diff --git a/Makefile b/Makefile
index fd1083b72..e9e61b85e 100644
--- a/Makefile
+++ b/Makefile
@@ -206,7 +206,7 @@ depend:	o/$(MODE)/depend
 tags:	TAGS HTAGS
 
 o/$(MODE)/.x:
-	@$(MKDIR) $(@D) && touch $@
+	@mkdir -p $(@D) && touch $@
 
 o/$(MODE)/srcs.txt: o/$(MODE)/.x $(MAKEFILES) $(call uniq,$(foreach x,$(SRCS),$(dir $(x))))
 	$(file >$@) $(foreach x,$(SRCS),$(file >>$@,$(x)))
diff --git a/build/bootstrap/compile.com b/build/bootstrap/compile.com
index ff0c7a674..8d185afef 100755
Binary files a/build/bootstrap/compile.com and b/build/bootstrap/compile.com differ
diff --git a/build/definitions.mk b/build/definitions.mk
index 32a8e11d1..96f22072b 100644
--- a/build/definitions.mk
+++ b/build/definitions.mk
@@ -46,11 +46,6 @@ V ?= 1
 LC_ALL = C
 SOURCE_DATE_EPOCH = 0
 
-DD ?= /bin/dd
-CP ?= /bin/cp -f
-RM ?= /bin/rm -f
-SED ?= /bin/sed
-MKDIR ?= /bin/mkdir -p
 TAGS ?= /usr/bin/ctags  # emacs source builds or something breaks it
 ARFLAGS = rcsD
 ZFLAGS ?=
@@ -83,41 +78,14 @@ PWD := $(shell pwd)
 IMAGE_BASE_VIRTUAL ?= 0x400000
 HELLO := $(shell build/hello)
 TMPDIR := $(shell build/findtmp)
-COMPILE := $(shell build/getcompile)
-CCVERSION := $(shell build/getccversion $(CC))
+COMPILE := $(shell build/getcompile) -V$(shell build/getccversion $(CC))
 
 export ADDR2LINE
-export CCVERSION
-export COMPILE
-export CP
-export DD
-export GZ
-export IMAGE_BASE_VIRTUAL
 export LC_ALL
-export LOGFMT
-export MKDIR
 export MODE
-export OBJDUMP
-export RM
-export SED
 export SOURCE_DATE_EPOCH
 export TMPDIR
 export V
-export ZFLAGS
-
-unexport COMPILER_PATH
-unexport CPATH
-unexport CPLUS_INCLUDE_PATH
-unexport C_INCLUDE_PATH
-unexport DEPENDENCIES_OUTPUT
-unexport GCC_COMPARE_DEBUG
-unexport GCC_EXEC_PREFIX
-unexport LANG
-unexport LC_CTYPE
-unexport LC_MESSAGES
-unexport LIBRARY_PATH
-unexport OBJC_INCLUDE_PATH
-unexport SUNPRO_DEPENDENCIES
 
 FTRACE =								\
 	-pg
diff --git a/examples/examples.mk b/examples/examples.mk
index 1374b63a4..c011a62aa 100644
--- a/examples/examples.mk
+++ b/examples/examples.mk
@@ -130,7 +130,7 @@ o/$(MODE)/examples/nesemu1.com.dbg:				\
 $(EXAMPLES_OBJS): examples/examples.mk
 
 usr/share/dict/words: usr/share/dict/words.gz
-	@$(MKDIR) $(dir $@)
+	@mkdir -p $(@D)
 	@$(GZ) $(ZFLAGS) -d <$< >$@
 
 .PHONY: o/$(MODE)/examples
diff --git a/libc/runtime/exit.c b/libc/runtime/exit.c
index 694bc000e..6cfa3cdd9 100644
--- a/libc/runtime/exit.c
+++ b/libc/runtime/exit.c
@@ -39,8 +39,8 @@ wontreturn void exit(int exitcode) {
   if (weaken(__cxa_finalize)) {
     weaken(__cxa_finalize)(NULL);
   }
-  for (p = *weaken(__fini_array_end); p-- > *weaken(__fini_array_start);) {
-    ((void (*)(void))p)();
+  for (p = *weaken(__fini_array_end); p > *weaken(__fini_array_start);) {
+    ((void (*)(void))(*--p))();
   }
   _Exit(exitcode);
 }
diff --git a/libc/runtime/finddebugbinary.c b/libc/runtime/finddebugbinary.c
index 29dc83e65..3b5a37d85 100644
--- a/libc/runtime/finddebugbinary.c
+++ b/libc/runtime/finddebugbinary.c
@@ -35,7 +35,9 @@ const char *FindDebugBinary(void) {
   unsigned i, len;
   char buf[2][PATH_MAX];
   static char res[PATH_MAX];
-  const char *bins[4], *pwd;
+  const char *bins[4], *pwd, *comdbg;
+  if (res[0]) return res;
+  if ((comdbg = emptytonull(getenv("COMDBG")))) return comdbg;
   if (res[0]) return res;
   bins[0] = program_invocation_name;
   bins[1] = (const char *)getauxval(AT_EXECFN);
diff --git a/tool/build/compile.c b/tool/build/compile.c
index 92bfb75c4..d7c1023f3 100644
--- a/tool/build/compile.c
+++ b/tool/build/compile.c
@@ -63,12 +63,13 @@ FLAGS\n\
 \n\
   -A ACTION    specifies short command name for V=0 logging\n\
   -T TARGET    specifies target name for V=0 logging\n\
+  -V NUMBER    specifies compiler version\n\
   -t           touch target on success\n\
   -n           do nothing (used to prime the executable)\n\
   -?           print help\n\
 \n"
 
