Fix broken debugger/debuggee startup handshake protocol on macOS26. (#118120)

* Add support for new startup handshake protocol over pipes instead of sempahores.

* Remove NonBlocking runtime support.

* Renames, logging and simplification.

* Improve tracing.

* Make open check non blocking.

* Fold access into open calls and track ENOENT | ENOACCES

* Review feedback.

Author: lateralusX

src/coreclr/pal/src/thread/process.cpp

@@ -93,6 +93,9 @@ extern "C"
         }                                                                   \
     } while (false)
 
+// On macOS 26, sem_open fails if debugger and debugee are signed with different team ids.
+// Use fifos instead of semaphores to avoid this issue, https://github.com/dotnet/runtime/issues/116545
+#define ENABLE_RUNTIME_EVENTS_OVER_PIPES
 #endif // __APPLE__
 
 #ifdef __NetBSD__
@@ -1401,21 +1404,217 @@ static uint64_t HashSemaphoreName(uint64_t a, uint64_t b)
 static const char *const TwoWayNamedPipePrefix = "clr-debug-pipe";
 static const char* IpcNameFormat = "%s-%d-%llu-%s";
 
-/*++
-    PAL_NotifyRuntimeStarted
+#ifdef ENABLE_RUNTIME_EVENTS_OVER_PIPES
+static const char* RuntimeStartupPipeName = "st";
+static const char* RuntimeContinuePipeName = "co";
 
-    Signals the debugger waiting for runtime startup notification to continue and
-    waits until the debugger signals us to continue.
+#define PIPE_OPEN_RETRY_DELAY_NS 500000000 // 500 ms
 
-Parameters:
-    None
+typedef enum
+{
+    RuntimeEventsOverPipes_Disabled = 0,
+    RuntimeEventsOverPipes_Succeeded = 1,
+    RuntimeEventsOverPipes_Failed = 2,
+} RuntimeEventsOverPipes;
 
