diff --git a/pydir/szbuild.py b/pydir/szbuild.py
new file mode 100755
index 0000000..8adc683
--- /dev/null
+++ b/pydir/szbuild.py
@@ -0,0 +1,239 @@
+#!/usr/bin/env python2
+
+import argparse
+import os
+import pipes
+import re
+import sys
+
+from utils import shellcmd
+from utils import FindBaseNaCl
+
+def BuildRegex(patterns, syms):
+    """Build a regular expression string for inclusion or exclusion.
+
+    Creates a regex string from an array of patterns and an array
+    of symbol names.  Each element in the patterns array is either a
+    regex, or a range of entries in the symbol name array, e.g. '2:9'.
+    """
+    pattern_list = []
+    for pattern in patterns:
+        if pattern[0].isdigit() or pattern[0] == ':':
+            # Legitimate symbols or regexes shouldn't start with a
+            # digit or a ':', so interpret the pattern as a range.
+            interval = pattern.split(':')
+            if len(interval) == 1:
+                # Treat singleton 'n' as 'n:n+1'.
+                lower = int(interval[0])
+                upper = lower + 1
+            elif len(interval) == 2:
+                # Handle 'a:b', 'a:', and ':b' with suitable defaults.
+                lower = int(interval[0]) if len(interval[0]) else 0
+                upper = int(interval[1]) if len(interval[1]) else len(syms)
+            else:
+                print 'Invalid range syntax: {p}'.format(p=pattern)
+                exit(1)
+            pattern = '$|^'.join([re.escape(p) for p in syms[lower:upper]])
+        pattern_list.append('^' + pattern + '$')
+    return '|'.join(pattern_list) if len(pattern_list) else '^$'
+
+def MatchSymbol(sym, re_include, re_exclude, default_match):
+    """Match a symbol name against inclusion/exclusion rules.
+
+    Returns True or False depending on whether the given symbol
+    matches the compiled include or exclude regexes.  The default is
+    returned if neither the include nor the exclude regex matches.
+    """
+    if re_exclude.match(sym):
+        # Always honor an explicit exclude before considering
+        # includes.
+        return False
+    if re_include.match(sym):
+        return True
+    return default_match
+
+def main():
+    """Create a hybrid translation from Subzero and llc.
+
+    Takes a finalized pexe and builds a native executable as a
+    hybrid of Subzero and llc translated bitcode.  Linker tricks are
+    used to determine whether Subzero or llc generated symbols are
+    used, on a per-symbol basis.
+
+    By default, for every symbol, its llc version is used.  Subzero
+    symbols can be enabled by regular expressions on the symbol name,
+    or by ranges of lines in this program's auto-generated symbol
+    file.
+
+    For each symbol, the --exclude arguments are first checked (the
+    symbol is 'rejected' on a match), followed by the --include
+    arguments (the symbol is 'accepted' on a match), followed by
+    unconditional 'rejection'.  The Subzero version is used for an
+    'accepted' symbol, and the llc version is used for a 'rejected'
+    symbol.
+
+    Each --include and --exclude argument can be a regular expression
+    or a range of lines in the symbol file.  Each regular expression
+    is wrapped inside '^$', so if you want a substring match on 'foo',
+    use '.*foo.*' instead.  Ranges use python-style 'first:last'
+    notation, so e.g. use '0:10' or ':10' for the first 10 lines of
+    the file, or '1' for the second line of the file.
+
+    The --init argument does first-time initialization for the pexe,
+    including creation of the Subzero symbol file that is implicitly
+    used in the --include and --exclude arguments.  It can be removed
+    from the command line for subsequent executions if the pexe
+    doesn't change.
+
+    This scripts augments PATH so that various PNaCl and LLVM tools
+    can be run.  These extra paths are within the native_client tree.