-struct Flags {
+struct Args {
   size_t n;
   char **p;
 };
@@ -92,6 +93,7 @@ bool wantubsan;
 bool touchtarget;
 
 char *cmd;
+char *comdbg;
 char *cachedcmd;
 char *originalcmd;
 char *colorflag;
@@ -106,9 +108,18 @@ int columns;
 sigset_t mask;
 sigset_t savemask;
 
-struct Flags flags;
+struct Args env;
+struct Args args;
 struct Command command;
 
+const char *const kSafeEnv[] = {
+    "ADDR2LINE",  // needed by GetAddr2linePath
+    "MAKEFLAGS",  // needed by IsRunningUnderMake
+    "PWD",        // just seems plain needed
+    "TERM",       // needed by IsTerminalInarticulate
+    "TMPDIR",     // needed by compiler
+};
+
 const char *const kGccOnlyFlags[] = {
     "--nocompress-debug-sections",
     "--noexecstack",
@@ -173,6 +184,27 @@ char *DescribeCommand(void) {
   return basename(cmd);
 }
 
+bool IsSafeEnv(const char *s) {
+  const char *p;
+  int n, m, l, r, x;
+  p = strchr(s, '=');
+  n = p ? p - s : -1;
+  l = 0;
+  r = ARRAYLEN(kSafeEnv) - 1;
+  while (l <= r) {
+    m = (l + r) >> 1;
+    x = strncmp(s, kSafeEnv[m], n);
+    if (x < 0) {
+      r = m - 1;
+    } else if (x > 0) {
+      l = m + 1;
+    } else {
+      return true;
+    }
+  }
+  return false;
+}
+
 bool IsGccOnlyFlag(const char *s) {
   int m, l, r, x;
   l = 0;
@@ -201,10 +233,24 @@ bool IsGccOnlyFlag(const char *s) {
   return false;
 }
 
-void AddFlag(char *s) {
+bool FileExistsAndIsNewerThan(const char *filepath, const char *thanpath) {
+  struct stat st1, st2;
+  if (stat(filepath, &st1) == -1) return false;
+  if (stat(thanpath, &st2) == -1) return false;
+  if (st1.st_mtim.tv_sec < st2.st_mtim.tv_sec) return false;
+  if (st1.st_mtim.tv_sec > st2.st_mtim.tv_sec) return true;
+  return st1.st_mtim.tv_nsec >= st2.st_mtim.tv_nsec;
+}
+
+void AddEnv(char *s) {
+  env.p = realloc(env.p, ++env.n * sizeof(*env.p));
+  env.p[env.n - 1] = s;
+}
+
+void AddArg(char *s) {
   size_t n;
-  flags.p = realloc(flags.p, ++flags.n * sizeof(*flags.p));
-  flags.p[flags.n - 1] = s;
+  args.p = realloc(args.p, ++args.n * sizeof(*args.p));
+  args.p[args.n - 1] = s;
   if (s) {
     n = strlen(s);
     if (command.n) {
@@ -229,7 +275,7 @@ int Launch(void) {
   if ((pid = vfork()) == -1) exit(errno);
   if (!pid) {
     sigprocmask(SIG_SETMASK, &savemask, NULL);
-    execv(cmd, flags.p);
+    execve(cmd, args.p, env.p);
     _exit(127);
   }
   while (waitpid(pid, &ws, 0) == -1) {
@@ -239,14 +285,14 @@ int Launch(void) {
 }
 
 int main(int argc, char *argv[]) {
-  char *p;
   size_t n;
+  char *p, **envp;
   int i, ws, rc, opt;
 
