == "abort":
-            return self.llbuilder.call(self.llbuiltin("llvm.trap"), [])
+            return self.llbuilder.call(self.llbuiltin("abort"), [])
         elif insn.op == "is_some":
             lloptarg = self.map(insn.operands[0])
             return self.llbuilder.extract_value(lloptarg, 0,
@@ -1066,15 +1046,21 @@ class LLVMIRGenerator:
             return get_outer(self.map(env), env.type)
         elif insn.op == "len":
             collection, = insn.operands
-            if builtins.is_str(collection.type):
-                return self.llbuilder.call(self.llbuiltin("strlen"), [self.map(collection)])
-            else:
-                return self.llbuilder.extract_value(self.map(collection), 1)
+            return self.llbuilder.extract_value(self.map(collection), 1)
         elif insn.op in ("printf", "rtio_log"):
             # We only get integers, floats, pointers and strings here.
-            llargs = map(self.map, insn.operands)
+            lloperands = []
+            for i, operand in enumerate(insn.operands):
+                lloperand = self.map(operand)
+                if i == 0 and insn.op == "printf" or i == 1 and insn.op == "rtio_log":
+                    lloperands.append(self.llbuilder.extract_value(lloperand, 0))
+                elif builtins.is_str(operand.type):
+                    lloperands.append(self.llbuilder.extract_value(lloperand, 1))
+                    lloperands.append(self.llbuilder.extract_value(lloperand, 0))
+                else:
+                    lloperands.append(lloperand)
             func_name = self.target.print_function if insn.op == "printf" else insn.op
-            return self.llbuilder.call(self.llbuiltin(func_name), llargs,
+            return self.llbuilder.call(self.llbuiltin(func_name), lloperands,
                                        name=insn.name)
         elif insn.op == "exncast":
             # This is an identity cast at LLVM IR level.
@@ -1231,9 +1217,10 @@ class LLVMIRGenerator:
                 fun_loc)
             self.engine.process(diag)
         tag += self._rpc_tag(fun_type.ret, ret_error_handler)
-        tag += b"\x00"
 
-        lltag = self.llstr_of_str(tag)
+        lltag = self.llconst_of_const(ir.Constant(tag, builtins.TStr()))
+        lltagptr = self.llbuilder.alloca(lltag.type)
+        self.llbuilder.store(lltag, lltagptr)
 
         llstackptr = self.llbuilder.call(self.llbuiltin("llvm.stacksave"), [],
                                          name="rpc.stack")
@@ -1256,10 +1243,10 @@ class LLVMIRGenerator:
 
         if fun_type.async:
             self.llbuilder.call(self.llbuiltin("send_async_rpc"),
-                                [llservice, lltag, llargs])
+                                [llservice, lltagptr, llargs])
         else:
             self.llbuilder.call(self.llbuiltin("send_rpc"),
-                                [llservice, lltag, llargs])
+                                [llservice, lltagptr, llargs])
 
         # Don't waste stack space on saved arguments.
         self.llbuilder.call(self.llbuiltin("llvm.stackrestore"), [llstackptr])
@@ -1446,19 +1433,16 @@ class LLVMIRGenerator:
         elif builtins.is_float(typ):
             assert isinstance(value, float)
             return ll.Constant(llty, value)
-        elif builtins.is_str(typ):
-            assert isinstance(value, (str, bytes))
-            return self.llstr_of_str(value)
         elif builtins.is_listish(typ):
-            assert isinstance(value, (list, numpy.ndarray))
+            assert isinstance(value, (str, bytes, list, numpy.ndarray))
             elt_type  = builtins.get_iterable_elt(typ)
             llelts    = [self._quote(value[i], elt_type, lambda: path() + [str(i)])
                          for i in range(len(value))]
             lleltsary = ll.Constant(ll.ArrayType(self.llty_of_type(elt_type), len(llelts)),
                                     list(llelts))
 
-            llglobal  = ll.GlobalVariable(self.llmodule, lleltsary.type,
-                                          self.llmodule.scope.deduplicate("quoted.list"))
+            name      = self.llmodule.scope.deduplicate("quoted.{}".format(typ.name))
+            llglobal  = ll.GlobalVariable(self.llmodule, lleltsary.type, name)
             llglobal.initializer = lleltsary
             llglobal.linkage = "private"
 
