Make some systemic improvements

- add vdso dump utility - tests now log stack usage - rename g_ftrace to __ftrace - make internal spinlocks go faster - add conformant c11 atomics library - function tracing now logs stack usage - make function call tracing thread safe - add -X unsecure (no ssl) mode to redbean - munmap() has more consistent behavior now - pacify fsync() calls on python unit tests - make --strace flag work better in redbean - start minimizing and documenting compiler flags
2025-07-27 21:10:29 +00:00 · 2022-05-18 16:41:29 -07:00 · 2022-05-18 16:41:29 -07:00 · 9208c83f7a
commit 9208c83f7a
parent c6bbca55e9
141 changed files with 1948 additions and 1411 deletions
--- a/tool/args/args.c
+++ b/tool/args/args.c
@ -29,7 +29,7 @@
 STATIC_YOINK("zip_uri_support");

 static struct ZipArgs {
-  bool registered;
+  bool initialized;
  bool loaded;
  int oldargc;
  char *data;
@ -76,15 +76,15 @@ int LoadZipArgsImpl(int *argc, char ***argv, char *data) {
      start = 0;
    }
    if (founddots || *argc <= 1) {
-      if (!g_zipargs.registered) {
+      if (!g_zipargs.initialized) {
        atexit(FreeZipArgs);
-        g_zipargs.registered = true;
+        g_zipargs.oldargc = __argc;
+        g_zipargs.oldargv = __argv;
+        g_zipargs.initialized = true;
      }
      g_zipargs.loaded = true;
      g_zipargs.data = data;
      g_zipargs.args = args;
-      g_zipargs.oldargc = *argc;
-      g_zipargs.oldargv = *argv;
      *argc = n;
      *argv = args;
      __argc = n;
--- a/tool/emacs/cosmo-c-keywords.el
+++ b/tool/emacs/cosmo-c-keywords.el
@ -99,7 +99,8 @@
           "_Vector_size"))

        (gnu
-         '("__inline"
+         '("__extension__"
+           "__inline"
           "__thread"
           "__alignof"
           "__typeof"
--- a/tool/net/counters.inc
+++ b/tool/net/counters.inc
@ -1,4 +1,5 @@
 C(accepterrors)
+C(acceptflakes)
 C(acceptinterrupts)
 C(acceptresets)
 C(badlengths)
@ -74,6 +75,7 @@ C(sslunknownca)
 C(sslunknowncert)
 C(sslupgrades)
 C(sslverifyfailed)
+C(stackuse)
 C(statfails)
 C(staticrequests)
 C(stats)
--- a/tool/net/help.txt
+++ b/tool/net/help.txt
@ -54,6 +54,7 @@ FLAGS
  -Z        log worker system calls
  -f        log worker function calls
  -B        only use stronger cryptography
+  -X        disable ssl server and client support
  -s        increase silence                  [repeatable]
  -v        increase verbosity                [repeatable]
  -V        increase ssl verbosity            [repeatable]
@ -1980,13 +1981,15 @@ UNIX MODULE

    Makes directories.

+    Unlike mkdir() this convenience wrapper will automatically create
+    parent parent directories as needed. If the directory already exists
+    then, unlike mkdir() which returns EEXIST, the makedirs() function
+    will return success.
+
    `path` is the path of the directory you wish to create.

    `mode` is octal permission bits, e.g. `0755`.

-    Unlike mkdir() this convenience wrapper will automatically create
-    parent parent directories as needed.
-
  unix.chdir(path:str)
      ├─→ true
      └─→ nil, unix.Errno
--- a/tool/net/redbean.c
+++ b/tool/net/redbean.c
@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "dsp/scale/cdecimate2xuint8x8.h"
+#include "libc/bits/atomic.h"
 #include "libc/bits/bits.h"
 #include "libc/bits/likely.h"
 #include "libc/bits/popcnt.h"
@ -204,34 +205,26 @@ STATIC_YOINK("zip_uri_support");
 #define HeaderEqualCase(H, S) \
  SlicesEqualCase(S, strlen(S), HeaderData(H), HeaderLength(H))