   /*
    * parse prefix arguments
    */
-  while ((opt = getopt(argc, argv, "?hntA:T:")) != -1) {
+  while ((opt = getopt(argc, argv, "?hntA:T:V:")) != -1) {
     switch (opt) {
       case 'n':
         exit(0);
@@ -259,6 +305,9 @@ int main(int argc, char *argv[]) {
       case 'T':
         target = optarg;
         break;
+      case 'V':
+        ccversion = atoi(optarg);
+        break;
       case '?':
       case 'h':
         write(1, MANUAL, sizeof(MANUAL) - 1);
@@ -278,39 +327,38 @@ int main(int argc, char *argv[]) {
     if (!(cmd = commandv(cmd, ccpath))) exit(127);
   }
 
-  ccversion = atoi(firstnonnull(emptytonull(getenv("CCVERSION")), "4"));
   isgcc = !!strstr(basename(cmd), "gcc");
   isclang = !!strstr(basename(cmd), "clang");
   iscc = isgcc | isclang;
 
   /*
-   * ingest flag arguments
+   * ingest arguments
    */
   for (i = optind; i < argc; ++i) {
     if (argv[i][0] != '-') {
-      AddFlag(argv[i]);
+      AddArg(argv[i]);
       continue;
     }
     if (!strcmp(argv[i], "-o")) {
-      AddFlag(argv[i]);
-      AddFlag((outpath = argv[++i]));
+      AddArg(argv[i]);
+      AddArg((outpath = argv[++i]));
       continue;
     }
     if (!iscc) {
-      AddFlag(argv[i]);
+      AddArg(argv[i]);
       continue;
     }
     if (isclang && IsGccOnlyFlag(argv[i])) {
       continue;
     }
     if (!strcmp(argv[i], "-w")) {
-      AddFlag(argv[i]);
-      AddFlag("-D__W__");
+      AddArg(argv[i]);
+      AddArg("-D__W__");
     } else if (!strcmp(argv[i], "-Oz")) {
       if (isclang) {
-        AddFlag(argv[i]);
+        AddArg(argv[i]);
       } else {
-        AddFlag("-Os");
+        AddArg("-Os");
       }
     } else if (!strcmp(argv[i], "-pg")) {
       wantpg = true;
@@ -328,17 +376,17 @@ int main(int argc, char *argv[]) {
       wantframe = false;
     } else if (!strcmp(argv[i], "-mno-vzeroupper")) {
       if (isgcc) {
-        AddFlag("-Wa,-msse2avx");
-        AddFlag("-D__MNO_VZEROUPPER__");
+        AddArg("-Wa,-msse2avx");
+        AddArg("-D__MNO_VZEROUPPER__");
       } else if (isclang) {
-        AddFlag("-mllvm");
-        AddFlag("-x86-use-vzeroupper=0");
+        AddArg("-mllvm");
+        AddArg("-x86-use-vzeroupper=0");
       }
     } else if (!strcmp(argv[i], "-msse2avx")) {
       if (isgcc) {
-        AddFlag(argv[i]);
+        AddArg(argv[i]);
       } else if (isclang) {
-        AddFlag("-Wa,-msse2avx");
+        AddArg("-Wa,-msse2avx");
       }
     } else if (!strcmp(argv[i], "-fsanitize=address")) {
       if (isgcc && ccversion >= 6) wantasan = true;
@@ -353,7 +401,7 @@ int main(int argc, char *argv[]) {
       wantubsan = false;
     } else if (startswith(argv[i], "-fsanitize=implicit") &&
                strstr(argv[i], "integer")) {
-      if (isgcc) AddFlag(argv[i]);
+      if (isgcc) AddArg(argv[i]);
     } else if (startswith(argv[i], "-fvect-cost") ||
                startswith(argv[i], "-mstringop") ||
                startswith(argv[i], "-gz") ||
@@ -362,18 +410,18 @@ int main(int argc, char *argv[]) {
                startswith(argv[i], "-fvect-cost") ||
                startswith(argv[i], "-fvect-cost")) {
       if (isgcc && ccversion >= 6) {
-        AddFlag(argv[i]);
+        AddArg(argv[i]);
       }
     } else if (startswith(argv[i], "-fdiagnostic-color=")) {
       colorflag = argv[i];
     } else if (startswith(argv[i], "-R") ||
                !strcmp(argv[i], "-fsave-optimization-record")) {
-      if (isclang) AddFlag(argv[i]);
+      if (isclang) AddArg(argv[i]);
     } else if (isclang && startswith(argv[i], "--debug-prefix-map")) {
       /* llvm doesn't provide a gas interface so simulate w/ clang */
-      AddFlag(xasprintf("-f%s", argv[i] + 2));
+      AddArg(xasprintf("-f%s", argv[i] + 2));
     } else {
-      AddFlag(argv[i]);
+      AddArg(argv[i]);
     }
   }
   if (!outpath) {
@@ -381,51 +429,62 @@ int main(int argc, char *argv[]) {
   }
 
