feat: introduce onUsr2 and onUsr1

user/nesttarget.c

@@ -0,0 +1,153 @@
+#include "ulib.h"
+
+/*
+ * Only ever spawned by nesttest.c, with three shared pipe handles as argv
+ * (ready/handlerReady/go, decToString'd -- the same convention jobtest.c's
+ * two-pipe rendezvous already established, extended to three because this
+ * needs an extra one to announce "the handler has genuinely entered and is
+ * about to block" from INSIDE a signal handler, not main()).
+ *
+ * Proves real, ring-3 NESTED signal delivery end to end (signal.h's
+ * per-signal sa_mask / Thread.sigHandlerDepth): onUsr1 installs no sa_mask
+ * at all (mask 0), so sigUsr2 arriving while it is still active is not
+ * blocked by anything -- it genuinely interrupts onUsr1 with its own,
+ * separate trampoline entry, onUsr1 resuming afterwards exactly where the
+ * blocking read below left it. No sleep/timing guess: the three pipes make
+ * "handler installed", "handler entered and blocked", and "safe to unblock
+ * it" all real happens-before rendezvous, the same discipline sigtarget.c/
+ * jobtest.c already established for different races.
+ */
+
+static volatile int handlerUsr1Entered = 0;
+static volatile int handlerUsr2FiredNested = 0;
+static volatile int handlerUsr1Resumed = 0;
+
+static long handlerReadyFd = -1;
+static long goFd = -1;
+
+static void onUsr2(int signum)
+{
+    (void)signum;
+    print("nesttarget: usr2-handler-fired-nested\n");
+    handlerUsr2FiredNested = 1;
+}
+
+static void onUsr1(int signum)
+{
+    (void)signum;
+    print("nesttarget: usr1-handler-enter\n");
+    handlerUsr1Entered = 1;
+
+    /* Announces "I am about to block on goFd" from INSIDE the handler --
+       nesttest.c will not send sigUsr2 until it reads this byte, so sigUsr2
+       can never race ahead of onUsr1 actually being active. */
+    if (userWrite((int)handlerReadyFd, "h", 1) != 1) {
+        print("nesttarget: FAIL write handler-ready byte\n");
+        return;
+    }
+    userClose((int)handlerReadyFd);
+
+    char goByte = 0;
+    /* Real blocking read, issued BY THE HANDLER ITSELF: the moment it
+       completes, control returns to ring 3 through the exact same
+       int 0x80 path any syscall does, which isr.c's deliverPendingSignals
+       always re-checks -- if sigUsr2 is pending and unblocked by then (it
+       is: onUsr1's own sa_mask is empty), it is delivered as a genuinely
+       NESTED handler right here, before this function's next line ever
+       runs. */
+    if (userRead((int)goFd, &goByte, 1) != 1) {
+        print("nesttarget: FAIL read go byte inside handler\n");
+        return;
+    }
+    userClose((int)goFd);
+
+    print("nesttarget: usr1-handler-resumed-after-nested-usr2\n");
+    handlerUsr1Resumed = 1;
+}
+
+int main(int argc, char** argv)
+{
+    print("nesttarget: start, pid=");
+    printDec(userGetpid());
+    print("\n");
+
+    if (argc != 4) {
+        print("nesttarget: FAIL expected three argv (ready/handlerReady/go handles)\n");
+        return 1;
+    }
+
+    long readyHandle = parseDec(argv[1]);
+    long handlerReadyHandle = parseDec(argv[2]);
+    long goHandle = parseDec(argv[3]);
+
+    /* sigUsr1's sa_mask is 0 (no additional blocking) so sigUsr2 -- also
+       unmasked -- can genuinely nest inside it; sigUsr2 has no mask of its
+       own either, since nothing is meant to interrupt IT here. sigUsr1's
+       own delivery always interrupts main()'s plain userSleep loop below
+       (never a retryable syscall), so its sa_flags is irrelevant either
+       way. sigUsr2, though, genuinely interrupts onUsr1's OWN blocking
+       userRead(goFd) -- this test's whole point is that read transparently
+       resumes and returns the real byte once onUsr2 returns, so sigUsr2
+       is registered WITH sigFlagRestart (signalnum.h); without it, that
+       read would return errInterrupted instead, which
+       user/restarttarget.c -- not this file -- is what actually exercises. */
+    if (userSigAction(sigUsr1, onUsr1, 0, 0) == (long)sigSetFailed ||
+        userSigAction(sigUsr2, onUsr2, 0, sigFlagRestart) == (long)sigSetFailed) {
+        print("nesttarget: FAIL install handlers\n");
+        return 1;
+    }
+
+    /* Attach the pipes THIS process will use from inside a handler before
+       ever installing/receiving anything that could reach them -- same
+       "attach first" discipline sigtest.c/jobtest.c document at length, so
+       neither slot can be reclaimed out from under a late attach. */
+    handlerReadyFd = userPipeAttach(handlerReadyHandle, 1);
+    goFd = userPipeAttach(goHandle, 0);
+    if (handlerReadyFd < 0 || goFd < 0) {
+        print("nesttarget: FAIL attach handler-ready/go pipes\n");
+        return 1;
+    }
+
+    long readyFd = userPipeAttach(readyHandle, 1);
+    if (readyFd < 0) {
+        print("nesttarget: FAIL attach ready pipe\n");
+        return 1;
+    }
+    if (userWrite((int)readyFd, "r", 1) != 1) {
+        print("nesttarget: FAIL write ready byte\n");
+        return 1;
+    }
+    userClose((int)readyFd);
+    print("nesttarget: ready, waiting for sigUsr1\n");
+
+    /* Several short sleeps rather than one long one -- this kernel only
+       checks for a pending signal when the target thread actually returns
+       to ring 3 (isr.c's deliverPendingSignals), the same reasoning
+       sigtarget.c's own poll loop documents. Once onUsr1 fires, ALL the
+       real work (including the nested onUsr2) happens synchronously inside
+       it before it ever returns here. */
+    for (int i = 0; i < 80 && !handlerUsr1Resumed; i++)
+        userSleep(20);
+
+    if (!handlerUsr1Entered) {
+        print("nesttarget: FAIL usr1 handler never fired\n");
+        return 1;
+    }
+    if (!handlerUsr2FiredNested) {
+        print("nesttarget: FAIL usr2 handler never fired nested inside usr1\n");
+        return 1;
+    }
+    if (!handlerUsr1Resumed) {
+        print("nesttarget: FAIL usr1 handler never resumed after nested usr2\n");
+        return 1;
+    }
+    print("nesttarget: nested-delivery-ok\n");
+
+    /* Reached only if BOTH sysSigReturn calls (the nested usr2's and then
+       usr1's own) correctly restored their respective saved contexts --
+       a corrupted pop at either depth would have crashed, hung, or
+       resumed the wrong one of the two saved trapframes instead of
+       returning here from onUsr1's own return. */
+    print("nesttarget: resumed-after-both-handlers-ok\n");
+    return 77;
+}