@@ -1556,23 +1540,38 @@ class LLVMIRGenerator:
 
         for target, typ in insn.clauses():
             if typ is None:
-                llclauseexnname = ll.Constant(
-                    self.llty_of_type(ir.TExceptionTypeInfo()), None)
+                llclauseexnnameptr = ll.Constant(
+                    self.llty_of_type(builtins.TStr()).as_pointer(), None)
             else:
+                exnname = "{}:{}".format(typ.id, typ.name)
                 llclauseexnname = self.llconst_of_const(
-                    ir.Constant("{}:{}".format(typ.id, typ.name),
-                                ir.TExceptionTypeInfo()))
-            lllandingpad.add_clause(ll.CatchClause(llclauseexnname))
+                    ir.Constant(exnname, builtins.TStr()))
+
+                llclauseexnnameptr = self.llmodule.get_global("exn.{}".format(exnname))
+                if llclauseexnnameptr is None:
+                    llclauseexnnameptr = ll.GlobalVariable(self.llmodule, llclauseexnname.type,
+                                                           name="exn.{}".format(exnname))
+                    llclauseexnnameptr.global_constant = True
+                    llclauseexnnameptr.initializer = llclauseexnname
+                    llclauseexnnameptr.linkage = "private"
+                    llclauseexnnameptr.unnamed_addr = True
+            lllandingpad.add_clause(ll.CatchClause(llclauseexnnameptr))
 
             if typ is None:
                 self.llbuilder.branch(self.map(target))
             else:
-                llexnmatch = self.llbuilder.call(self.llbuiltin("strcmp"),
-                                                 [llexnname, llclauseexnname])
-                llmatchingclause = self.llbuilder.icmp_unsigned('==',
-                                                                llexnmatch, ll.Constant(lli32, 0))
-                with self.llbuilder.if_then(llmatchingclause):
-                    self.llbuilder.branch(self.map(target))
+                llexnlen       = self.llbuilder.extract_value(llexnname, 1)
+                llclauseexnlen = self.llbuilder.extract_value(llclauseexnname, 1)
+                llmatchinglen  = self.llbuilder.icmp_unsigned('==', llexnlen, llclauseexnlen)
+                with self.llbuilder.if_then(llmatchinglen):
+                    llexnptr       = self.llbuilder.extract_value(llexnname, 0)
+                    llclauseexnptr = self.llbuilder.extract_value(llclauseexnname, 0)
+                    llcomparedata  = self.llbuilder.call(self.llbuiltin("memcmp"),
+                                                         [llexnptr, llclauseexnptr, llexnlen])
+                    llmatchingdata = self.llbuilder.icmp_unsigned('==', llcomparedata,
+                                                                  ll.Constant(lli32, 0))
+                    with self.llbuilder.if_then(llmatchingdata):
+                        self.llbuilder.branch(self.map(target))
 
         if self.llbuilder.basic_block.terminator is None:
             self.llbuilder.branch(self.map(insn.cleanup()))
diff --git a/artiq/firmware/Cargo.lock b/artiq/firmware/Cargo.lock
index 196fef089..683195487 100644
--- a/artiq/firmware/Cargo.lock
+++ b/artiq/firmware/Cargo.lock
@@ -115,6 +115,7 @@ dependencies = [
  "build_artiq 0.0.0",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "compiler_builtins 0.1.0 (git+https://github.com/rust-lang-nursery/compiler-builtins)",
+ "cslice 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "fringe 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "logger_artiq 0.0.0",
diff --git a/artiq/firmware/ksupport/api.rs b/artiq/firmware/ksupport/api.rs
index 43e44e032..ea1093caf 100644
--- a/artiq/firmware/ksupport/api.rs
+++ b/artiq/firmware/ksupport/api.rs
@@ -1,8 +1,6 @@
-use libc::{c_void, c_char, size_t};
-
 macro_rules! api {
     ($i:ident) => ({
-        extern { static $i: c_void; }
+        extern { static $i: u8; }
         api!($i = &$i as *const _)
     });
     ($i:ident, $d:item) => ({
@@ -68,9 +66,8 @@ static mut API: &'static [(&'static str, *const ())] = &[
     api!(__powidf2),
 
