dbg: map addresses to file+function+offset

Add support for mapping kernel .text addresses into file + function +
offset for debugging purposes. Make the backtrace use this new feature.

kernel-src/lib/dbg.c

@@ -0,0 +1,45 @@
+#include <dbg.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __x86_64__
+#define LOAD_BASE (uint64_t)0xffffffff80000000
+#endif
+
+#define SYM_TABLE_ENTRY_SIZE 3
+extern uint32_t dbg_sym_table[];
+extern uint32_t dbg_sym_table_end[];
+
+extern char dbg_fn_name_table[];
+extern char dbg_fn_name_table_end[];
+
+extern char dbg_file_name_table[];
+extern char dbg_file_name_table_end[];
+
+void dbg_get_symbol(void *rip, char **fn_name, char **file_name, size_t *offset) {
+	*fn_name = "??";
+	*file_name = "??";
+	*offset = 0;
+
+	if ((uint64_t)rip < LOAD_BASE)
+		return;
+
+	uint64_t rip_offset = (uint64_t)rip - LOAD_BASE;
+	size_t low = 0;
+	size_t high = (dbg_sym_table_end - dbg_sym_table) / SYM_TABLE_ENTRY_SIZE;
+	while (low < high) {
+		size_t mid = low + (high - low) / 2;
+		if (dbg_sym_table[mid * SYM_TABLE_ENTRY_SIZE] <= rip_offset)
+			low = mid + 1;
+		else
+			high = mid;
+	}
+
+	if (low == 0)
+		return;
+
+	uint32_t *symbol = dbg_sym_table + (low - 1) * SYM_TABLE_ENTRY_SIZE;
+	*fn_name = dbg_fn_name_table + symbol[1];
+	*file_name = dbg_file_name_table + symbol[2];
+	*offset = rip_offset - symbol[0];
+}

kernel-src/lib/panic.c

@@ -4,11 +4,17 @@
 #include <printf.h>
 #include <kernel/interrupt.h>
 #include <arch/backtrace.h>
+#include <dbg.h>
 
 static bool paniced = false;
 
 static bool step_backtrace(void *, void *ip) {
-	printf("%p\n", ip);
+	char *fn, *file;
+	size_t off;
+
+	dbg_get_symbol(ip, &fn, &file, &off);
+
+	printf("%p: %s:%s+%x\n", ip, file, fn, off);
 	return true;
 }