Add Linux ptrace() tutorial

libc/stdio/kvappendf.c

@@ -0,0 +1,68 @@
+/*-*- 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/intrin/kprintf.h"
+#include "libc/macros.internal.h"
+#include "libc/mem/mem.h"
+#include "libc/stdio/append.internal.h"
+
+#define W sizeof(size_t)
+
+/**
+ * Appends formatted string to buffer.
+ *
+ * This is an alternative to vappendf() that uses the kprintf()
+ * formatting facility. This has some advantages in terms of
+ * performance, code size, and memory safety. There's also
+ * disadvantages, such as lack of floating-point directives.
+ *
+ * @see kprintf()
+ */
+ssize_t kvappendf(char **b, const char *f, va_list v) {
+  char *p;
+  int r, s;
+  size_t n;
+  va_list w;
+  struct appendz z;
+  z = appendz((p = *b));
+  va_copy(w, v);
+  if ((r = kvsnprintf(p + z.i, z.n ? z.n - W - z.i : 0, f, v)) >= 0) {
+    n = ROUNDUP(z.i + r + 1, 8) + W;
+    if (n > z.n) {
+      if (!z.n) z.n = W * 2;
+      while (n > z.n) z.n += z.n >> 1;
+      z.n = ROUNDUP(z.n, W);
+      if ((p = realloc(p, z.n))) {
+        z.n = malloc_usable_size(p);
+        assert(!(z.n & (W - 1)));
+        s = kvsnprintf(p + z.i, z.n - W - z.i, f, w);
+        assert(s == r);
+        *b = p;
+      } else {
+        va_end(w);
+        return -1;
+      }
+    }
+    z.i += r;
+    if (!IsTiny() && W == 8) z.i |= (size_t)APPEND_COOKIE << 48;
+    *(size_t *)(p + z.n - W) = z.i;
+  }
+  va_end(w);
+  return r;
+}