libc: minimal: Fix gmtime() userspace support

The gmtime() function returns a global result variable, and this variable must be placed in the `z_libc_partition` when userspace is enabled. Since gmtime() makes use of a global variable and this results in a footprint increase, this commit makes the time functions optional by introducing `CONFIG_MINIMAL_LIBC_TIME` Kconfig and making them only available when this option is enabled. Signed-off-by: Stephanos Ioannidis <[email protected]>
olofj · Jun 1, 2022 · eb71003 · eb71003
1 parent 2bcb713
commit eb71003
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Showing 3 changed files with 21 additions and 5 deletions.
diff --git a/lib/libc/Kconfig b/lib/libc/Kconfig
@@ -182,6 +182,18 @@ config MINIMAL_LIBC_RAND
 	  In order to make use of the non-reentrant rand() and srand(), it is
 	  necessary to set CONFIG_MINIMAL_LIBC_NON_REENTRANT_FUNCTIONS=y.
 
+config MINIMAL_LIBC_TIME
+	bool "Time functions"
+	default y
+	help
+	  Enable time() and gmtime_r() for the minimal libc.
+
+	  time() requires CONFIG_POSIX_CLOCK=y because it relies on the POSIX
+	  clock_gettime() function.
+
+	  In order to make use of the non-reentrant gmtime(), it is necessary
+	  to set CONFIG_MINIMAL_LIBC_NON_REENTRANT_FUNCTIONS=y.
+
 endif # MINIMAL_LIBC
 
 config STDOUT_CONSOLE

diff --git a/lib/libc/minimal/CMakeLists.txt b/lib/libc/minimal/CMakeLists.txt
@@ -21,10 +21,13 @@ zephyr_library_sources(
   source/stdout/stdout_console.c
   source/stdout/sprintf.c
   source/stdout/fprintf.c
-  source/time/gmtime.c
   source/math/sqrtf.c
   source/math/sqrt.c
 )
 
-zephyr_library_sources_ifdef(CONFIG_POSIX_CLOCK source/time/time.c)
+if(CONFIG_MINIMAL_LIBC_TIME)
+  zephyr_library_sources(source/time/gmtime.c)
+  zephyr_library_sources_ifdef(CONFIG_POSIX_CLOCK source/time/time.c)
+endif()
+
 zephyr_library_sources_ifdef(CONFIG_MINIMAL_LIBC_RAND source/stdlib/rand.c)
diff --git a/lib/libc/minimal/source/time/gmtime.c b/lib/libc/minimal/source/time/gmtime.c
@@ -11,6 +11,7 @@
  */
 
 #include <time.h>
+#include <zephyr/sys/libc-hooks.h>
 
 /* A signed type with the representation of time_t without its
  * implications.
@@ -97,10 +98,10 @@ struct tm *gmtime_r(const time_t *ZRESTRICT timep,
 }
 
 #ifdef CONFIG_MINIMAL_LIBC_NON_REENTRANT_FUNCTIONS
+static Z_LIBC_DATA struct tm gmtime_result;
+
 struct tm *gmtime(const time_t *timep)
 {
-	static struct tm shared;
-
-	return gmtime_r(timep, &shared);
+	return gmtime_r(timep, &gmtime_result);
 }
 #endif /* CONFIG_MINIMAL_LIBC_NON_REENTRANT_FUNCTIONS */