initial commit

port/moonlight/bootup.c

@@ -0,0 +1,101 @@
+/*
+   Simple C++ startup routine to setup CRT
+   SPDX-License-Identifier: Unlicense
+
+   (https://five-embeddev.com/ | http://www.shincbm.com/) 
+
+*/
+
+#include <stdint.h>
+#include <string.h>
+
+#ifdef __cplusplus
+#define EXTERN_C extern "C"
+#else
+#define EXTERN_C extern
+#endif 
+
+// Generic C function pointer.
+typedef void(*function_t)(void) ;
+// These symbols are defined by the linker script.
+// See linker.lds
+EXTERN_C uint8_t __bss_start;
+EXTERN_C uint8_t __bss_end;
+EXTERN_C const uint8_t __data_source;
+EXTERN_C uint8_t __data_start;
+EXTERN_C uint8_t __data_end;
+
+EXTERN_C function_t __init_array_start;
+EXTERN_C function_t __init_array_end;
+EXTERN_C function_t __fini_array_start;
+EXTERN_C function_t __fini_array_end;
+
+// This function will be placed by the linker script according to the section
+// Raw function 'called' by the CPU with no runtime.
+EXTERN_C void _start(void)  __attribute__ ((naked,section(".text.init")));
+
+// Entry and exit points as C functions.
+EXTERN_C void _initialize(void) __attribute__ ((noreturn,section(".init")));
+EXTERN_C void _exit(int exit_code) __attribute__ ((noreturn,noinline,weak));
+
+// Standard entry point, no arguments.
+extern int main(void);
+
+// The linker script will place this in the reset entry point.
+// It will be 'called' with no stack or C runtime configuration.
+// NOTE - this only supports a single hart.
+// tp will not be initialized
+void _start(void) {
+    // Setup SP and GP
+    // The locations are defined in the linker script
+    __asm__ volatile  (
+        ".option push;"
+        // The 'norelax' option is critical here.
+        // Without 'norelax' the global pointer will
+        // be loaded relative to the global pointer!
+         ".option norelax;"
+        "la    gp, __global_pointer$;"
+        ".option pop;"
+        "la    sp, _sp;"
+        "jal   zero, _initialize;"
+        : /* output: none %0 */
+        : /* input: none */
+        : /* clobbers: none */); 
+    // This point will not be executed, _initialize() will be called with no return.
+}
+
+// At this point we have a stack and global poiner, but no access to global variables.
+void _initialize(void) {
+    // Init memory regions
+    // Clear the .bss section (global variables with no initial values)
+    memset((void*) &__bss_start,
+           0, 
+           (&__bss_end - &__bss_start));
+    // Initialize the .data section (global variables with initial values)
+    memcpy((void*)&__data_start,
+           (const void*)&__data_source,
+           (&__data_end - &__data_end));
+    // Call constructors
+    for (const function_t* entry=&__init_array_start; 
+         entry < &__init_array_end;
+         ++entry) {
+        (*entry)();
+    }
+    int rc = main();
+    // Call destructors
+    for (const function_t* entry=&__fini_array_start; 
+         entry < &__fini_array_end;
+         ++entry) {
+        (*entry)();
+    }
+    _exit(rc);
+}
+
+// This should never be called. Busy loop with the CPU in idle state.
+void _exit(int exit_code) {
+    (void)exit_code;
+    // Halt
+    while (1) {
+        __asm__ volatile ("wfi");
+    }
+}