Improve memory safety

This commit makes numerous refinements to cosmopolitan memory handling.

The default stack size has been reduced from 2mb to 128kb. A new macro
is now provided so you can easily reconfigure the stack size to be any
value you want. Work around the breaking change by adding to your main:

    STATIC_STACK_SIZE(0x00200000);  // 2mb stack

If you're not sure how much stack you need, then you can use:

    STATIC_YOINK("stack_usage_logging");

After which you can `sort -nr o/$MODE/stack.log`. Based on the unit test
suite, nothing in the Cosmopolitan repository (except for Python) needs
a stack size greater than 30kb. There are also new macros for detecting
the size and address of the stack at runtime, e.g. GetStackAddr(). We
also now support sigaltstack() so if you want to see nice looking crash
reports whenever a stack overflow happens, you can put this in main():

    ShowCrashReports();

Under `make MODE=dbg` and `make MODE=asan` the unit testing framework
will now automatically print backtraces of memory allocations when
things like memory leaks happen. Bugs are now fixed in ASAN global
variable overrun detection. The memtrack and asan runtimes also handle
edge cases now. The new tools helped to identify a few memory leaks,
which are fixed by this change.

This change should fix an issue reported in #288 with ARG_MAX limits.
Fixing this doubled the performance of MKDEPS.COM and AR.COM yet again.

libc/calls/commandv.c

@@ -18,39 +18,55 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/bits/safemacros.internal.h"
 #include "libc/calls/calls.h"
+#include "libc/log/libfatal.internal.h"
 #include "libc/runtime/runtime.h"
 #include "libc/str/str.h"
 #include "libc/sysv/errfuns.h"
 
-static noasan bool AccessCommand(char path[hasatleast PATH_MAX],
-                                 const char *name, size_t namelen,
-                                 size_t pathlen) {
-  if (pathlen + 1 + namelen + 1 + 4 + 1 > PATH_MAX) return -1;
-  if (pathlen && (path[pathlen - 1] != '/' && path[pathlen - 1] != '\\')) {
-    path[pathlen] = !IsWindows()                  ? '/'
-                    : memchr(path, '\\', pathlen) ? '\\'
-                                                  : '/';
-    pathlen++;
+static noasan bool EndsWithIgnoreCase(const char *p, size_t n, const char *s) {
+  size_t i, m;
+  m = __strlen(s);
+  if (n >= m) {
+    for (i = n - m; i < n; ++i) {
+      if (kToLower[p[i] & 255] != (*s++ & 255)) {
+        return false;
+      }
+    }
+    return true;
+  } else {
+    return false;
   }
-  memcpy(path + pathlen, name, namelen + 1);
-  if (isexecutable(path)) return true;
-  memcpy(path + pathlen + namelen, ".com", 5);
-  if (isexecutable(path)) return true;
-  memcpy(path + pathlen + namelen, ".exe", 5);
-  if (isexecutable(path)) return true;
-  return false;
 }
 
-static noasan bool SearchPath(char path[hasatleast PATH_MAX], const char *name,
-                              size_t namelen) {
+static noasan bool AccessCommand(const char *name,
+                                 char path[hasatleast PATH_MAX], size_t namelen,
+                                 const char *suffix, size_t pathlen) {
+  size_t suffixlen;
+  suffixlen = __strlen(suffix);
+  if (pathlen + 1 + namelen + suffixlen + 1 > PATH_MAX) return -1;
+  if (pathlen && (path[pathlen - 1] != '/' && path[pathlen - 1] != '\\')) {
+    path[pathlen] = !IsWindows()                    ? '/'
+                    : __memchr(path, '\\', pathlen) ? '\\'
+                                                    : '/';
+    pathlen++;
+  }
+  __repmovsb(path + pathlen, name, namelen);
+  __repmovsb(path + pathlen + namelen, suffix, suffixlen + 1);
+  return isexecutable(path);
+}
+
+static noasan bool SearchPath(const char *name, char path[hasatleast PATH_MAX],
+                              size_t namelen, const char *suffix) {
   size_t i;
   const char *p;
   p = firstnonnull(emptytonull(getenv("PATH")), "/bin:/usr/local/bin:/usr/bin");
   for (;;) {
     for (i = 0; p[i] && p[i] != ':' && p[i] != ';'; ++i) {
-      if (i < PATH_MAX) path[i] = p[i];
+      if (i < PATH_MAX) {
+        path[i] = p[i];
+      }
     }
-    if (AccessCommand(path, name, namelen, i)) {
+    if (AccessCommand(name, path, namelen, suffix, i)) {
       return true;
     }
     if (p[i] == ':' || p[i] == ';') {
@@ -62,6 +78,23 @@ static noasan bool SearchPath(char path[hasatleast PATH_MAX], const char *name,
   return false;
 }
 
