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.

tool/build/lib/getargs.c

@@ -0,0 +1,171 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2021 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
+#include "libc/calls/calls.h"
+#include "libc/calls/struct/stat.h"
+#include "libc/errno.h"
+#include "libc/log/log.h"
+#include "libc/runtime/runtime.h"
+#include "libc/str/str.h"
+#include "libc/sysv/consts/map.h"
+#include "libc/sysv/consts/o.h"
+#include "libc/sysv/consts/prot.h"
+#include "libc/sysv/errfuns.h"
+#include "libc/x/x.h"
+#include "tool/build/lib/getargs.h"
+
+/**
+ * @fileoverview Fast Command Line Argument Ingestion.
+ *
+ * The purpose of this library is to be able to have build commands with
+ * huge argument lists. The way we do that is by replacing commands like
+ *
+ *     foo.com lots of args
+ *
+ * with this
+ *
+ *     echo of args >args
+ *     foo.com lots @args
+ *
+ * This iterator abstracts the process of reading the special `@`
+ * prefixed args. In order to do that quickly and easily, we make the
+ * following assumptions:
+ *
+ * 1. Arguments don't have whitespace.
+ * 2. Files have a trailing whitespace.
+ *
+ * We need (1) so GNU Make can go faster. Assume we tokenized based on
+ * newlines. We would would write that in our Makefile as follows:
+ *
+ *     # don't do this
+ *     target: thousands of args
+ *         $(file >$@.args) $(foreach x,$^,$(file >>$@.args,$(x)))
+ *         tool.com -o $@ @$@.args
+ *
+ * That is slow because it needs to open and close the args file
+ * thousands of times. If we trade away filenames with spaces then the
+ * following will only require a couple system calls:
+ *
+ *     # do this
+ *     target: thousands of args
+ *         $(file >$@.args,$^)
+ *         tool.com -o $@ @$@.args
+ *
+ * We need (2) because it make the code in this file simpler and avoids
+ * a malloc() dependency. Having that trailing character means argument
+ * parsing from files can be a zero-copy operation.
+ */
+
+#define IsSpace(c) ((255 & (c)) <= ' ')
+
+/**
+ * Zeroes GetArgs object and sets its fields.
+ * @param args is borrowed for the lifetime of the GetArgs object
+ */
+void getargs_init(struct GetArgs *ga, char **args) {
+  assert(args);
+  bzero(ga, sizeof(*ga));
+  ga->args = args;
+}
+
+/**
+ * Releases memory associated with GetArgs object and zeroes it.
+ */
+void getargs_destroy(struct GetArgs *ga) {
+  if (ga->map) munmap(ga->map, ga->mapsize);
+  bzero(ga, sizeof(*ga));
+}
+
+/**
+ * Gets next argument, e.g.
+ *
+ *     const char *s;
+ *     while ((s = getargs_next(&ga))) {
+ *       printf("%s\n", s);
+ *     }
+ *
+ * @return NUL-terminated string; it should not be freed; it should be
+ *     assumed that it stays in scope until the next getargs_next call
+ */
+const char *getargs_next(struct GetArgs *ga) {
+  int fd;
+  char *p;
+  size_t k;
+  unsigned m;
+  struct stat st;
+  do {
+    if (ga->map) {
+      for (; ga->j < ga->mapsize; ++ga->j) {
+        if (!IsSpace(ga->map[ga->j])) {
+          break;
+        }
+      }
+      k = 0;
+#if defined(__x86__) && defined(__GNUC__) && !defined(__STRICT_ANSI__)
+      typedef unsigned char xmm_t
+          __attribute__((__vector_size__(16), __aligned__(1)));
+      for (; ga->j + k + 16 <= ga->mapsize; k += 16) {
+        if ((m = __builtin_ia32_pmovmskb128(
+                     *(const xmm_t *)(ga->map + ga->j + k) >
+                     (xmm_t){' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ',
+                             ' ', ' ', ' ', ' ', ' ', ' '}) ^
+                 0xffff)) {
+          k += __builtin_ctzl(m);
+          break;
+        }
+      }
+#endif
+      for (; ga->j + k < ga->mapsize; ++k) {
+        if (IsSpace(ga->map[ga->j + k])) {
+          break;
+        }
+      }
+      if (k) {
+        if (ga->j + k < ga->mapsize) {
+          ga->map[ga->j + k] = 0;
+          p = ga->map + ga->j;
+          ga->j += ++k;
+          return p;
+        } else {
+          eio();
+          break;
+        }
+      }
+      if (munmap(ga->map, ga->mapsize) == -1) break;
+      ga->map = 0;
+      ga->mapsize = 0;
+      ga->j = 0;
+    }
+    if (!(p = ga->args[ga->i])) return 0;
+    ++ga->i;
+    if (*p != '@') return p;
+    ++p;
+    if ((fd = open((ga->path = p), O_RDONLY)) != -1) {
+      fstat(fd, &st);
+      if ((p = mmap(0, st.st_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd,
+                    0)) != MAP_FAILED) {
+        ga->map = p;
+        ga->mapsize = st.st_size;
+      }
+      close(fd);
+    }
+  } while (ga->map);
+  perror(ga->path);
+  exit(1);
+}