Gcov: Enable Code coverage reporting over UART.

This patch provides support for generating Code coverage reports.
The prj.conf needs to enable CONFIG_COVERAGE. Once enabled, the
code coverage data dump now comes via UART.
This data dump on the UART is triggered once the main
thread exits.

Next step is to save this data dump on file. Then run
scripts/gen_gcov_files.py with the serial console log as argument.

The last step would be be to run the gcovr. Use the following cmd
 gcovr -r . --html -o gcov_report/coverage.html --html-details

Currently supported architectures are ARM and x86.

Signed-off-by: Adithya Baglody <[email protected]>

arch/Kconfig

@@ -162,6 +162,7 @@ config PRIVILEGED_STACK_TEXT_AREA
 
 config KOBJECT_TEXT_AREA
 	int "Size if kobject text area"
+	default 512 if COVERAGE_GCOV
 	default 256 if (!SIZE_OPTIMIZATIONS || STACK_CANARIES || ARC)
 	default 256 if CODE_DATA_RELOCATION
 	default 128

include/linker/common-rom.ld

@@ -41,6 +41,18 @@
 		__object_access_end = .;
 	}
 #endif
+
+#ifdef CONFIG_COVERAGE_GCOV
+	/* Section needed by gcov when coverage is turned on.*/
+	SECTION_PROLOGUE (gcov, (OPTIONAL),)
+	{
+		PROVIDE_HIDDEN (__init_array_start = .);
+		KEEP (*(SORT(.init_array.*)))
+		KEEP (*(.init_array*))
+		PROVIDE_HIDDEN (__init_array_end = .);
+	} GROUP_LINK_IN(ROMABLE_REGION)
+#endif  /* CONFIG_COVERAGE_GCOV */
+
 	SECTION_PROLOGUE (devconfig, (OPTIONAL),)
 	{
 		__devconfig_start = .;

kernel/init.c

@@ -33,6 +33,7 @@
 #include <logging/log_ctrl.h>
 #include <tracing.h>
 #include <stdbool.h>
+#include <misc/gcov.h>
 
 #define IDLE_THREAD_NAME	"idle"
 #define LOG_LEVEL CONFIG_KERNEL_LOG_LEVEL
@@ -156,6 +157,10 @@ void _bss_zero(void)
 	(void)memset(&__app_bss_start, 0,
 		     ((u32_t) &__app_bss_end - (u32_t) &__app_bss_start));
 #endif
+#ifdef CONFIG_COVERAGE_GCOV
+	(void)memset(&__gcov_bss_start, 0,
+		 ((u32_t) &__gcov_bss_end - (u32_t) &__gcov_bss_start));
+#endif
 }
 
 
@@ -252,6 +257,9 @@ static void bg_thread_main(void *unused1, void *unused2, void *unused3)
 
 	main();
 
+	/* Dump coverage data once the main() has exited. */
+	gcov_coverage_dump();
+
 	/* Terminate thread normally since it has no more work to do */
 	_main_thread->base.user_options &= ~K_ESSENTIAL;
 }
@@ -453,6 +461,9 @@ extern uintptr_t __stack_chk_guard;
  */
 FUNC_NORETURN void _Cstart(void)
 {
+	/* gcov hook needed to get the coverage report.*/
+	gcov_static_init();
+
 #ifdef CONFIG_MULTITHREADING
 #ifdef CONFIG_ARCH_HAS_CUSTOM_SWAP_TO_MAIN
 	struct k_thread *dummy_thread = NULL;