-#define TRACE_BEGIN                                         \
-  do {                                                      \
-    if (!IsTiny()) {                                        \
-      if (funtrace) {                                       \
-        __atomic_fetch_add(&g_ftrace, 1, __ATOMIC_RELAXED); \
-      }                                                     \
-      if (systrace) {                                       \
-        __atomic_fetch_add(&__strace, 1, __ATOMIC_RELAXED); \
-      }                                                     \
-    }                                                       \
+#define TRACE_BEGIN             \
+  do {                          \
+    if (!IsTiny()) {            \
+      if (funtrace) ++__ftrace; \
+      if (systrace) ++__strace; \
+    }                           \
  } while (0)

-#define TRACE_END                                           \
-  do {                                                      \
-    if (!IsTiny()) {                                        \
-      if (funtrace) {                                       \
-        __atomic_fetch_sub(&g_ftrace, 1, __ATOMIC_RELAXED); \
-      }                                                     \
-      if (systrace) {                                       \
-        __atomic_fetch_sub(&__strace, 1, __ATOMIC_RELAXED); \
-      }                                                     \
-    }                                                       \
+#define TRACE_END               \
+  do {                          \
+    if (!IsTiny()) {            \
+      if (funtrace) --__ftrace; \
+      if (systrace) --__strace; \
+    }                           \
  } while (0)

-// letters not used: EIJNOQXYnoqwxy
+// letters not used: EIJNOQYnoqwxy
 // digits not used:  0123456789
 // puncts not used:  !"#$%&'()*+,-./;<=>@[\]^_`{|}~
-#define GETOPTS "BSVZabdfghijkmsuvzA:C:D:F:G:H:K:L:M:P:R:T:U:W:c:e:l:p:r:t:"
+#define GETOPTS "BSVXZabdfghijkmsuvzA:C:D:F:G:H:K:L:M:P:R:T:U:W:c:e:l:p:r:t:"

 extern unsigned long long __kbirth;

@ -403,6 +396,7 @@ static bool branded;
 static bool funtrace;
 static bool systrace;
 static bool meltdown;
+static bool unsecure;
 static bool printport;
 static bool daemonize;
 static bool logrusage;
@ -425,7 +419,6 @@ static bool sslclientverify;
 static bool connectionclose;
 static bool hasonworkerstop;
 static bool isexitingworker;
-static bool terminatemonitor;
 static bool hasonworkerstart;
 static bool leakcrashreports;
 static bool hasonhttprequest;
@ -437,6 +430,7 @@ static bool loggednetworkorigin;
 static bool ishandlingconnection;
 static bool hasonclientconnection;
 static bool evadedragnetsurveillance;
+static _Atomic(bool) terminatemonitor;

 static int zfd;
 static int frags;
@ -1213,7 +1207,7 @@ static void CallSimpleHookIfDefined(const char *s) {

 static void ReportWorkerExit(int pid, int ws) {
  int workers;
-  workers = __atomic_sub_fetch(&shared->workers, 1, __ATOMIC_SEQ_CST);
+  workers = atomic_fetch_sub(&shared->workers, 1) - 1;
  if (WIFEXITED(ws)) {
    if (WEXITSTATUS(ws)) {
      LockInc(&shared->c.failedchildren);
@ -3696,6 +3690,7 @@ static int LuaStoreAsset(lua_State *L) {

 static void ReseedRng(mbedtls_ctr_drbg_context *r, const char *s) {
 #ifndef UNSECURE
+  if (unsecure) return;
  CHECK_EQ(0, mbedtls_ctr_drbg_reseed(r, (void *)s, strlen(s)));
 #endif
 }
@ -3848,7 +3843,8 @@ static int LuaFetch(lua_State *L) {
  usessl = false;
  if (url.scheme.n) {
 #ifndef UNSECURE
-    if (url.scheme.n == 5 && !memcasecmp(url.scheme.p, "https", 5)) {
+    if (!unsecure && url.scheme.n == 5 &&
+        !memcasecmp(url.scheme.p, "https", 5)) {
      usessl = true;
    } else
 #endif
@ -3858,14 +3854,20 @@ static int LuaFetch(lua_State *L) {
    }
  }

