[FL-3885] Put errno into TCB (#3893)

* feat: thread-safe errno
* ci: fix pvs warning
* ci: silence pvs warning
* fix: 🤯
* test: convert test app into a unit test

applications/debug/unit_tests/tests/furi/furi_errno_test.c

@@ -0,0 +1,51 @@
+#include <furi.h>
+#include <errno.h>
+#include "../test.h" // IWYU pragma: keep
+
+#define TAG        "ErrnoTest"
+#define THREAD_CNT 16
+#define ITER_CNT   1000
+
+static int32_t errno_fuzzer(void* context) {
+    int start_value = (int)context;
+    int32_t fails = 0;
+
+    for(int i = start_value; i < start_value + ITER_CNT; i++) {
+        errno = i;
+        furi_thread_yield();
+        if(errno != i) fails++;
+    }
+
+    for(int i = 0; i < ITER_CNT; i++) {
+        errno = 0;
+        furi_thread_yield();
+        UNUSED(strtol("123456", NULL, 10)); // -V530
+        furi_thread_yield();
+        if(errno != 0) fails++;
+
+        errno = 0;
+        furi_thread_yield();
+        UNUSED(strtol("123456123456123456123456123456123456123456123456", NULL, 10)); // -V530
+        furi_thread_yield();
+        if(errno != ERANGE) fails++;
+    }
+
+    return fails;
+}
+
+void test_errno_saving(void) {
+    FuriThread* threads[THREAD_CNT];
+
+    for(int i = 0; i < THREAD_CNT; i++) {
+        int start_value = i * ITER_CNT;
+        threads[i] = furi_thread_alloc_ex("ErrnoFuzzer", 1024, errno_fuzzer, (void*)start_value);
+        furi_thread_set_priority(threads[i], FuriThreadPriorityNormal);
+        furi_thread_start(threads[i]);
+    }
+
+    for(int i = 0; i < THREAD_CNT; i++) {
+        furi_thread_join(threads[i]);
+        mu_assert_int_eq(0, furi_thread_get_return_code(threads[i]));
+        furi_thread_free(threads[i]);
+    }
+}

applications/debug/unit_tests/tests/furi/furi_test.c

@@ -8,6 +8,7 @@ void test_furi_concurrent_access(void);
 void test_furi_pubsub(void);
 void test_furi_memmgr(void);
 void test_furi_event_loop(void);
+void test_errno_saving(void);
 
 static int foo = 0;
 
@@ -42,6 +43,10 @@ MU_TEST(mu_test_furi_event_loop) {
     test_furi_event_loop();
 }
 
+MU_TEST(mu_test_errno_saving) {
+    test_errno_saving();
+}
+
 MU_TEST_SUITE(test_suite) {
     MU_SUITE_CONFIGURE(&test_setup, &test_teardown);
     MU_RUN_TEST(test_check);
@@ -51,6 +56,7 @@ MU_TEST_SUITE(test_suite) {
     MU_RUN_TEST(mu_test_furi_pubsub);
     MU_RUN_TEST(mu_test_furi_memmgr);
     MU_RUN_TEST(mu_test_furi_event_loop);
+    MU_RUN_TEST(mu_test_errno_saving);
 }
 
 int run_minunit_test_furi(void) {

targets/f7/inc/FreeRTOSConfig.h

@@ -2,6 +2,7 @@
 
 #if defined(__ICCARM__) || defined(__CC_ARM) || defined(__GNUC__)
 #include <stdint.h>
+#include <errno.h>
 #pragma GCC diagnostic ignored "-Wredundant-decls"
 #endif
 
@@ -26,6 +27,7 @@
 #define configUSE_16_BIT_TICKS           0
 #define configMAX_PRIORITIES             (32)
 #define configMINIMAL_STACK_SIZE         ((uint16_t)128)
+#define configUSE_POSIX_ERRNO            1
 
 /* Heap size determined automatically by linker */
 // #define configTOTAL_HEAP_SIZE                    ((size_t)0)
@@ -146,9 +148,14 @@ standard names. */
 #define configOVERRIDE_DEFAULT_TICK_CONFIGURATION \
     1 /* required only for Keil but does not hurt otherwise */
 
-#define traceTASK_SWITCHED_IN()                                     \
-    extern void furi_hal_mpu_set_stack_protection(uint32_t* stack); \
-    furi_hal_mpu_set_stack_protection((uint32_t*)pxCurrentTCB->pxStack)
+#define traceTASK_SWITCHED_IN()                                          \
+    extern void furi_hal_mpu_set_stack_protection(uint32_t* stack);      \
+    furi_hal_mpu_set_stack_protection((uint32_t*)pxCurrentTCB->pxStack); \
+    errno = pxCurrentTCB->iTaskErrno
+//  ^^^^^   acquire errno directly from TCB because FreeRTOS assigns its `FreeRTOS_errno' _after_ our hook is called
+
+// referencing `FreeRTOS_errno' here   vvvvv    because FreeRTOS calls our hook _before_ copying the value into the TCB, hence a manual write to the TCB would get overwritten
+#define traceTASK_SWITCHED_OUT() FreeRTOS_errno = errno
 
 #define portCLEAN_UP_TCB(pxTCB)                                   \
     extern void furi_thread_cleanup_tcb_event(TaskHandle_t task); \