   /*
-   * append special flags
+   * append special args
    */
   if (iscc) {
     if (isclang) {
-      /* AddFlag("-fno-integrated-as"); */
-      AddFlag("-Wno-unused-command-line-argument");
-      AddFlag("-Wno-incompatible-pointer-types-discards-qualifiers");
+      /* AddArg("-fno-integrated-as"); */
+      AddArg("-Wno-unused-command-line-argument");
+      AddArg("-Wno-incompatible-pointer-types-discards-qualifiers");
     }
-    AddFlag("-no-canonical-prefixes");
+    AddArg("-no-canonical-prefixes");
     if (!IsTerminalInarticulate()) {
-      AddFlag(firstnonnull(colorflag, "-fdiagnostics-color=always"));
+      AddArg(firstnonnull(colorflag, "-fdiagnostics-color=always"));
     }
     if (wantpg && !wantnopg) {
-      AddFlag("-pg");
-      AddFlag("-D__PG__");
+      AddArg("-pg");
+      AddArg("-D__PG__");
       if (wantnop && !isclang) {
-        AddFlag("-mnop-mcount");
-        AddFlag("-D__MNOP_MCOUNT__");
+        AddArg("-mnop-mcount");
+        AddArg("-D__MNOP_MCOUNT__");
       }
       if (wantrecord) {
-        AddFlag("-mrecord-mcount");
-        AddFlag("-D__MRECORD_MCOUNT__");
+        AddArg("-mrecord-mcount");
+        AddArg("-D__MRECORD_MCOUNT__");
       }
       if (wantfentry) {
-        AddFlag("-mfentry");
-        AddFlag("-D__MFENTRY__");
+        AddArg("-mfentry");
+        AddArg("-D__MFENTRY__");
       }
     }
     if (wantasan) {
-      AddFlag("-fsanitize=address");
-      AddFlag("-D__FSANITIZE_ADDRESS__");
+      AddArg("-fsanitize=address");
+      AddArg("-D__FSANITIZE_ADDRESS__");
     }
     if (wantubsan) {
-      AddFlag("-fsanitize=undefined");
-      AddFlag("-fno-data-sections");
+      AddArg("-fsanitize=undefined");
+      AddArg("-fno-data-sections");
     }
     if (wantframe) {
-      AddFlag("-fno-omit-frame-pointer");
+      AddArg("-fno-omit-frame-pointer");
     }
   }
 
   /*
-   * terminate argument list passed to subprocess
+   * terminate args
    */
-  AddFlag(NULL);
+  AddArg(NULL);
+
+  /*
+   * scrub environment for determinism and great justice
+   */
+  for (envp = environ; *envp; ++envp) {
+    if (IsSafeEnv(*envp)) {
+      AddEnv(*envp);
+    }
+  }
+  AddEnv("LC_ALL=C");
+  AddEnv("SOURCE_DATE_EPOCH=0");
 
   /*
    * ensure output directory exists
@@ -463,10 +522,15 @@ int main(int argc, char *argv[]) {
 
   /*
    * create temporary copy when launching APE binaries
+   * and we help FindDebugBinary to find debug symbols
    */
   if (!IsWindows() && endswith(cmd, ".com")) {
+    comdbg = xasprintf("%s.dbg", cmd);
     cachedcmd = xasprintf("o/%s", cmd);
-    if (fileexists(cachedcmd)) {
+    if (fileexists(comdbg)) {
+      AddEnv(xasprintf("COMDBG=%s", comdbg));
+    }
+    if (FileExistsAndIsNewerThan(cachedcmd, cmd)) {
       cmd = cachedcmd;
     } else {
       if (startswith(cmd, "o/")) {
@@ -478,6 +542,11 @@ int main(int argc, char *argv[]) {
     }
   }
 
+  /*
+   * terminate environment
+   */
+  AddEnv(NULL);
+
   /*
    * launch command
    */
diff --git a/tool/build/package.c b/tool/build/package.c
index ce8742be5..9d9671aa9 100644
--- a/tool/build/package.c
+++ b/tool/build/package.c
@@ -351,8 +351,10 @@ void OpenObject(struct Package *pkg, struct Object *obj, int mode, int prot,
   CHECK_NE(-1, (fd = open(&pkg->strings.p[obj->path], (obj->mode = mode))),
            "path=%`'s", &pkg->strings.p[obj->path]);
   CHECK_NE(-1, fstat(fd, &st));
-  CHECK_NE(MAP_FAILED, (obj->elf = mmap(NULL, (obj->size = st.st_size), prot,
-                                        flags, fd, 0)));
+  CHECK_NE(
+      MAP_FAILED,
+      (obj->elf = mmap(NULL, (obj->size = st.st_size), prot, flags, fd, 0)),
+      "path=%`'s", &pkg->strings.p[obj->path]);
   CHECK_NE(-1, close(fd));
   CHECK(IsElf64Binary(obj->elf, obj->size), "path=%`'s",
         &pkg->strings.p[obj->path]);