     /* libc */
-    api!(strcmp),
-    api!(strlen, extern { fn strlen(s: *const c_char) -> size_t; }),
     api!(abort = ::abort),
+    api!(memcmp, extern { fn memcmp(a: *const u8, b: *mut u8, size: usize); }),
 
     /* libm */
     api!(sqrt),
diff --git a/artiq/firmware/ksupport/lib.rs b/artiq/firmware/ksupport/lib.rs
index 3c2d62333..92959d26b 100644
--- a/artiq/firmware/ksupport/lib.rs
+++ b/artiq/firmware/ksupport/lib.rs
@@ -30,15 +30,14 @@ extern {
 macro_rules! artiq_raise {
     ($name:expr, $message:expr, $param0:expr, $param1:expr, $param2:expr) => ({
         let exn = $crate::kernel_proto::Exception {
-            name:     concat!("0:artiq.coredevice.exceptions.", $name, "\0").as_bytes().as_ptr(),
-            file:     concat!(file!(), "\0").as_bytes().as_ptr(),
+            name:     concat!("0:artiq.coredevice.exceptions.", $name),
+            file:     file!(),
             line:     line!(),
             column:   column!(),
             // https://github.com/rust-lang/rfcs/pull/1719
-            function: "(Rust function)\0".as_bytes().as_ptr(),
-            message:  concat!($message, "\0").as_bytes().as_ptr(),
-            param:    [$param0, $param1, $param2],
-            phantom:  ::core::marker::PhantomData
+            function: "(Rust function)",
+            message:  $message,
+            param:    [$param0, $param1, $param2]
         };
         #[allow(unused_unsafe)]
         unsafe { $crate::__artiq_raise(&exn as *const _) }
@@ -48,9 +47,8 @@ macro_rules! artiq_raise {
     });
 }
 
-use core::{mem, ptr, slice, str};
+use core::{mem, ptr, str};
 use std::io::Cursor;
-use libc::{c_char, size_t};
 use cslice::{CSlice, CMutSlice, AsCSlice};
 use kernel_proto::*;
 use dyld::Library;
@@ -125,28 +123,22 @@ extern fn abort() -> ! {
     loop {}
 }
 
-extern fn send_rpc(service: u32, tag: *const u8, data: *const *const ()) {
-    extern { fn strlen(s: *const c_char) -> size_t; }
-    let tag = unsafe { slice::from_raw_parts(tag, strlen(tag as *const c_char)) };
-
+extern fn send_rpc(service: u32, tag: CSlice<u8>, data: *const *const ()) {
     while !rpc_queue::empty() {}
     send(&RpcSend {
         async:   false,
         service: service,
-        tag:     tag,
+        tag:     tag.as_ref(),
         data:    data
     })
 }
 
-extern fn send_async_rpc(service: u32, tag: *const u8, data: *const *const ()) {
-    extern { fn strlen(s: *const c_char) -> size_t; }
-    let tag = unsafe { slice::from_raw_parts(tag, strlen(tag as *const c_char)) };
-
+extern fn send_async_rpc(service: u32, tag: CSlice<u8>, data: *const *const ()) {
     while rpc_queue::full() {}
     rpc_queue::enqueue(|mut slice| {
         let length = {
             let mut writer = Cursor::new(&mut slice[4..]);
-            rpc_proto::send_args(&mut writer, service, tag, data)?;
+            rpc_proto::send_args(&mut writer, service, tag.as_ref(), data)?;
             writer.position()
         };
         proto::write_u32(&mut slice, length as u32)
@@ -157,7 +149,7 @@ extern fn send_async_rpc(service: u32, tag: *const u8, data: *const *const ()) {
         send(&RpcSend {
             async:   true,
             service: service,
-            tag:     tag,
+            tag:     tag.as_ref(),
             data:    data
         })
     })
@@ -206,21 +198,18 @@ extern fn watchdog_clear(id: i32) {
     send(&WatchdogClear { id: id as usize })
 }
 
