tests: Emulate multithreading environment for unit tests

The main purpose of this patch is to run unit tests on BSD family
of OSes. The root cause is `fileno` syscall which is a macro that
can be expanded to either a function call (for multi-threaded
environment) or to inline code (for single-threaded environment).
Said inline code accesses private field of file descriptor, and
this construction is impossible to mock in unit tests. Multi-
threaded environment has `fileno` as a function, which can be
mocked in unit tests.

On other OSes the patch just creates a thread which is doing nothing.
We avoid adding pre-processor conditionals since the cost is small.

Tested on
FreeBSD 13.1-RELEASE-p6 GENERIC amd64
NetBSD 9.2 (GENERIC) amd64
OpenBSD 7.2 GENERIC#7 amd64
DragonFly v6.4.0-RELEASE x86_64
Ubuntu 22.04.1 x86_64

Change-Id: I3d65c125183e60037ad07b9d54b8fffdece5a4e8
Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/74157
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Peter Marheine <pmarheine@chromium.org>
Reviewed-by: Thomas Heijligen <src@posteo.de>
---
M tests/meson.build
M tests/tests.c
2 files changed, 54 insertions(+), 12 deletions(-)

diff --git a/tests/meson.build b/tests/meson.build
index df866d7..94f60e2 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -113,6 +113,8 @@
   '-Wl,--gc-sections',
 ]
 
+threads_dep = dependency('threads')
+
 flashrom_tests = executable('flashrom_unit_tests',
   test_srcs,
   c_args : [
@@ -123,7 +125,7 @@
   ],
   export_dynamic : true,
   link_args : mocks + link_args,
-  dependencies : [cmocka_dep, flashrom_test_dep],
+  dependencies : [cmocka_dep, flashrom_test_dep, threads_dep],
 )
 test('cmocka test flashrom', flashrom_tests)
 
diff --git a/tests/tests.c b/tests/tests.c
index 159b79f..8b4ad03 100644
--- a/tests/tests.c
+++ b/tests/tests.c
@@ -22,6 +22,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdint.h>
+#include <pthread.h>
 
 void *not_null(void)
 {
@@ -385,26 +386,32 @@
 	return 0;
 }
 
+static void *doing_nothing(void *vargp) {
+	return NULL;
+}
+
 int main(int argc, char *argv[])
 {
 	int ret = 0;
 
-#if defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
-	/*
-	 * Pretending to be a multithreaded environment so that `fileno`
-	 * is called as a function (and not as a macro).
-	 * fileno macro in FreeBSD is expanded into inline access of
-	 * private field of file descriptor, which is impossible to mock.
-	 * Calling fileno as a function allows the test to mock it.
-	 */
-	__isthreaded = 1;
-#endif
-
 	if (argc > 1)
 		cmocka_set_test_filter(argv[1]);
 
 	cmocka_set_message_output(CM_OUTPUT_STDOUT);
 
+	/*
+	 * Creating new thread which is doing nothing, to trigger __isthreaded being 1.
+	 * This is a workaround for BSD family. In multi-threaded environment fileno
+	 * macro is expanded into a function which is possible to mock in unit tests.
+	 * Without this workaround, on a single-thread environment, fileno macro is
+	 * expanded into an inline access of a private field of a file descriptor,
+	 * which is impossible to mock.
+	 *
+	 * In other OSes this is just creating a thread which is doing nothing.
+	 */
+	pthread_t thread_id;
+	pthread_create(&thread_id, NULL, doing_nothing, NULL);
+
 	const struct CMUnitTest helpers_tests[] = {
 		cmocka_unit_test(address_to_bits_test_success),
 		cmocka_unit_test(bitcount_test_success),