-Return value:
-    TRUE - successfully launched by debugger, FALSE - not launched or some failure in the handshake
---*/
+typedef enum
+{
+    RuntimeEvent_Unknown = 0,
+    RuntimeEvent_Started = 1,
+    RuntimeEvent_Continue = 2,
+} RuntimeEvent;
+
+static
+int
+OpenPipe(const char* name, int mode)
+{
+    int fd = -1;
+    int flags = mode | O_NONBLOCK;
+
+#if defined(FD_CLOEXEC)
+    flags |= O_CLOEXEC;
+#endif
+
+    while (fd == -1)
+    {
+        fd = open(name, flags);
+        if (fd == -1)
+        {
+            if (mode == O_WRONLY && errno == ENXIO)
+            {
+                PAL_nanosleep(PIPE_OPEN_RETRY_DELAY_NS);
+                continue;
+            }
+            else if (errno == EINTR)
+            {
+                continue;
+            }
+            else
+            {
+                break;
+            }
+        }
+    }
+
+    if (fd != -1)
+    {
+        flags = fcntl(fd, F_GETFL);
+        if (flags != -1)
+        {
+            flags &= ~O_NONBLOCK;
+            if (fcntl(fd, F_SETFL, flags) == -1)
+            {
+                close(fd);
+                fd = -1;
+            }
+        }
+        else
+        {
+            close(fd);
+            fd = -1;
+        }
+    }
+
+    return fd;
+}
+
+static
+void
+ClosePipe(int fd)
+{
+    if (fd != -1)
+    {
+        while (close(fd) < 0 && errno == EINTR);
+    }
+}
+
+static
+RuntimeEventsOverPipes
+NotifyRuntimeUsingPipes()
+{
+    RuntimeEventsOverPipes result = RuntimeEventsOverPipes_Disabled;
+    char startupPipeName[MAX_DEBUGGER_TRANSPORT_PIPE_NAME_LENGTH];
+    char continuePipeName[MAX_DEBUGGER_TRANSPORT_PIPE_NAME_LENGTH];
+    int startupPipeFd = -1;
+    int continuePipeFd = -1;
+    size_t offset = 0;
+
+    LPCSTR applicationGroupId = PAL_GetApplicationGroupId();
+
+    PAL_GetTransportPipeName(continuePipeName, gPID, applicationGroupId, RuntimeContinuePipeName);
+    TRACE("NotifyRuntimeUsingPipes: opening continue '%s' pipe\n", continuePipeName);
+
+    continuePipeFd = OpenPipe(continuePipeName, O_RDONLY);
+    if (continuePipeFd == -1)
+    {
+        if (errno == ENOENT || errno == EACCES)
+        {
+            TRACE("NotifyRuntimeUsingPipes: pipe %s not found/accessible, runtime events over pipes disabled\n", continuePipeName);
+        }
+        else
+        {
+            TRACE("NotifyRuntimeUsingPipes: open(%s) failed: %d (%s)\n", continuePipeName, errno, strerror(errno));
+            result = RuntimeEventsOverPipes_Failed;
+        }
+
+        goto exit;
+    }
+
+    PAL_GetTransportPipeName(startupPipeName, gPID, applicationGroupId, RuntimeStartupPipeName);
+    TRACE("NotifyRuntimeUsingPipes: opening startup '%s' pipe\n", startupPipeName);
+
+    startupPipeFd = OpenPipe(startupPipeName, O_WRONLY);
+    if (startupPipeFd == -1)
+    {
+        if (errno == ENOENT || errno == EACCES)
+        {
+            TRACE("NotifyRuntimeUsingPipes: pipe %s not found/accessible, runtime events over pipes disabled\n", startupPipeName);
+        }
+        else
+        {
+            TRACE("NotifyRuntimeUsingPipes: open(%s) failed: %d (%s)\n", startupPipeName, errno, strerror(errno));
+            result = RuntimeEventsOverPipes_Failed;
+        }
+
+        goto exit;
+    }
+
+    TRACE("NotifyRuntimeUsingPipes: sending started event\n");
+
+    {
+        unsigned char event = (unsigned char)RuntimeEvent_Started;
+        unsigned char *buffer = &event;
+        int bytesToWrite = sizeof(event);
+        int bytesWritten = 0;
+
+        do
+        {
+            bytesWritten = write(startupPipeFd, buffer + offset, bytesToWrite - offset);
+            if (bytesWritten > 0)
+            {
+                offset += bytesWritten;
+            }
+        }
+        while ((bytesWritten > 0 && offset < bytesToWrite) || (bytesWritten == -1 && errno == EINTR));
+
+        if (offset != bytesToWrite)
+        {
+            TRACE("NotifyRuntimeUsingPipes: write(%s) failed: %d (%s)\n", startupPipeName, errno, strerror(errno));
+            goto exit;
+        }
+    }
+
+    TRACE("NotifyRuntimeUsingPipes: waiting on continue event\n");
+
+    {
+        unsigned char event = (unsigned char)RuntimeEvent_Unknown;
+        unsigned char *buffer = &event;
+        int bytesToRead = sizeof(event);
+        int bytesRead = 0;
+
+        offset = 0;
+        do
+        {
+            bytesRead = read(continuePipeFd, buffer + offset, bytesToRead - offset);
+            if (bytesRead > 0)
+            {
+                offset += bytesRead;
+            }
+        }
+        while ((bytesRead > 0 && offset < bytesToRead) || (bytesRead == -1 && errno == EINTR));
+
+        if (offset == bytesToRead && event == (unsigned char)RuntimeEvent_Continue)
+        {
+            TRACE("NotifyRuntimeUsingPipes: received continue event\n");
+        }
+        else
+        {
+            TRACE("NotifyRuntimeUsingPipes: received invalid event\n");
+            goto exit;
+        }
+    }
+
+    result = RuntimeEventsOverPipes_Succeeded;
+
+exit:
+
+    if (startupPipeFd != -1)
+    {
+        ClosePipe(startupPipeFd);
+    }
+
+    if (continuePipeFd != -1)
+    {
+        ClosePipe(continuePipeFd);
+    }
+
+    return result;
+}
+#endif // ENABLE_RUNTIME_EVENTS_OVER_PIPES
+
+static
 BOOL
-PALAPI
-PAL_NotifyRuntimeStarted()
+NotifyRuntimeUsingSemaphores()
 {
     char startupSemName[CLR_SEM_MAX_NAMELEN];
     char continueSemName[CLR_SEM_MAX_NAMELEN];
@@ -1436,13 +1635,13 @@ PAL_NotifyRuntimeStarted()
     CreateSemaphoreName(startupSemName, RuntimeStartupSemaphoreName, unambiguousProcessDescriptor, applicationGroupId);
     CreateSemaphoreName(continueSemName, RuntimeContinueSemaphoreName, unambiguousProcessDescriptor, applicationGroupId);
 