-extern fn cache_get(key: *const u8) -> CSlice<'static, i32> {
-    extern { fn strlen(s: *const c_char) -> size_t; }
-    let key = unsafe { slice::from_raw_parts(key, strlen(key as *const c_char)) };
-    let key = unsafe { str::from_utf8_unchecked(key) };
-
-    send(&CacheGetRequest { key: key });
+extern fn cache_get(key: CSlice<u8>) -> CSlice<'static, i32> {
+    send(&CacheGetRequest {
+        key:   str::from_utf8(key.as_ref()).unwrap()
+    });
     recv!(&CacheGetReply { value } => value.as_c_slice())
 }
 
-extern fn cache_put(key: *const u8, list: CSlice<i32>) {
-    extern { fn strlen(s: *const c_char) -> size_t; }
-    let key = unsafe { slice::from_raw_parts(key, strlen(key as *const c_char)) };
-    let key = unsafe { str::from_utf8_unchecked(key) };
-
-    send(&CachePutRequest { key: key, value: list.as_ref() });
+extern fn cache_put(key: CSlice<u8>, list: CSlice<i32>) {
+    send(&CachePutRequest {
+        key:   str::from_utf8(key.as_ref()).unwrap(),
+        value: list.as_ref()
+    });
     recv!(&CachePutReply { succeeded } => {
         if !succeeded {
             artiq_raise!("CacheError", "cannot put into a busy cache row")
@@ -249,8 +238,8 @@ extern fn i2c_read(busno: i32, ack: bool) -> i32 {
 unsafe fn attribute_writeback(typeinfo: *const ()) {
     struct Attr {
         offset: usize,
-        tag:    *const u8,
-        name:   *const u8
+        tag:    CSlice<'static, u8>,
+        name:   CSlice<'static, u8>
     }
 
     struct Type {
@@ -276,7 +265,7 @@ unsafe fn attribute_writeback(typeinfo: *const ()) {
                 let attribute = *attributes;
                 attributes = attributes.offset(1);
 
-                if !(*attribute).tag.is_null() {
+                if (*attribute).tag.len() > 0 {
                     send_async_rpc(0, (*attribute).tag, [
                         &object as *const _ as *const (),
                         &(*attribute).name as *const _ as *const (),
diff --git a/artiq/firmware/liballoc_artiq/lib.rs b/artiq/firmware/liballoc_artiq/lib.rs
index 6e4278da4..073062973 100644
--- a/artiq/firmware/liballoc_artiq/lib.rs
+++ b/artiq/firmware/liballoc_artiq/lib.rs
@@ -1,5 +1,3 @@
-#![allow(dead_code)] // FIXME
-
 #![feature(allocator)]
 #![no_std]
 #![allocator]
diff --git a/artiq/firmware/libstd_artiq/lib.rs b/artiq/firmware/libstd_artiq/lib.rs
index 3a7f66404..9d6d7471d 100644
--- a/artiq/firmware/libstd_artiq/lib.rs
+++ b/artiq/firmware/libstd_artiq/lib.rs
@@ -1,4 +1,4 @@
-#![feature(lang_items, asm, alloc, collections, libc, needs_panic_runtime,
+#![feature(lang_items, asm, alloc, collections, needs_panic_runtime,
            unicode, raw, int_error_internals, try_from, macro_reexport,
            allow_internal_unstable, stmt_expr_attributes)]
 #![no_std]
@@ -9,7 +9,6 @@ extern crate alloc;
 #[macro_use]
 #[macro_reexport(vec, format)]
 extern crate collections;
-extern crate libc;
 
 pub use core::{any, cell, clone, cmp, convert, default, hash, iter, marker, mem, num,
     ops, option, ptr, result, sync,
diff --git a/artiq/firmware/runtime/Cargo.toml b/artiq/firmware/runtime/Cargo.toml
index e76b20478..3fe32e4ad 100644
--- a/artiq/firmware/runtime/Cargo.toml
+++ b/artiq/firmware/runtime/Cargo.toml
@@ -17,6 +17,7 @@ compiler_builtins = { git = "https://github.com/rust-lang-nursery/compiler-built
 alloc_artiq = { path = "../liballoc_artiq" }
 std_artiq = { path = "../libstd_artiq", features = ["alloc"] }
 logger_artiq = { path = "../liblogger_artiq" }
+cslice = { version = "0.3" }
 log = { version = "0.3", default-features = false, features = ["max_level_debug"] }
 board = { path = "../libboard", features = ["uart_console"] }
 fringe = { version = "= 1.1.0", default-features = false, features = ["alloc"] }
diff --git a/artiq/firmware/runtime/kernel_proto.rs b/artiq/firmware/runtime/kernel_proto.rs
index 5b3c11c34..f235c02ab 100644
--- a/artiq/firmware/runtime/kernel_proto.rs
+++ b/artiq/firmware/runtime/kernel_proto.rs
@@ -1,6 +1,5 @@
 #![allow(dead_code)]
 
