libspl/assert: show process/task details in assert output

Makes it much easier to see what thing complained.

Getting thread id, program name and thread name vary wildly between
Linux and FreeBSD, so those are set up in macros. pthread_getname_np()
did not appear in musl until very recently, but the same info has always
been available via prctl(PR_GET_NAME), so we use that instead.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Rob Norris <[email protected]>
Sponsored-by: https://despairlabs.com/sponsor/
Closes openzfs#16140

Author: robn

config/user.m4

@@ -31,7 +31,7 @@ AC_DEFUN([ZFS_AC_CONFIG_USER], [
 	ZFS_AC_CONFIG_USER_MAKEDEV_IN_MKDEV
 	ZFS_AC_CONFIG_USER_ZFSEXEC
 
-	AC_CHECK_FUNCS([execvpe issetugid mlockall strlcat strlcpy])
+	AC_CHECK_FUNCS([execvpe issetugid mlockall strlcat strlcpy gettid])
 
 	AC_SUBST(RM)
 ])

lib/libspl/assert.c

@@ -22,9 +22,32 @@
  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
+/*
+ * Copyright (c) 2024, Rob Norris <[email protected]>
+ */
 
 #include <assert.h>
 
+#if defined(__linux__)
+#include <errno.h>
+#include <sys/prctl.h>
+#ifdef HAVE_GETTID
+#define	libspl_gettid()		gettid()
+#else
+#include <sys/syscall.h>
+#define	libspl_gettid()		((pid_t)syscall(__NR_gettid))
+#endif
+#define	libspl_getprogname()	(program_invocation_short_name)
+#define	libspl_getthreadname(buf, len)	\
+	prctl(PR_GET_NAME, (unsigned long)(buf), 0, 0, 0)
+#elif defined(__FreeBSD__)
+#include <pthread_np.h>
+#define	libspl_gettid()		pthread_getthreadid_np()
+#define	libspl_getprogname()	getprogname()
+#define	libspl_getthreadname(buf, len)	\
+	pthread_getname_np(pthread_self(), buf, len);
+#endif
+
 static boolean_t libspl_assert_ok = B_FALSE;
 
 void
@@ -39,13 +62,22 @@ libspl_assertf(const char *file, const char *func, int line,
     const char *format, ...)
 {
 	va_list args;
+	char tname[64];
+
+	libspl_getthreadname(tname, sizeof (tname));
+
+	fprintf(stderr, "ASSERT at %s:%d:%s()\n", file, line, func);
 
 	va_start(args, format);
 	vfprintf(stderr, format, args);
-	fprintf(stderr, "\n");
-	fprintf(stderr, "ASSERT at %s:%d:%s()", file, line, func);
 	va_end(args);
 
+	fprintf(stderr, "\n"
+	    "  PID: %-8u  COMM: %s\n"
+	    "  TID: %-8u  NAME: %s\n",
+	    getpid(), libspl_getprogname(),
+	    libspl_gettid(), tname);
+
 #if !__has_feature(attribute_analyzer_noreturn) && !defined(__COVERITY__)
 	if (libspl_assert_ok) {
 		return;