+#ifndef UNSECURE
  if (usessl && !sslinitialized) TlsInit();
+#endif

  if (url.host.n) {
    host = gc(strndup(url.host.p, url.host.n));
    if (url.port.n) {
      port = gc(strndup(url.port.p, url.port.n));
+#ifndef UNSECURE
+    } else if (usessl) {
+      port = "443";
+#endif
    } else {
-      port = usessl ? "443" : "80";
+      port = "80";
    }
  } else {
    ip = servers.n ? ntohl(servers.p[0].addr.sin_addr.s_addr) : INADDR_LOOPBACK;
@ -3932,6 +3934,7 @@ static int LuaFetch(lua_State *L) {
    unreachable;
  }

+#ifndef UNSECURE
  if (usessl) {
    if (sslcliused) {
      mbedtls_ssl_session_reset(&sslcli);
@ -3966,11 +3969,13 @@ static int LuaFetch(lua_State *L) {
             mbedtls_ssl_get_ciphersuite(&sslcli),
             mbedtls_ssl_get_version(&sslcli));
  }
+#endif /* UNSECURE */

  /*
   * Send HTTP Message.
   */
  DEBUGF("(ftch) client sending %s request", method);
+#ifndef UNSECURE
  if (usessl) {
    ret = mbedtls_ssl_write(&sslcli, request, requestlen);
    if (ret != requestlen) {
@ -3979,7 +3984,9 @@ static int LuaFetch(lua_State *L) {
      LuaThrowTlsError(L, "write", ret);
      unreachable;
    }
-  } else if (WRITE(sock, request, requestlen) != requestlen) {
+  } else
+#endif
+      if (WRITE(sock, request, requestlen) != requestlen) {
    close(sock);
    luaL_error(L, "write error: %s", strerror(errno));
    unreachable;
@ -4000,6 +4007,7 @@ static int LuaFetch(lua_State *L) {
      inbuf.p = realloc(inbuf.p, inbuf.c);
    }
    NOISEF("(ftch) client reading");
+#ifndef UNSECURE
    if (usessl) {
      if ((rc = mbedtls_ssl_read(&sslcli, inbuf.p + inbuf.n,
                                 inbuf.c - inbuf.n)) < 0) {
@ -4013,7 +4021,9 @@ static int LuaFetch(lua_State *L) {
          unreachable;
        }
      }
-    } else if ((rc = READ(sock, inbuf.p + inbuf.n, inbuf.c - inbuf.n)) == -1) {
+    } else
+#endif
+        if ((rc = READ(sock, inbuf.p + inbuf.n, inbuf.c - inbuf.n)) == -1) {
      close(sock);
      free(inbuf.p);
      DestroyHttpMessage(&msg);
@ -4163,6 +4173,7 @@ TransportError:
  close(sock);
  luaL_error(L, "transport error");
  unreachable;
+#ifndef UNSECURE
 VerifyFailed:
  LockInc(&shared->c.sslverifyfailed);
  close(sock);
@ -4170,6 +4181,7 @@ VerifyFailed:
      L, gc(DescribeSslVerifyFailure(sslcli.session_negotiate->verify_result)),
      ret);
  unreachable;
+#endif
 #undef ssl
 }

@ -4828,8 +4840,11 @@ static int LuaEvadeDragnetSurveillance(lua_State *L) {

 static int LuaProgramSslCompression(lua_State *L) {
 #ifndef UNSECURE
-  OnlyCallFromInitLua(L, "ProgramSslCompression");
-  conf.disable_compression = confcli.disable_compression = !lua_toboolean(L, 1);
+  if (!unsecure) {
+    OnlyCallFromInitLua(L, "ProgramSslCompression");
+    conf.disable_compression = confcli.disable_compression =
+        !lua_toboolean(L, 1);
+  }
 #endif
  return 0;
 }
@ -5071,6 +5086,7 @@ static const luaL_Reg kLuaFuncs[] = {
    {"EscapePath", LuaEscapePath},                        //
    {"EscapeSegment", LuaEscapeSegment},                  //
    {"EscapeUser", LuaEscapeUser},                        //
+    {"Fetch", LuaFetch},                                  //
    {"FormatHttpDateTime", LuaFormatHttpDateTime},        //
    {"FormatIp", LuaFormatIp},                            //
    {"GetAssetComment", LuaGetAssetComment},              //
@ -5194,7 +5210,6 @@ static const luaL_Reg kLuaFuncs[] = {
    {"hex", LuaHex},                                      //
    {"oct", LuaOct},                                      //
 #ifndef UNSECURE
-    {"Fetch", LuaFetch},                                        //
    {"EvadeDragnetSurveillance", LuaEvadeDragnetSurveillance},  //
    {"GetSslIdentity", LuaGetSslIdentity},                      //
    {"ProgramSslCiphersuite", LuaProgramSslCiphersuite},        //
@ -5541,6 +5556,7 @@ static char *HandleMapFailed(struct Asset *a, int fd) {
 }

 static void LogAcceptError(const char *s) {
+  LockInc(&shared->c.accepterrors);
  WARNF("(srvr) %s accept error: %s", DescribeServer(), s);
 }