-use core::marker::PhantomData;
 use core::fmt;
 
 pub const KERNELCPU_EXEC_ADDRESS:    usize = 0x40800000;
@@ -11,14 +10,13 @@ pub const KSUPPORT_HEADER_SIZE:      usize = 0x80;
 #[repr(C)]
 #[derive(Debug, Clone)]
 pub struct Exception<'a> {
-    pub name:     *const u8,
-    pub file:     *const u8,
+    pub name:     &'a str,
+    pub file:     &'a str,
     pub line:     u32,
     pub column:   u32,
-    pub function: *const u8,
-    pub message:  *const u8,
-    pub param:    [i64; 3],
-    pub phantom:  PhantomData<&'a str>
+    pub function: &'a str,
+    pub message:  &'a str,
+    pub param:    [i64; 3]
 }
 
 #[derive(Debug)]
diff --git a/artiq/firmware/runtime/lib.rs b/artiq/firmware/runtime/lib.rs
index 61ee29feb..d5292f9ad 100644
--- a/artiq/firmware/runtime/lib.rs
+++ b/artiq/firmware/runtime/lib.rs
@@ -6,6 +6,7 @@ extern crate alloc_artiq;
 #[macro_use]
 extern crate std_artiq as std;
 extern crate libc;
+extern crate cslice;
 #[macro_use]
 extern crate log;
 extern crate logger_artiq;
diff --git a/artiq/firmware/runtime/rpc_proto.rs b/artiq/firmware/runtime/rpc_proto.rs
index 493bcb3bc..83c716432 100644
--- a/artiq/firmware/runtime/rpc_proto.rs
+++ b/artiq/firmware/runtime/rpc_proto.rs
@@ -1,7 +1,8 @@
 #![allow(dead_code)]
 
-use core::slice;
+use core::str;
 use std::io::{self, Read, Write};
+use cslice::{CSlice, CMutSlice};
 use proto::*;
 use self::tag::{Tag, TagIterator, split_tag};
 
@@ -30,11 +31,10 @@ unsafe fn recv_value(reader: &mut Read, tag: Tag, data: &mut *mut (),
                 *ptr = read_u64(reader)?; Ok(())
             }),
         Tag::String => {
-            consume_value!(*mut u8, |ptr| {
-                let length = read_u32(reader)?;
-                // NB: the received string includes a trailing \0
-                *ptr = alloc(length as usize)? as *mut u8;
-                reader.read_exact(slice::from_raw_parts_mut(*ptr, length as usize))?;
+            consume_value!(CMutSlice<u8>, |ptr| {
+                let length = read_u32(reader)? as usize;
+                *ptr = CMutSlice::new(alloc(length)? as *mut u8, length);
+                reader.read_exact((*ptr).as_mut())?;
                 Ok(())
             })
         }
@@ -86,12 +86,6 @@ pub fn recv_return(reader: &mut Read, tag_bytes: &[u8], data: *mut (),
     Ok(())
 }
 
