Remove _Hide keyword

It never did anything and isn't worthwhile as documentation.

libc/runtime/morph.c

@@ -0,0 +1,107 @@
+/*-*- 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 2022 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.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#define ShouldUseMsabiAttribute() 1
+#include "ape/sections.internal.h"
+#include "libc/dce.h"
+#include "libc/errno.h"
+#include "libc/intrin/asmflag.h"
+#include "libc/intrin/kprintf.h"
+#include "libc/nt/enum/pageflags.h"
+#include "libc/nt/memory.h"
+#include "libc/nt/thunk/msabi.h"
+#include "libc/runtime/runtime.h"
+#include "libc/sysv/consts/nr.h"
+#include "libc/sysv/consts/prot.h"
+
+__msabi extern typeof(VirtualProtect) *const __imp_VirtualProtect;
+
+__funline void __morph_mprotect(void *addr, size_t size, int prot, int ntprot) {
+#ifdef __x86_64__
+  bool cf;
+  int ax, dx;
+  uint32_t op;
+  if (!IsWindows()) {
+    asm volatile(CFLAG_ASM("clc\n\t"
+                           "syscall")
+                 : CFLAG_CONSTRAINT(cf), "=a"(ax), "=d"(dx)
+                 : "1"(__NR_mprotect), "D"(addr), "S"(size), "2"(prot)
+                 : "rcx", "r8", "r9", "r10", "r11", "memory");
+#ifndef NDEBUG
+    if (cf) ax = -ax;
+    if (ax == -EPERM) {
+      kprintf("error: need pledge(prot_exec) permission to code morph\n");
+    }
+    if (ax < 0) {
+      kprintf("error: __morph_mprotect(%p, %#zx, %d) failed: errno=%d\n", addr,
+              size, prot, -ax);
+    }
+#endif
+  } else {
+    __imp_VirtualProtect(addr, size, ntprot, &op);
+  }
+#elif defined(__aarch64__)
+  register long r0 asm("x0") = (long)addr;
+  register long r1 asm("x1") = (long)size;
+  register long r2 asm("x2") = (long)prot;
+  register long r8 asm("x8") = (long)__NR_mprotect;
+  register long r16 asm("x16") = (long)__NR_mprotect;
+  asm volatile("svc\t0"
+               : "+r"(r0)
+               : "r"(r1), "r"(r2), "r"(r8), "r"(r16)
+               : "memory");
+#endif
+}
+
+/**
+ * Begins code morphing executable.
+ *
+ * The following example
+ *
+ *     #include <cosmo.h>
+ *     #include <stdlib.h>
+ *
+ *     privileged int main() {  // privileged code is unmodifiable
+ *       ShowCrashReports();    // print report if trapped
+ *       __morph_begin(0);      // make executable code R+W
+ *       *(char *)exit = 0xCC;  // turn exit() into an INT3 trap
+ *       __morph_end();         // make executable code R+X
+ *       exit(0);               // won't actually exit
+ *     }
+ *
+ * shows how the exit() function can be recompiled at runtime to become
+ * an int3 (x86-64) debugger trap. What makes it tricky is Cosmopolitan
+ * maintains a R^X invariant, in order to support OpenBSD. So when code
+ * wants to modify some part of the executable image in memory the vast
+ * majority of the code stops being executable during that time, unless
+ * it's been linked into a special privileged section of the binary. It
+ * is only possible to code morph from privileged functions. Privileged
+ * functions are also only allowed to call other privileged functions.
+ */
+privileged void __morph_begin(void) {
+  __morph_mprotect(__executable_start, __privileged_start - __executable_start,
+                   PROT_READ | PROT_WRITE, kNtPageWritecopy);
+}
+
+/**
+ * Finishes code morphing executable.
+ */
+privileged void __morph_end(void) {
+  __morph_mprotect(__executable_start, __privileged_start - __executable_start,
+                   PROT_READ | PROT_EXEC, kNtPageExecuteRead);
+}