arm: fix initial stack pointer

arm/bootloader.ld

@@ -29,4 +29,6 @@ SECTIONS
         *(.exidx*)
         __exidx_end = .;
     } > ICTM
+
+    _initial_stack_pointer = 16384;
 }

arm/vector_table.cc

@@ -1,6 +1,6 @@
 #include <cstdint>
 
-extern "C" uint32_t _bss_begin, _bss_end;
+extern "C" uint32_t _bss_begin, _bss_end, _initial_stack_pointer;
 extern "C" int main();
 
 namespace {
@@ -25,6 +25,6 @@ void ResetHandler() {
 
 __attribute__((section(".vector_table")))
 uint32_t vector_table[16] = {
-    [StackPointer] = 0x00010000,
+    [StackPointer] = reinterpret_cast<uint32_t>(&_initial_stack_pointer),
     [Reset] = reinterpret_cast<uint32_t>(ResetHandler),
 };