-pub unsafe fn from_c_str<'a>(ptr: *const u8) -> &'a str {
-    use core::{str, slice};
-    extern { fn strlen(ptr: *const u8) -> usize; }
-    str::from_utf8_unchecked(slice::from_raw_parts(ptr as *const u8, strlen(ptr)))
-}
-
 unsafe fn send_value(writer: &mut Write, tag: Tag, data: &mut *const ()) -> io::Result<()> {
     macro_rules! consume_value {
         ($ty:ty, |$ptr:ident| $map:expr) => ({
@@ -114,8 +108,8 @@ unsafe fn send_value(writer: &mut Write, tag: Tag, data: &mut *const ()) -> io::
             consume_value!(u64, |ptr|
                 write_u64(writer, *ptr)),
         Tag::String =>
-            consume_value!(*const u8, |ptr|
-                write_string(writer, from_c_str(*ptr))),
+            consume_value!(CSlice<u8>, |ptr|
+                write_string(writer, str::from_utf8_unchecked((*ptr).as_ref()))),
         Tag::Tuple(it, arity) => {
             let mut it = it.clone();
             write_u8(writer, arity)?;
@@ -145,9 +139,9 @@ unsafe fn send_value(writer: &mut Write, tag: Tag, data: &mut *const ()) -> io::
             Ok(())
         }
         Tag::Keyword(it) => {
-            struct Keyword { name: *const u8, contents: () };
+            struct Keyword<'a> { name: CSlice<'a, u8>, contents: () };
             consume_value!(Keyword, |ptr| {
-                write_string(writer, from_c_str((*ptr).name))?;
+                write_string(writer, str::from_utf8_unchecked((*ptr).name.as_ref()))?;
                 let tag = it.clone().next().expect("truncated tag");
                 let mut data = &(*ptr).contents as *const ();
                 send_value(writer, tag, &mut data)
diff --git a/artiq/firmware/runtime/session.rs b/artiq/firmware/runtime/session.rs
index 682dbae1c..106ed5412 100644
--- a/artiq/firmware/runtime/session.rs
+++ b/artiq/firmware/runtime/session.rs
@@ -62,8 +62,7 @@ struct Session<'a> {
     congress: &'a mut Congress,
     kernel_state: KernelState,
     watchdog_set: board::clock::WatchdogSet,
-    log_buffer: String,
-    interner: BTreeSet<String>
+    log_buffer: String
 }
 
 impl<'a> Session<'a> {
@@ -72,8 +71,7 @@ impl<'a> Session<'a> {
             congress: congress,
             kernel_state: KernelState::Absent,
             watchdog_set: board::clock::WatchdogSet::new(),
-            log_buffer: String::new(),
-            interner: BTreeSet::new()
+            log_buffer: String::new()
         }
     }
 
@@ -183,6 +181,7 @@ unsafe fn kern_load(io: &Io, session: &mut Session, library: &[u8]) -> io::Resul
                 Ok(())
             }
             &kern::LoadReply(Err(error)) => {
+                kernel::stop();
                 Err(io::Error::new(io::ErrorKind::Other,
                                    format!("cannot load kernel: {}", error)))
             }
@@ -332,22 +331,14 @@ fn process_host_message(io: &Io,
                 }
             })?;
 
-            // FIXME: gross.
-            fn into_c_str(interner: &mut BTreeSet<String>, s: String) -> *const u8 {
-                let s = s + "\0";
-                interner.insert(s.clone());
-                let p = interner.get(&s).unwrap().as_bytes().as_ptr();
-                p
-            }
             let exn = kern::Exception {
-                name: into_c_str(&mut session.interner, name),
-                message: into_c_str(&mut session.interner, message),
-                param: param,
-                file: into_c_str(&mut session.interner, file),
-                line: line,
-                column: column,
-                function: into_c_str(&mut session.interner, function),
-                phantom: ::core::marker::PhantomData
+                name:     name.as_ref(),
+                message:  message.as_ref(),
+                param:    param,
+                file:     file.as_ref(),
+                line:     line,
+                column:   column,
+                function: function.as_ref()
             };
             kern_send(io, &kern::RpcRecvReply(Err(exn)))?;
 
@@ -513,40 +504,33 @@ fn process_kern_message(io: &Io,
                 }
             }
 
-            &kern::RunException { exception: ref exn, backtrace } => {
+            &kern::RunException {
+                exception: kern::Exception { name, message, param, file, line, column, function },
+                backtrace
+            } => {
                 unsafe { kernel::stop() }
                 session.kernel_state = KernelState::Absent;
                 unsafe { session.congress.cache.unborrow() }
 