-    TRACE("PAL_NotifyRuntimeStarted opening continue '%s' startup '%s'\n", continueSemName, startupSemName);
+    TRACE("NotifyRuntimeUsingSemaphores: opening continue '%s' startup '%s'\n", continueSemName, startupSemName);
 
     // Open the debugger startup semaphore. If it doesn't exists, then we do nothing and return
     startupSem = sem_open(startupSemName, 0);
     if (startupSem == SEM_FAILED)
     {
-        TRACE("sem_open(%s) failed: %d (%s)\n", startupSemName, errno, strerror(errno));
+        TRACE("NotifyRuntimeUsingSemaphores: sem_open(%s) failed: %d (%s)\n", startupSemName, errno, strerror(errno));
         goto exit;
     }
 
@@ -1465,7 +1664,7 @@ PAL_NotifyRuntimeStarted()
     {
         if (EINTR == errno)
         {
-            TRACE("sem_wait() failed with EINTR; re-waiting");
+            TRACE("NotifyRuntimeUsingSemaphores: sem_wait() failed with EINTR; re-waiting");
             continue;
         }
         ASSERT("sem_wait(continueSem) failed: errno is %d (%s)\n", errno, strerror(errno));
@@ -1487,6 +1686,45 @@ PAL_NotifyRuntimeStarted()
     return launched;
 }
 
+/*++
+    PAL_NotifyRuntimeStarted
+
+    Signals the debugger waiting for runtime startup notification to continue and
+    waits until the debugger signals us to continue.
+
+Parameters:
+    None
+
+Return value:
+    TRUE - successfully launched by debugger, FALSE - not launched or some failure in the handshake
+--*/
+BOOL
+PALAPI
+PAL_NotifyRuntimeStarted()
+{
+#ifdef ENABLE_RUNTIME_EVENTS_OVER_PIPES
+    // Test pipes as runtime event transport.
+    RuntimeEventsOverPipes result = NotifyRuntimeUsingPipes();
+    switch (result)
+    {
+    case RuntimeEventsOverPipes_Disabled:
+        TRACE("PAL_NotifyRuntimeStarted: pipe handshake disabled, try semaphores\n");
+        return NotifyRuntimeUsingSemaphores();
+    case RuntimeEventsOverPipes_Failed:
+        TRACE("PAL_NotifyRuntimeStarted: pipe handshake failed\n");
+        return FALSE;
+    case RuntimeEventsOverPipes_Succeeded:
+        TRACE("PAL_NotifyRuntimeStarted: pipe handshake succeeded\n");
+        return TRUE;
+    default:
+        // Unexpected result.
+        return FALSE;
+    }
+#else
+    return NotifyRuntimeUsingSemaphores();
+#endif // ENABLE_RUNTIME_EVENTS_OVER_PIPES
+}
+
 LPCSTR
 PALAPI
 PAL_GetApplicationGroupId()