Implement raise() with getcontext() / setcontext()

Author: jart

libc/calls/getcontext.S

@@ -20,12 +20,6 @@
 
 //	Gets machine state.
 //
-//	This function goes 14x slower if sigaction() has ever been used to
-//	install a signal handling function. If you don't care about signal
-//	safety and just want fast fibers, then you may override the global
-//	variable `__interruptible` to disable the sigprocmask() calls, for
-//	pure userspace context switching.
-//
 //	@return	0 on success, or -1 w/ errno
 //	@see	makecontext()
 //	@see	swapcontext()

libc/calls/raise.c

@@ -23,6 +23,7 @@
 #include "libc/intrin/strace.internal.h"
 #include "libc/runtime/syslib.internal.h"
 #include "libc/sysv/consts/sicode.h"
+#include "libc/sysv/errfuns.h"
 
 /**
  * Sends signal to self.
@@ -35,15 +36,20 @@
  *
  * @param sig can be SIGALRM, SIGINT, SIGTERM, SIGKILL, etc.
  * @return 0 on success, or nonzero on failure
+ * @raise EINVAL if `sig` is invalid
  * @asyncsignalsafe
  */
 int raise(int sig) {
   int rc;
   if (IsXnuSilicon()) {
     rc = __syslib->__raise(sig);
   } else if (IsWindows()) {
-    __sig_raise(sig, SI_TKILL);
-    rc = 0;
+    if (0 <= sig && sig <= 64) {
+      __sig_raise(sig, SI_TKILL);
+      rc = 0;
+    } else {
+      rc = einval();
+    }
   } else {
     rc = sys_tkill(gettid(), sig, 0);
   }

libc/calls/sig.c

@@ -34,6 +34,7 @@
 #include "libc/intrin/atomic.h"
 #include "libc/intrin/bsf.h"
 #include "libc/intrin/describebacktrace.internal.h"
+#include "libc/intrin/kprintf.h"
 #include "libc/intrin/popcnt.h"
 #include "libc/intrin/strace.internal.h"
 #include "libc/intrin/weaken.h"
@@ -169,53 +170,59 @@ static textwindows bool __sig_start(struct PosixThread *pt, int sig,
 }
 
 static textwindows sigaction_f __sig_handler(unsigned rva) {
+  atomic_fetch_add_explicit(&__sig.count, 1, memory_order_relaxed);
   return (sigaction_f)(__executable_start + rva);
 }
 
-textwindows int __sig_raise(int sig, int sic) {
+textwindows int __sig_raise(volatile int sig, int sic) {
 
-  // create machine context object
-  struct PosixThread *pt = _pthread_self();
-  ucontext_t ctx = {.uc_sigmask = pt->tib->tib_sigmask};
-  struct NtContext nc;
-  nc.ContextFlags = kNtContextFull;
-  GetThreadContext(GetCurrentThread(), &nc);
-  _ntcontext2linux(&ctx, &nc);
+  // bitset of kinds of handlers called
+  volatile int handler_was_called = 0;
 
-  // process signal(s)
-  int handler_was_called = 0;
-  do {
-    // start the signal
-    unsigned rva, flags;
-    if (__sig_start(pt, sig, &rva, &flags)) {
-      if (flags & SA_RESETHAND) {
-        STRACE("resetting %G handler", sig);
-        __sighandrvas[sig] = (int32_t)(intptr_t)SIG_DFL;
-      }
+  // loop over pending signals
+  ucontext_t ctx;
+  getcontext(&ctx);
+  if (!sig) {
+    if ((sig = __sig_get(ctx.uc_sigmask))) {
+      sic = SI_KERNEL;
+    } else {
+      return handler_was_called;
+    }
+  }
 
