platform: Update picolibc.c for linker script compatibility

Always use picolibc_startup to initialize all .data and .bss
segments. Set the picolibc initialization values for these segments to
all zeros so that the crt0.o code doesn't do anything.

Provide a stub for _set_tls as tf-m doesn't use thread local variables.

Signed-off-by: Keith Packard <[email protected]>

Author: keith-packard

platform/ext/common/picolibc.c

@@ -9,15 +9,15 @@
 #include <string.h>
 #include "config_impl.h"
 
+#ifdef __PICOLIBC__
+
 /*
  * Picolibc's startup code only initializes a single data and bss
  * segment.  Augment that by initializing the remaining segments using
  * the lists provided by the linker script in a constructor which will
  * be called from _start
  */
 
-#if defined(__PICOLIBC__) && TFM_ISOLATION_LEVEL > 0
-
 static void __attribute__((constructor))
 picolibc_startup(void)
 {
@@ -45,4 +45,44 @@ picolibc_startup(void)
     memset(pTable->dest, 0, pTable->wlen << 2);
   }
 }
+
+/*
+ * Create symbols for picolibc. These are used by the
+ * startup code to initialize memory, but that work
+ * is done by the function above
+ */
+
+__asm__(".globl __data_source\n"
+        ".globl __data_start\n"
+        ".globl __data_size\n"
+        ".globl __bss_size\n"
+        ".globl __bss_start\n"
+        ".equ __data_source, 0\n"
+        ".equ __data_start, 0\n"
+        ".equ __data_size, 0\n"
+        ".equ __bss_size, 0\n"
+        ".equ __bss_start, 0");
+
+#ifdef __THREAD_LOCAL_STORAGE
+
+__asm__(".globl __tls_base\n"
+        ".equ __tls_base, 0");
+
+#include <picotls.h>
+
+/*
+ * Picolibc's startup code wants to initialize the thread local
+ * storage base address, but tf-m doesn't use any TLS variables.
+ *
+ * Stub out this function until TLS is required.
+ */
+
+void
+_set_tls(void *tls_base)
+{
+    (void) tls_base;
+}
+
 #endif
+
+#endif /* __PICOLIBC__ */