-                unsafe fn from_c_str<'a>(s: *const u8) -> &'a str {
-                    use ::libc::{c_char, size_t};
-                    use core::slice;
-                    extern { fn strlen(s: *const c_char) -> size_t; }
-                    let s = slice::from_raw_parts(s, strlen(s as *const c_char));
-                    str::from_utf8_unchecked(s)
-                }
-                let name = unsafe { from_c_str(exn.name) };
-                let message = unsafe { from_c_str(exn.message) };
-                let file = unsafe { from_c_str(exn.file) };
-                let function = unsafe { from_c_str(exn.function) };
                 match stream {
                     None => {
                         error!("exception in flash kernel");
-                        error!("{}: {} {:?}", name, message, exn.param);
-                        error!("at {}:{}:{} in {}", file, exn.line, exn.column, function);
+                        error!("{}: {} {:?}", name, message, param);
+                        error!("at {}:{}:{} in {}", file, line, column, function);
                         return Ok(true)
                     },
-                    Some(ref mut stream) =>
+                    Some(ref mut stream) => {
                         host_write(stream, host::Reply::KernelException {
-                            name: name,
-                            message: message,
-                            param: exn.param,
-                            file: file,
-                            line: exn.line,
-                            column: exn.column,
-                            function: function,
+                            name:      name,
+                            message:   message,
+                            param:     param,
+                            file:      file,
+                            line:      line,
+                            column:    column,
+                            function:  function,
                             backtrace: backtrace
                         })
+                    }
                 }
             }
 
diff --git a/artiq/runtime/artiq_personality.c b/artiq/runtime/artiq_personality.c
index 48dcf900d..510e3f9a1 100644
--- a/artiq/runtime/artiq_personality.c
+++ b/artiq/runtime/artiq_personality.c
@@ -230,18 +230,19 @@ static _Unwind_Reason_Code __artiq_uncaught_exception(
         void *stop_parameter);
 
 struct artiq_raised_exception {
-  struct _Unwind_Exception unwind;
-  struct artiq_exception artiq;
-  int handled;
+  struct    _Unwind_Exception unwind;
+  struct    artiq_exception artiq;
+  int       handled;
   uintptr_t backtrace[1024];
-  size_t backtrace_size;
+  size_t    backtrace_size;
 };
 
 static struct artiq_raised_exception inflight;
 
 void __artiq_raise(struct artiq_exception *artiq_exn) {
-  EH_LOG("===> raise (name=%s, msg=%s, params=[%lld,%lld,%lld])",
-         artiq_exn->name, artiq_exn->message,
+  EH_LOG("===> raise (name=%.*s, msg=%.*s, params=[%lld,%lld,%lld])",
+         (int)artiq_exn->name.len, (const char*)artiq_exn->name.ptr,
+         (int)artiq_exn->name.len, (const char*)artiq_exn->message.ptr,
          (long long int)artiq_exn->param[0],
          (long long int)artiq_exn->param[1],
          (long long int)artiq_exn->param[2]);
@@ -269,8 +270,6 @@ void __artiq_reraise() {
     __artiq_raise(&inflight.artiq);
   } else {
     EH_LOG0("===> resume");
-    EH_ASSERT((inflight.artiq.typeinfo != 0) &&
-              "Need an exception to reraise");
     _Unwind_Resume(&inflight.unwind);
     abort();
   }
@@ -333,8 +332,8 @@ _Unwind_Reason_Code __artiq_personality(
 
   struct artiq_raised_exception *inflight =
           (struct artiq_raised_exception*)exceptionObject;
-  EH_LOG("=> exception name=%s",
-         inflight->artiq.name);
+  EH_LOG("=> exception name=%.*s",
+         (int)inflight->artiq.name.len, (const char*)inflight->artiq.name.ptr);
 
   // Get a pointer to LSDA. If there's no LSDA, this function doesn't
   // actually handle any exceptions.
@@ -418,13 +417,17 @@ _Unwind_Reason_Code __artiq_personality(
           if(typeInfoOffset > 0) {
             unsigned encodingSize = getEncodingSize(ttypeEncoding);
             const uint8_t *typeInfoPtrPtr = classInfo - typeInfoOffset * encodingSize;
-            uintptr_t typeInfoPtr = readEncodedPointer(&typeInfoPtrPtr, ttypeEncoding);
+            const struct slice *typeInfoPtr =
+              (const struct slice *)readEncodedPointer(&typeInfoPtrPtr, ttypeEncoding);
             EH_LOG("encodingSize=%u typeInfoPtrPtr=%p typeInfoPtr=%p",
                    encodingSize, typeInfoPtrPtr, (void*)typeInfoPtr);
-            EH_LOG("typeInfo=%s", (char*)typeInfoPtr);
+            if(typeInfoPtr != NULL) {
+              EH_LOG("typeInfo=%.*s", (int)typeInfoPtr->len, (const char *)typeInfoPtr->ptr);
+            }
 