@ -6270,14 +6286,16 @@ static void HandleMessages(void) {
 #ifndef UNSECURE
          if (!once) {
            once = true;
-            if (IsSsl(inbuf.p[0])) {
-              if (TlsSetup()) {
-                continue;
+            if (!unsecure) {
+              if (IsSsl(inbuf.p[0])) {
+                if (TlsSetup()) {
+                  continue;
+                } else {
+                  return;
+                }
              } else {
-                return;
+                WipeServingKeys();
              }
-            } else {
-              WipeServingKeys();
            }
          }
 #endif
@ -6300,15 +6318,15 @@ static void HandleMessages(void) {
        LockInc(&shared->c.readtimeouts);
        if (amtread) SendTimeout();
        NotifyClose();
-        LogClose("timeout");
+        LogClose("readtimeout");
        return;
      } else if (errno == ECONNRESET) {
        LockInc(&shared->c.readresets);
-        LogClose("reset");
+        LogClose("readreset");
        return;
      } else {
        LockInc(&shared->c.readerrors);
-        WARNF("(clnt) %s read error: %m", DescribeClient());
+        WARNF("(clnt) %s readerror: %m", DescribeClient());
        return;
      }
      if (killed || (terminated && !amtread) ||
@ -6339,7 +6357,7 @@ static void HandleMessages(void) {
    } else {
      CHECK_LT(msgsize, amtread);
      LockInc(&shared->c.pipelinedrequests);
-      DEBUGF("(stat) %,ld pipelined bytes", amtread - msgsize);
+      DEBUGF("(stat) %,ld pipelinedrequest bytes", amtread - msgsize);
      memmove(inbuf.p, inbuf.p + msgsize, amtread - msgsize);
      amtread -= msgsize;
      if (killed) {
@ -6488,7 +6506,7 @@ static int MemoryMonitor(void *arg) {
  long i, j, k, n, x, y, pi, gen, pages;
  int rc, id, color, color2, workers;
  _spinlock(&memmonalive);
-  __atomic_load(&shared->workers, &id, __ATOMIC_SEQ_CST);
+  id = atomic_load_explicit(&shared->workers, memory_order_relaxed);
  DEBUGF("(memv) started for pid %d on tid %d", getpid(), gettid());

  sigemptyset(&ss);
@ -6521,9 +6539,8 @@ static int MemoryMonitor(void *arg) {

  if (tty != -1) {
    for (gen = 0, mi = 0, b = 0;;) {
-      __atomic_load(&terminatemonitor, &done, __ATOMIC_SEQ_CST);
-      if (done) break;
-      __atomic_load(&shared->workers, &workers, __ATOMIC_SEQ_CST);
+      if (terminatemonitor) break;
+      workers = atomic_load_explicit(&shared->workers, memory_order_relaxed);
      if (id) id = MAX(1, MIN(id, workers));
      if (!id && workers) {
        usleep(50000);
@ -6531,7 +6548,7 @@ static int MemoryMonitor(void *arg) {
      }