-      // update the signal mask in preparation for signal handller
-      sigset_t blocksigs = __sighandmask[sig];
-      if (!(flags & SA_NODEFER)) blocksigs |= 1ull << (sig - 1);
-      ctx.uc_sigmask = atomic_fetch_or_explicit(
-          &pt->tib->tib_sigmask, blocksigs, memory_order_acquire);
-
-      // call the user's signal handler
-      char ssbuf[2][128];
-      siginfo_t si = {.si_signo = sig, .si_code = sic};
-      STRACE("__sig_raise(%G, %t) mask %s → %s", sig, __sig_handler(rva),
-             (DescribeSigset)(ssbuf[0], 0, &ctx.uc_sigmask),
-             (DescribeSigset)(ssbuf[1], 0, (sigset_t *)&pt->tib->tib_sigmask));
-      __sig_handler(rva)(sig, &si, &ctx);
-      (void)ssbuf;
-
-      // restore the original signal mask
-      atomic_store_explicit(&pt->tib->tib_sigmask, ctx.uc_sigmask,
-                            memory_order_release);
-      handler_was_called |= (flags & SA_RESTART) ? 2 : 1;
+  // process signal(s)
+  unsigned rva, flags;
+  struct PosixThread *pt = _pthread_self();
+  if (__sig_start(pt, sig, &rva, &flags)) {
+    if (flags & SA_RESETHAND) {
+      STRACE("resetting %G handler", sig);
+      __sighandrvas[sig] = (int32_t)(intptr_t)SIG_DFL;
     }
-    sic = SI_KERNEL;
-  } while ((sig = __sig_get(ctx.uc_sigmask)));
-  return handler_was_called;
+
+    // update the signal mask in preparation for signal handller
+    sigset_t blocksigs = __sighandmask[sig];
+    if (!(flags & SA_NODEFER)) blocksigs |= 1ull << (sig - 1);
+    ctx.uc_sigmask = atomic_fetch_or_explicit(&pt->tib->tib_sigmask, blocksigs,
+                                              memory_order_acquire);
+
+    // call the user's signal handler
+    char ssbuf[2][128];
+    siginfo_t si = {.si_signo = sig, .si_code = sic};
+    STRACE("__sig_raise(%G, %t) mask %s → %s", sig, __sig_handler(rva),
+           (DescribeSigset)(ssbuf[0], 0, &ctx.uc_sigmask),
+           (DescribeSigset)(ssbuf[1], 0, (sigset_t *)&pt->tib->tib_sigmask));
+    __sig_handler(rva)(sig, &si, &ctx);
+    (void)ssbuf;
+
+    // record this handler
+    handler_was_called |= (flags & SA_RESTART) ? 2 : 1;
+  }
+
+  // restore sigmask
+  // loop back to top
+  // jump where handler says
+  sig = 0;
+  return setcontext(&ctx);
 }
 
 textwindows int __sig_relay(int sig, int sic, sigset_t waitmask) {
@@ -258,7 +265,6 @@ static textwindows wontreturn void __sig_tramp(struct SignalFrame *sf) {
   struct CosmoTib *tib = __get_tls();
   struct PosixThread *pt = (struct PosixThread *)tib->tib_pthread;
   for (;;) {
-    atomic_fetch_add_explicit(&__sig.count, 1, memory_order_relaxed);
 
     // update the signal mask in preparation for signal handller
     sigset_t blocksigs = __sighandmask[sig];
@@ -513,9 +519,6 @@ static int __sig_crash_sig(struct NtExceptionPointers *ep, int *code) {
 static void __sig_unmaskable(struct NtExceptionPointers *ep, int code, int sig,
                              struct CosmoTib *tib) {
 
-  // increment the signal count for getrusage()
-  atomic_fetch_add_explicit(&__sig.count, 1, memory_order_relaxed);
-
   // log vital crash information reliably for --strace before doing much
   // we don't print this without the flag since raw numbers scare people
   // this needs at least one page of stack memory in order to get logged

libc/calls/sigaction.c

@@ -479,13 +479,6 @@ static int __sigaction(int sig, const struct sigaction *act,
  *   spawned your process, happened to call `setrlimit()`. Doing this is
  *   a wonderful idea.
  *
- * Using signals might make your C runtime slower. Upon successfully
- * installing its first signal handling function, sigaction() will set
- * the global variable `__interruptible` to true, to let everything else
- * know that signals are in play. That way code which would otherwise be
- * frequently calling sigprocmask() out of an abundance of caution, will
- * no longer need to pay its outrageous cost.
- *
  * Signal handlers should avoid clobbering global variables like `errno`
  * because most signals are asynchronous, i.e. the signal handler might
  * be called at any assembly instruction. If something like a `SIGCHLD`
@@ -506,13 +499,6 @@ int sigaction(int sig, const struct sigaction *act, struct sigaction *oldact) {
     rc = einval();
   } else {
     rc = __sigaction(sig, act, oldact);
-    if (!rc && act && (uintptr_t)act->sa_handler >= kSigactionMinRva) {
-      static bool once;
-      if (!once) {
-        __interruptible = true;
-        once = true;
-      }
-    }
   }
   STRACE("sigaction(%G, %s, [%s]) → %d% m", sig, DescribeSigaction(0, act),
          DescribeSigaction(rc, oldact), rc);