+    When changes are made to these tools, copy them this way:
+      cd native_client
+      toolchain_build/toolchain_build_pnacl.py llvm_i686_linux \\
+      --install=toolchain/linux_x86/pnacl_newlib
+    """
+    argparser = argparse.ArgumentParser(
+        description='    ' + main.__doc__,
+        formatter_class=argparse.RawTextHelpFormatter)
+    argparser.add_argument('pexe', help='Finalized pexe to translate')
+    argparser.add_argument('--init', dest='init', action='store_true',
+                           help='Perform first-time setup for the pexe')
+    argparser.add_argument('--include', '-i', default=[], dest='include',
+                           action='append',
+                           help='Subzero symbols to include ' +
+                                '(regex or line range)')
+    argparser.add_argument('--exclude', '-e', default=[], dest='exclude',
+                           action='append',
+                           help='Subzero symbols to exclude ' +
+                                '(regex or line range)')
+    argparser.add_argument('--output', '-o', default='a.out', dest='output',
+                           action='store',
+                           help='Output executable (default a.out)')
+    argparser.add_argument('-O', default='2', dest='optlevel',
+                           choices=['m1', '-1', '0', '1', '2'],
+                           help='Optimization level ' +
+                                '(m1 and -1 are equivalent)')
+    argparser.add_argument('--verbose', '-v', dest='verbose',
+                           action='store_true',
+                           help='Display some extra debugging output')
+    args = argparser.parse_args()
+
+    pexe = args.pexe
+    [pexe_base, ext] = os.path.splitext(pexe)
+    if ext != '.pexe':
+        pexe_base = pexe
+    pexe_base_unescaped = pexe_base
+    pexe_base = pipes.quote(pexe_base)
+    pexe = pipes.quote(pexe)
+    exe = args.output
+
+    nacl_root = FindBaseNaCl()
+    os.environ['PATH'] = (
+        '{root}/toolchain/linux_x86/pnacl_newlib/bin{sep}' +
+        '{root}/toolchain/linux_x86/pnacl_newlib/host_x86_32/bin{sep}' +
+        '{path}'
+        ).format(root=nacl_root, sep=os.pathsep, path=os.environ['PATH'])
+    obj_llc = pexe_base + '.llc.o'
+    obj_sz = pexe_base + '.sz.o'
+    asm_sz = pexe_base + '.sz.s'
+    obj_llc_weak = pexe_base + '.weak.llc.o'
+    obj_sz_weak = pexe_base + '.weak.sz.o'
+    obj_partial = pexe_base + '.o'
+    sym_llc = pexe_base + '.sym.llc.txt'
+    sym_sz = pexe_base + '.sym.sz.txt'
+    sym_sz_unescaped = pexe_base_unescaped + '.sym.sz.txt'
+    whitelist_sz = pexe_base + '.wl.sz.txt'
+    whitelist_sz_unescaped = pexe_base_unescaped + '.wl.sz.txt'
+
+    if args.init:
+        opt_level = args.optlevel
+        opt_level_map = { 'm1':'0', '-1':'0', '0':'0', '1':'1', '2':'2' }
+        shellcmd((
+            'pnacl-translate -ffunction-sections -c -arch x86-32-linux ' +
+            '-O{level} --pnacl-driver-append-LLC_FLAGS_EXTRA=-externalize ' +
+            '-o {obj} {pexe}'
+            ).format(level=opt_level_map[opt_level], obj=obj_llc, pexe=pexe),
+                 echo=args.verbose)
+        shellcmd((
+            'objcopy --redefine-sym _start=_user_start {obj}'
+            ).format(obj=obj_llc), echo=args.verbose)
+        shellcmd((
+            '{root}/toolchain_build/src/subzero/llvm2ice ' +
+            '-O{level} -bitcode-format=pnacl -disable-globals ' +
+            '-externalize -ffunction-sections {pexe} -o {asm}'
+            ).format(root=nacl_root,level=opt_level, pexe=pexe, asm=asm_sz),
+                 echo=args.verbose)
+        shellcmd((
+            'llvm-mc -arch=x86 -x86-asm-syntax=intel -filetype=obj -o {obj} ' +
+            '{asm}'
+            ).format(asm=asm_sz, obj=obj_sz), echo=args.verbose)
+        shellcmd((
+            'objcopy --redefine-sym _start=_user_start {obj}'
+            ).format(obj=obj_sz), echo=args.verbose)
+        shellcmd((
+            'nm {obj} | sed -n "s/.* [a-zA-Z] //p" > {sym}'
+            ).format(obj=obj_sz, sym=sym_sz), echo=args.verbose)
+        shellcmd((
+            'nm {obj} | sed -n "s/.* [a-zA-Z] //p" > {sym}'
+            ).format(obj=obj_llc, sym=sym_llc), echo=args.verbose)
+
+    with open(sym_sz_unescaped) as f:
+        sz_syms = f.read().splitlines()
+    re_include_str = BuildRegex(args.include, sz_syms)
+    re_exclude_str = BuildRegex(args.exclude, sz_syms)
+    re_include = re.compile(re_include_str)
+    re_exclude = re.compile(re_exclude_str)
+    # If a symbol doesn't explicitly match re_include or re_exclude,
+    # the default MatchSymbol() result is False, unless some --exclude
+    # args are provided and no --include args are provided.