      ++gen;
-      __atomic_load(&_mmi.i, &intervals, __ATOMIC_SEQ_CST);
+      intervals = atomic_load_explicit(&_mmi.i, memory_order_relaxed);
      if ((mi2 = realloc(mi, (intervals += 3) * sizeof(*mi)))) {
        mi = mi2;
        mi[0].x = (intptr_t)_base >> 16;
@ -6713,35 +6730,37 @@ static int HandleConnection(size_t i) {
      LockInc(&shared->c.acceptinterrupts);
    } else if (errno == ENFILE) {
      LockInc(&shared->c.enfiles);
-      LogAcceptError("too many open files");
+      LogAcceptError("enfile: too many open files");
      meltdown = true;
    } else if (errno == EMFILE) {
      LockInc(&shared->c.emfiles);
-      LogAcceptError("ran out of open file quota");
+      LogAcceptError("emfile: ran out of open file quota");
      meltdown = true;
    } else if (errno == ENOMEM) {
      LockInc(&shared->c.enomems);
-      LogAcceptError("ran out of memory");
+      LogAcceptError("enomem: ran out of memory");
      meltdown = true;
    } else if (errno == ENOBUFS) {
      LockInc(&shared->c.enobufs);
-      LogAcceptError("ran out of buffer");
+      LogAcceptError("enobuf: ran out of buffer");
      meltdown = true;
    } else if (errno == ENONET) {
      LockInc(&shared->c.enonets);
-      LogAcceptError("network gone");
+      LogAcceptError("enonet: network gone");
      polls[i].fd = -polls[i].fd;
    } else if (errno == ENETDOWN) {
      LockInc(&shared->c.enetdowns);
-      LogAcceptError("network down");
+      LogAcceptError("enetdown: network down");
      polls[i].fd = -polls[i].fd;
    } else if (errno == ECONNABORTED) {
+      LockInc(&shared->c.accepterrors);
      LockInc(&shared->c.acceptresets);
      WARNF("(srvr) %S accept error: %s", DescribeServer(),
-            "connection reset before accept");
+            "acceptreset: connection reset before accept");
    } else if (errno == ENETUNREACH || errno == EHOSTUNREACH ||
               errno == EOPNOTSUPP || errno == ENOPROTOOPT || errno == EPROTO) {
      LockInc(&shared->c.accepterrors);
+      LockInc(&shared->c.acceptflakes);
      WARNF("(srvr) accept error: %s ephemeral accept error: %m",
            DescribeServer());
    } else {
@ -6753,6 +6772,7 @@ static int HandleConnection(size_t i) {
 }

 static void RestoreApe(void) {
+  int ft;
  char *p;
  size_t n;
  struct Asset *a;
@ -6764,9 +6784,15 @@ static void RestoreApe(void) {
  if (endswith(zpath, ".com.dbg")) return;
  if ((a = GetAssetZip("/.ape", 5)) && (p = LoadAsset(a, &n))) {
    close(zfd);
+    ft = __ftrace;
    if ((zfd = OpenExecutable()) == -1 || WRITE(zfd, p, n) == -1) {
      WARNF("(srvr) can't restore .ape");
    }
+    if (ft > 0) {
+      __ftrace = 0;
+      ftrace_install();
+      __ftrace = ft;
+    }
    free(p);
  } else {
    DEBUGF("(srvr) /.ape not found");
@ -7036,6 +7062,7 @@ static void SigInit(void) {
 static void TlsInit(void) {
 #ifndef UNSECURE
  int suite;
+  if (unsecure) return;

  if (!sslinitialized) {
    InitializeRng(&rng);
@ -7095,6 +7122,7 @@ static void TlsInit(void) {

 static void TlsDestroy(void) {
 #ifndef UNSECURE
+  if (unsecure) return;
  mbedtls_ssl_free(&ssl);
  mbedtls_ssl_free(&sslcli);
  mbedtls_ctr_drbg_free(&rng);
@ -7139,6 +7167,7 @@ static void GetOpts(int argc, char *argv[]) {
      CASE('S', ++sandboxed);
      CASE('v', ++__log_level);
      CASE('s', --__log_level);
+      CASE('X', unsecure = true);
      CASE('Z', systrace = true);
      CASE('b', logbodies = true);
      CASE('z', printport = true);
--- a/tool/plinko/lib/plinko.c
+++ b/tool/plinko/lib/plinko.c
@ -674,9 +674,9 @@ struct T DispatchTrace(dword ea, dword tm, dword r, dword p1, dword p2,
 struct T DispatchFtrace(dword ea, dword tm, dword r, dword p1, dword p2,
                        dword d) {
  ftrace_install();
-  ++g_ftrace;
+  ++__ftrace;
  ea = MAKE(recurse(MAKE(Cadr(LO(ea)), HI(ea)), p1, p2), 0);
-  --g_ftrace;
+  --__ftrace;
  return Ret(ea, tm, r);
 }