+static noasan bool FindCommand(const char *name,
+                               char pathbuf[hasatleast PATH_MAX],
+                               size_t namelen, const char *suffix) {
+  if (memchr(name, '/', namelen) || memchr(name, '\\', namelen)) {
+    pathbuf[0] = 0;
+    return AccessCommand(name, pathbuf, namelen, suffix, 0);
+  }
+  return ((IsWindows() &&
+           (AccessCommand(name, pathbuf, namelen, suffix,
+                          stpcpy(pathbuf, kNtSystemDirectory) - pathbuf) ||
+            AccessCommand(name, pathbuf, namelen, suffix,
+                          stpcpy(pathbuf, kNtWindowsDirectory) - pathbuf) ||
+            AccessCommand(name, pathbuf, namelen, suffix,
+                          stpcpy(pathbuf, ".") - pathbuf))) ||
+          SearchPath(name, pathbuf, namelen, suffix));
+}
+
 /**
  * Resolves full pathname of executable.
  *
@@ -72,40 +105,28 @@ static noasan bool SearchPath(char path[hasatleast PATH_MAX], const char *name,
  * @vforksafe
  */
 noasan char *commandv(const char *name, char pathbuf[hasatleast PATH_MAX]) {
-  char *p;
+  int olderr;
   size_t namelen;
-  int rc, olderr;
   if (!name) {
     efault();
-    return NULL;
+    return 0;
   }
-  if (!(namelen = strlen(name))) {
+  if (!(namelen = __strlen(name))) {
     enoent();
-    return NULL;
+    return 0;
   }
   if (namelen + 1 > PATH_MAX) {
     enametoolong();
-    return NULL;
+    return 0;
   }
-  if (strchr(name, '/') || strchr(name, '\\')) {
-    if (AccessCommand(strcpy(pathbuf, ""), name, namelen, 0)) {
-      return pathbuf;
-    } else {
-      return NULL;
-    }
-  }
-  olderr = errno;
-  if ((IsWindows() &&
-       (AccessCommand(pathbuf, name, namelen,
-                      stpcpy(pathbuf, kNtSystemDirectory) - pathbuf) ||
-        AccessCommand(pathbuf, name, namelen,
-                      stpcpy(pathbuf, kNtWindowsDirectory) - pathbuf) ||
-        AccessCommand(pathbuf, name, namelen,
-                      stpcpy(pathbuf, ".") - pathbuf))) ||
-      SearchPath(pathbuf, name, namelen)) {
-    errno = olderr;
+  if (FindCommand(name, pathbuf, namelen, "") ||
+      (!EndsWithIgnoreCase(name, namelen, ".exe") &&
+       !EndsWithIgnoreCase(name, namelen, ".com") &&
+       !EndsWithIgnoreCase(name, namelen, ".com.dbg") &&
+       (FindCommand(name, pathbuf, namelen, ".com") ||
+        FindCommand(name, pathbuf, namelen, ".exe")))) {
     return pathbuf;
   } else {
-    return NULL;
+    return 0;
   }
 }