+    default_match = len(args.exclude) and not len(args.include)
+
+    whitelist_has_items = False
+    with open(whitelist_sz_unescaped, 'w') as f:
+        for sym in sz_syms:
+            if MatchSymbol(sym, re_include, re_exclude, default_match):
+                f.write(sym + '\n')
+                whitelist_has_items = True
+    shellcmd((
+        'objcopy --weaken {obj} {weak}'
+        ).format(obj=obj_sz, weak=obj_sz_weak), echo=args.verbose)
+    if whitelist_has_items:
+        # objcopy returns an error if the --weaken-symbols file is empty.
+        shellcmd((
+            'objcopy --weaken-symbols={whitelist} {obj} {weak}'
+            ).format(whitelist=whitelist_sz, obj=obj_llc, weak=obj_llc_weak),
+                 echo=args.verbose)
+    else:
+        shellcmd((
+            'objcopy {obj} {weak}'
+            ).format(obj=obj_llc, weak=obj_llc_weak), echo=args.verbose)
+    shellcmd((
+        'ld -r -m elf_i386 -o {partial} {sz} {llc}'
+        ).format(partial=obj_partial, sz=obj_sz_weak, llc=obj_llc_weak),
+             echo=args.verbose)
+    shellcmd((
+        'objcopy -w --localize-symbol="*" {partial}'
+        ).format(partial=obj_partial), echo=args.verbose)
+    shellcmd((
+        'objcopy --globalize-symbol=_user_start {partial}'
+        ).format(partial=obj_partial), echo=args.verbose)
+    shellcmd((
+        'gcc -m32 {partial} -o {exe} ' +
+        # Keep the rest of this command line (except szrt.c) in sync
+        # with RunHostLD() in pnacl-translate.py.
+        '{root}/toolchain/linux_x86/pnacl_newlib/lib-x86-32-linux/' +
+        '{{unsandboxed_irt,irt_query_list}}.o ' +
+        '{root}/toolchain_build/src/subzero/runtime/szrt.c ' +
+        '-lpthread -lrt'
+        ).format(partial=obj_partial, exe=exe, root=nacl_root),
+             echo=args.verbose)
+    # Put the extra verbose printing at the end.
+    if args.verbose:
+        print 'PATH={path}'.format(path=os.environ['PATH'])
+        print 'include={regex}'.format(regex=re_include_str)
+        print 'exclude={regex}'.format(regex=re_exclude_str)
+        print 'default_match={dm}'.format(dm=default_match)
+        print 'Number of Subzero syms = {num}'.format(num=len(sz_syms))
+
+if __name__ == '__main__':
+    main()
diff --git a/runtime/szrt.c b/runtime/szrt.c
new file mode 100644
index 0000000..908c20e
--- /dev/null
+++ b/runtime/szrt.c
@@ -0,0 +1,77 @@
+//===- subzero/runtime/szrt.c - Subzero runtime source ----------*- C++ -*-===//
+//
+//                        The Subzero Code Generator
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the runtime helper routines that are needed by
+// Subzero.  This needs to be compiled by some non-Subzero compiler.
+//
+//===----------------------------------------------------------------------===//
+
+#include <stdint.h>
+#include <stdlib.h>
+
+void ice_unreachable(void) {
+  abort();
+}
+
+uint32_t cvtftoui32(float value) {
+  return (uint32_t) value;
+}
+
+uint32_t cvtdtoui32(double value) {
+  return (uint32_t) value;
+}
+
+int64_t cvtftosi64(float value) {
+  return (int64_t) value;
+}
+
+int64_t cvtdtosi64(double value) {
+  return (int64_t) value;
+}
+
+uint64_t cvtftoui64(float value) {
+  return (uint64_t) value;
+}
+
+uint64_t cvtdtoui64(double value) {
+  return (uint64_t) value;
+}
+
+float cvtui32tof(uint32_t value) {
+  return (float) value;
+}
+
+float cvtsi64tof(int64_t value) {
+  return (float) value;
+}
+
+float cvtui64tof(uint64_t value) {
+  return (float) value;
+}
+
+double cvtui32tod(uint32_t value) {
+  return (double) value;
+}
+
+double cvtsi64tod(int64_t value) {
+  return (double) value;
+}
+
+double cvtui64tod(uint64_t value) {
+  return (double) value;
+}
+
+/* TODO(stichnot):
+   Sz_fptoui_v4f32
+   Sz_uitofp_v4i32
+   Sz_bitcast_v8i1_to_i8
+   Sz_bitcast_v16i1_to_i16
+   Sz_bitcast_i8_to_v8i1
+   Sz_bitcast_i16_to_v16i1
+*/