--- a/tool/plinko/lib/printf.c
+++ b/tool/plinko/lib/printf.c
@ -80,7 +80,7 @@ int Vfnprintf(const char *f, va_list va, int fd, int n) {
  int b, c, i, x, y, si, prec, cols, sign;
  gotr = false;
  t = rdtsc();
-  --g_ftrace;
+  --__ftrace;
  --__strace;
  ++recursive;
  for (ansi = 0;;) {
@ -290,7 +290,7 @@ int Vfnprintf(const char *f, va_list va, int fd, int n) {
    }
  }
  --recursive;
-  ++g_ftrace;
+  ++__ftrace;
  ++__strace;
  if (!recursive) {
    u = rdtsc();
--- a/tool/plinko/lib/read.c
+++ b/tool/plinko/lib/read.c
@ -280,10 +280,10 @@ static int Read1(int fd) {

 int Read(int fd) {
  int r;
-  --g_ftrace;
+  --__ftrace;
  --__strace;
  r = Read1(fd);
-  ++g_ftrace;
+  ++__ftrace;
  ++__strace;
  return r;
 }
--- a/tool/plinko/plinko.c
+++ b/tool/plinko/plinko.c
@ -18,6 +18,7 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/intrin/kprintf.h"
 #include "libc/log/log.h"
+#include "libc/stdio/stdio.h"
 #include "tool/plinko/lib/plinko.h"

 STATIC_YOINK("__zipos_get");
--- a/tool/viz/echoctl.c
+++ b/tool/viz/echoctl.c
@ -0,0 +1,28 @@
+/*-*- 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.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/struct/termios.h"
+#include "libc/calls/termios.h"
+#include "libc/sysv/consts/termios.h"
+
+int main(int argc, char *argv[]) {
+  struct termios t;
+  if (tcgetattr(0, &t) == -1) return 1;
+  t.c_lflag ^= ECHOCTL;
+  if (tcsetattr(0, TCSANOW, &t) == -1) return 2;
+}
--- a/tool/viz/vdsodump.c
+++ b/tool/viz/vdsodump.c
@ -0,0 +1,81 @@
+/*-*- 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.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/struct/sigaction.h"
+#include "libc/calls/struct/siginfo.h"
+#include "libc/calls/ucontext.h"
+#include "libc/runtime/runtime.h"
+#include "libc/stdio/stdio.h"
+#include "libc/sysv/consts/auxv.h"
+#include "libc/sysv/consts/sa.h"
+#include "libc/sysv/consts/sig.h"
+#include "third_party/xed/x86.h"
+
+#define OUTPATH "vdso.elf"
+
+volatile bool finished;
+
+void OnSegmentationFault(int sig, siginfo_t *si, ucontext_t *ctx) {
+  struct XedDecodedInst xedd;
+  xed_decoded_inst_zero_set_mode(&xedd, XED_MACHINE_MODE_LONG_64);
+  xed_instruction_length_decode(&xedd, (void *)ctx->uc_mcontext.rip, 15);
+  ctx->uc_mcontext.rip += xedd.length;
+  finished = true;
+}
+
+int main(int argc, char *argv[]) {
+  FILE *f;
+  int byte;
+  volatile unsigned char *vdso, *p;
+
+  vdso = (unsigned char *)getauxval(AT_SYSINFO_EHDR);
+  if (vdso) {
+    fprintf(stderr, "vdso found at address %p\n", vdso);
+  } else {
+    fprintf(stderr, "error: AT_SYSINFO_EHDR was not in auxiliary values\n");
+    return 1;
+  }
+
+  f = fopen(OUTPATH, "wb");
+  if (!f) {
+    fprintf(stderr, "error: fopen(%`'s) failed\n", OUTPATH);
+    return 1;
+  }
+
+  struct sigaction sa = {
+      .sa_sigaction = OnSegmentationFault,
+      .sa_flags = SA_SIGINFO,
+  };
+  sigaction(SIGSEGV, &sa, 0);
+  sigaction(SIGBUS, &sa, 0);
+
+  p = vdso;
+  for (;;) {
+    byte = *p++;
+    if (!finished) {
+      fputc(byte, f);
+    } else {
+      break;
+    }
+  }
+
+  fclose(f);
+  fprintf(stderr, "%zu bytes dumped to %s\n", p - vdso, OUTPATH);
+
+  return 0;
+}