libc/calls/swapcontext.S

@@ -27,12 +27,6 @@
 //
 //	    swapcontext(x, y);
 //
-//	This function goes 14x slower if sigaction() has ever been used to
-//	install a signal handling function. If you don't care about signal
-//	safety and just want fast fibers, then you may override the global
-//	variable `__interruptible` to disable the sigprocmask() calls, for
-//	pure userspace context switching.
-//
 //	@return	0 on success, or -1 w/ errno
 //	@returnstwice
 	.ftrace1

libc/calls/ucontext.c

@@ -24,21 +24,13 @@
 int __tailcontext(const ucontext_t *);
 
 static int __contextmask(const sigset_t *opt_set, sigset_t *opt_out_oldset) {
-  if (!__interruptible) return 0;
-  // signal handling functions might exist
   // now context switching needs to go 14x slower
   return sigprocmask(SIG_SETMASK, opt_set, opt_out_oldset);
 }
 
 /**
  * Sets machine context.
  *
- * This function goes 14x slower if sigaction() has ever been used to
- * install a signal handling function. If you don't care about signal
- * safety and just want fast fibers, then you may override the global
- * variable `__interruptible` to disable the sigprocmask() calls, for
- * pure userspace context switching.
- *
  * @return -1 on error w/ errno, otherwise won't return unless sent back
  * @see swapcontext()
  * @see makecontext()

libc/nexgen32e/threaded.c

@@ -23,11 +23,6 @@
  */
 int __threaded;
 
-/**
- * Set to true if sigaction() has installed signal handlers.
- */
-bool __interruptible;
-
 #ifdef __x86_64__
 bool __tls_enabled;
 #endif

libc/runtime/runtime.h

@@ -72,7 +72,6 @@ extern int __argc;
 extern char **__argv;
 extern char **__envp;
 extern unsigned long *__auxv;
-extern bool __interruptible;
 extern intptr_t __oldstack;
 extern uint64_t __nosync;
 extern int __strace;

test/libc/calls/getcontext_test.c

@@ -54,7 +54,6 @@ TEST(getcontext, test) {
 TEST(getcontext, canReadAndWriteSignalMask) {
   sigset_t ss, old;
   volatile int n = 0;
-  __interruptible = true;
   sigemptyset(&ss);
   sigaddset(&ss, SIGUSR1);
   sigprocmask(SIG_SETMASK, &ss, &old);
@@ -72,8 +71,7 @@ TEST(getcontext, canReadAndWriteSignalMask) {
 }
 
 void SetGetContext(void) {
-  static int a;
-  a = 0;
+  int a = 0;
   getcontext(&context);
   if (!a) {
     a = 1;
@@ -82,9 +80,6 @@ void SetGetContext(void) {
 }
 
 BENCH(getcontext, bench) {
-  __interruptible = false;
-  EZBENCH2("getsetcontext nosig", donothing, SetGetContext());
-  __interruptible = true;
   EZBENCH2("getsetcontext", donothing, SetGetContext());
 }
 
@@ -99,10 +94,6 @@ BENCH(swapcontext, bench) {
     }
   } else {
     ready = true;
-    __interruptible = false;
-    EZBENCH2("swapcontextx2 nosig", donothing, swapcontext(&loop, &main));
-    // kprintf("dollar\n");
-    __interruptible = true;
     EZBENCH2("swapcontextx2", donothing, swapcontext(&loop, &main));
     // kprintf("dollar\n");
   }

test/libc/calls/raise_test.c

@@ -20,10 +20,12 @@
 #include "libc/calls/struct/sigaction.h"
 #include "libc/calls/struct/siginfo.h"
 #include "libc/dce.h"
+#include "libc/intrin/kprintf.h"
 #include "libc/runtime/runtime.h"
 #include "libc/sysv/consts/sa.h"
 #include "libc/sysv/consts/sicode.h"
 #include "libc/sysv/consts/sig.h"
+#include "libc/testlib/ezbench.h"
 #include "libc/testlib/subprocess.h"
 #include "libc/testlib/testlib.h"
 #include "libc/thread/thread.h"
@@ -67,9 +69,19 @@ void *Worker(void *arg) {
 }
 
 TEST(raise, threaded) {
+  SPAWN(fork);
   signal(SIGILL, SIG_DFL);
   pthread_t worker;
   ASSERT_EQ(0, pthread_create(&worker, 0, Worker, 0));
   ASSERT_EQ(0, pthread_join(worker, 0));
   pthread_exit(0);
+  EXITS(0);
+}
+
+void OnRaise(int sig) {
+}
+
+BENCH(raise, bench) {
+  signal(SIGUSR1, OnRaise);
+  EZBENCH2("raise", donothing, raise(SIGUSR1));
 }