-            if(typeInfoPtr == 0 || !strcmp((char*)inflight->artiq.typeinfo,
-                                           (char*)typeInfoPtr)) {
+            if(typeInfoPtr == NULL ||
+                  (inflight->artiq.name.len == typeInfoPtr->len &&
+                  !memcmp(inflight->artiq.name.ptr, typeInfoPtr->ptr, typeInfoPtr->len))) {
               EH_LOG0("matching action found");
               exceptionMatched = 1;
               break;
diff --git a/artiq/runtime/artiq_personality.h b/artiq/runtime/artiq_personality.h
index 6f75ae2d8..4848e47c0 100644
--- a/artiq/runtime/artiq_personality.h
+++ b/artiq/runtime/artiq_personality.h
@@ -10,16 +10,13 @@ struct slice {
 };
 
 struct artiq_exception {
-  union {
-    uintptr_t typeinfo;
-    const char *name;
-  };
-  const char *file;
-  int32_t line;
-  int32_t column;
-  const char *function;
-  const char *message;
-  int64_t param[3];
+  struct slice name;
+  struct slice file;
+  int32_t      line;
+  int32_t      column;
+  struct slice function;
+  struct slice message;
+  int64_t      param[3];
 };
 
 #ifdef __cplusplus
@@ -32,20 +29,6 @@ void __artiq_raise(struct artiq_exception *artiq_exn)
 void __artiq_reraise(void)
         __attribute__((noreturn));
 
-#define artiq_raise_from_c(exnname, exnmsg, exnparam0, exnparam1, exnparam2) \
-        do { \
-          struct artiq_exception exn = { \
-            .name = "0:artiq.coredevice.exceptions." exnname, \
-            .message = exnmsg, \
-            .param = { exnparam0, exnparam1, exnparam2 }, \
-            .file = __FILE__, \
-            .line = __LINE__, \
-            .column = -1, \
-            .function = __func__, \
-          }; \
-          __artiq_raise(&exn); \
-        } while(0)
-
 /* Called by the runtime */
 void __artiq_terminate(struct artiq_exception *artiq_exn,
                        struct slice backtrace)
diff --git a/artiq/test/libartiq_support/artiq_terminate.c b/artiq/test/libartiq_support/artiq_terminate.c
index 36772f535..455566a42 100644
--- a/artiq/test/libartiq_support/artiq_terminate.c
+++ b/artiq/test/libartiq_support/artiq_terminate.c
@@ -9,11 +9,14 @@
 
 void __artiq_terminate(struct artiq_exception *exn,
                        struct slice backtrace) {
-  printf("Uncaught %s: %s (%"PRIi64", %"PRIi64", %"PRIi64")\n"
-         "at %s:%"PRIi32":%"PRIi32"\n",
-         exn->name, exn->message,
+  printf("Uncaught %.*s: %.*s (%"PRIi64", %"PRIi64", %"PRIi64")\n"
+         "at %.*s:%"PRIi32":%"PRIi32"\n",
+         (int)exn->name.len, (const char *)exn->name.ptr,
+         (int)exn->message.len, (const char *)exn->message.ptr,
          exn->param[0], exn->param[1], exn->param[1],
-         exn->file, exn->line, exn->column + 1);
+         (int)exn->file.len, (const char *)exn->file.ptr,
+         exn->line,
+         exn->column + 1);
 
   for(size_t i = 0; i < backtrace.len; i++) {
     printf("at %"PRIxPTR"\n", ((uintptr_t*)backtrace.ptr)[i]);
diff --git a/artiq/test/lit/integration/str.py b/artiq/test/lit/integration/str.py
index ab4e7866d..45b430d2a 100644
--- a/artiq/test/lit/integration/str.py
+++ b/artiq/test/lit/integration/str.py
@@ -1,4 +1,5 @@
 # RUN: %python -m artiq.compiler.testbench.jit %s
 # RUN: %python %s
 
+assert "xy" == "xy"
 assert ("x" + "y") == "xy"