libc: support syscall(SYS_thr_self,...)

This syscall returns the thread ID / light-weight PID of the calling
thread under FreeBSD.

Issue #2791

repos/libports/include/libc-genode/sys/syscall.h

@@ -1,4 +1,19 @@
 /*
- * This file is just here to prevent a compiler warning about the missing include file.
- * On Genode, we do not support calling syscalls directly via a libc mechanism.
+ * \brief  Minimal support for FreeBSD-specific syscalls
+ * \author Christian Helmuth
+ * \date   2018-05-16
  */
+
+/*
+ * Copyright (C) 2018 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+#ifndef _INCLUDE__LIBC_GENODE__SYS__SYSCALL_H_
+#define _INCLUDE__LIBC_GENODE__SYS__SYSCALL_H_
+
+#define SYS_thr_self 432  /* pid_t gettid() */
+
+#endif /* _INCLUDE__LIBC_GENODE__SYS__SYSCALL_H_ */

repos/libports/lib/mk/libc.mk

@@ -16,7 +16,7 @@ SRC_CC = atexit.cc dummies.cc rlimit.cc sysctl.cc \
          plugin.cc plugin_registry.cc select.cc exit.cc environ.cc nanosleep.cc \
          pread_pwrite.cc readv_writev.cc poll.cc \
          libc_pdbg.cc vfs_plugin.cc rtc.cc dynamic_linker.cc signal.cc \
-         socket_operations.cc task.cc socket_fs_plugin.cc
+         socket_operations.cc task.cc socket_fs_plugin.cc syscall.cc
 
 CC_OPT_sysctl += -Wno-write-strings
 

repos/libports/lib/symbols/libc

@@ -755,6 +755,7 @@ sys_nerr R 4
 sys_nsig R 4
 sys_siglist D 256
 sys_signame D 256
+syscall T
 sysconf T
 sysctl T
 sysctlbyname T

repos/libports/src/lib/libc/syscall.cc

@@ -0,0 +1,44 @@
+/*
+ * \brief  Minimal support for FreeBSD-specific syscalls
+ * \author Christian Helmuth
+ * \date   2018-05-16
+ */
+
+/*
+ * Copyright (C) 2018 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+/* Genode includes */
+#include <base/thread.h>
+
+/* libc includes */
+#include <errno.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+
+
+static int sys_thr_self()
+{
+	using Genode::addr_t;
+
+	addr_t const base  = Genode::Thread::stack_area_virtual_base();
+	addr_t const size  = Genode::Thread::stack_virtual_size();
+	addr_t const stack = (addr_t)Genode::Thread::myself()->stack_base();
+
+	return int((stack - base) / size + 1);
+}
+
+
+extern "C" int syscall(int nr, ...)
+{
+	switch (nr) {
+	case SYS_thr_self: return sys_thr_self();
+
+	default:
+		errno = ENOSYS;
+		return -1;
+	}
+}

repos/libports/src/test/libc/main.cc

@@ -24,6 +24,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <sys/syscall.h>
 
 
 int main(int argc, char **argv)
@@ -117,5 +120,22 @@ int main(int argc, char **argv)
 		}
 	}
 
+	{
+		pid_t const tid = syscall(SYS_thr_self);
+		if (tid == -1) {
+			printf("syscall(SYS_thr_self) returned %d (%s) - ERROR\n", tid, strerror(errno));
+			++error_count;
+		} else {
+			printf("syscall(SYS_thr_self) returned %d\n", tid);
+		}
+		int const ret = syscall(0xffff);
+		if (ret != -1) {
+			printf("syscall(unknown) returned %d - ERROR\n", ret);
+			++error_count;
+		} else {
+			printf("syscall(unknown) returned %d (%s)\n", ret, strerror(errno));
+		}
+	}
+
 	exit(error_count);
 }